New technologies or innovative treatment lines for reliable water treatment for P&P and minimization of waste production ppt

Challenges for water re-use in the Pulp&Paper industry are the following: process and the paper quality; - The removal of sticky solids and suspended solids, which can induce plugging of

food industries

New technologies or innovative treatment lines for reliable water treatment for P&P and minimization of

waste production

B Simstich, J Rumpel, H Jung, P Hiermeier, G Weinberger,

D Pauly, S Bierbaum, H.-J Öller, C Hentschke (PTS)

M Engelhart, J.v Düffel, M Wozniak (ENV)

D Hermosilla, N Merayo, R Ordoñez, L Blanco, H Barndok, L Cortijo, P López, J Tijero, C Negro, A Blanco (UCM)

A Rodriguez (HOL)

M Bromen, J Vogt, J Mielcke, (WED)

January 2012

Executive summary

This report is a result of the project AquaFit4Use, a large-scale European research project financed by the 7th framework program of the European Union on water treatment technologies and processes

co-In the Pulp&Paper industry a lot of effort is put into to water saving and closing water circuits, also reducing substantially the environmental impact, both by process modelling and Kidney technologies as internal process water treatment However a number of problems around the removal of substances are not solved yet and further closing of the water cycle causes other problems Challenges for water re-use in the Pulp&Paper industry are the following:

process and the paper quality;

- The removal of sticky solids and suspended solids, which can induce plugging of pipes and showers, deposit formation, abrasion, loss of tensile strength;

- The treatment of concentrate streams containing calcium, sulphate, chloride and organics which can lead to salt accumulation in case of water loop closure, corrosion, scaling of pipes and showers in the paper production process The removal of calcium carbonate is crucial in the last case

Therefore there is a need to find new and reliable (combinations of) technologies to solve this challenges to achieve the water quality target for water re-use and which are tailored to suit product demands and standards

The work described in this report concerned the laboratory and preliminary work for the implementation of pilot trials on two industrial paper mills The emphasis was on different technologies as part of a global treatment line to solve the above challenges

On the basis of waste water characterization and the defined water quality requirements for paper mills, new treatment lines were defined to reach the water quality target including effectiveness, reliability and minimization in waste and concentrate production These new treatment lines are focused on internal recycling

The emphasis was on different key steps of the global treatment train:

- Biological treatment: anaerobic processes and MBR;

- Filtration processes: 3FM high speed technology and nanofiltration;

- Tertiary treatments to reduce hard COD: AOPs, coagulation/precipitation;

- Integration of processes (evapoconcentration, electrodialysis and softening) in the treatment line:

o To treat the concentrate streams containing calcium, sulphate, chloride, organics;

o To minimize the waste production and enhance internal recycling

Technologies were tested at lab scale on the waste waters from 3 different paper mills:

• Paper mill 1 (PM1), producing corrugated board and board;

• Paper mill 2 (PM2), producing high quality coated and uncoated board from recycled paper;

• Paper mill 3 (PM3), producing standard newsprint, improved newsprint (higher brightness) and light weight coated paper (for magazines)

On basis of the obtained results, the best treatment combinations to be implemented and tested

at pilot scale within WP5.1.4 were selected as summarized below for each type of paper mill:

a) Corrugated board paper mills (PM1 and PM2)

Most important findings are:

• Stable MBR operation is not possible at calcium concentrations > 400 mg/l due to scaling problems Softening upstream of the MBR is than absolutely necessary Trials with a lime softening stage showed a removal of 50 – 80 % of the Ca2+ concentration in the feed (600 – 1000 mg/l)

• Ozone trials with pre-filtered final effluent of both mills led to a COD reduction by about 20- 25% Economical viable specific ozone dosages of 0.25 to 0.7 g O3/g COD0 have been used Overall it is more costly and complex to achieve COD levels below ~50 mg/l The increased BOD5 shows that a subsequent biological treatment can be promising for further COD reduction The water can be reused in the production process, especially because the water after ozone treatment is visibly colour-free Possible reuse processes are showers at the paper machine were it can be used instead of fresh water Calcium concentrations may be a limiting factor for reuse

• NF membranes with high retention capacity for monovalent ions (Dow Filmtec NF 90 and Koch TFC ULP) are able to fulfil quality requirements for white grade paper reclamation water (for PM1 and PM2)

• Intensive pre-treatment or conditioning is needed to obtain steady NF membrane performance and high recovery rates due to the high scaling tendency (membrane blocking) of aerobic effluents of both PMs Reduction of pH to around pH 6.5 (HCl) and dosing of anti-scalant was necessary to achieve recovery rates of 80% Softening of wastewater allowed higher recovery up to 93% and lower chemical consumption for conditioning (no-use of hydrochloric acid)

In this view, the MultifloTM softening technology (lime softening) is well adapted to remove calcium carbonate

Long term stability of membrane treatment (plateau formation, high system recovery) needs to be evaluated on pilot scale continuously

• 3FM technology showed good performances at lab scale regarding TSS removal and turbidity reduction These have to be confirmed at pilot scale

Most important findings concerning the treatment of concentrates of PM1 and PM2 are:

• Evapoconcentration proved to be an adapted technology to treat NF concentrates in terms

of production of a colourless water with a quality fulfilling the water quality criteria of both paper mills for re-use and to reduce the final volume of concentrates:

o Reduction of wastes as a global volumic concentration factor VCF up to 50 for combined “NF+evapoconcentration” could be obtained at lab scale for PM2 and 25 for PM1

These global VCFs should be increased at industrial scale to 60 without NF membrane pre-treatment and up to 250 with 3FM/softening as pre-treatment provided conversion rate on NF process and pre-treatment processes are the same at pilot scale Then the addition of evapoconcentration would lead to a final concentrate to be disposed off representing respectively 1.7% to 0.4% in the last case in volume of the waste water treated by the global treatment line

o Pre-treatments before NF process have a positive impact on the global VCF which could be reached at industrial scale leading to a very substantial reduction of the volume of final waste to be disposed off down to 0.4% in the case of 3FM combined with softening as pre-treatment

• AOP treatment: High conductivity and chloride concentrations > 4,000 mg/l prevented biological degradation after AOP treatment To reduce chloride intake to the wastewater, softening before membrane processes is preferable to acidification with HCl

• Re-injection of NF concentrates has a negative impact on anaerobic degradation rate in pellet sludge reactors

Based on these results, following treatment trains have been selected to be tested on site at pilot scale within WP5.1.4:

Impact of reinjection???

Water to be re-used ?

Final waste

Water to be re-used ?

Water to be re-used ?

Water to be re-used ?

Can be recycled into Anaerobic ???

Final waste Water to be

re-used ? NF

AOP (O 3 )

AOP (O 3 )

Evapo 3FM

Multiflo softening

Water to be re-used ?

Impact of reinjection???

Water to be re-used ?

Final waste

Water to be re-used ?

Water to be re-used ?

NF

softening Multiflo softening

AOP (O 3 ) AOP (O 3 )

AOP (O 3 ) AOP (O 3 )

Evapo MBR

Water to be re-used ?

Can be recycled into Anaerobic ???

Final waste Water to be

re-used ? NF

AOP (O 3 )

AOP (O 3 ) AOP (O 3 )

Evapo 3FM

Multiflo softening Multiflo softening

Water to be re-used ?

b) Newsprint paper mill (PM3)

Most important findings derived from PM3 effluent treatment are:

• Although AOP treatments are efficient for bio-recalcitrant organics removal, due to the high amount of volatile fatty acids that are difficult to oxidize and consume high amounts of OH·, in the effluent of PM3 a previous biological treatment is expected to be more reliable Despite this, colour removal was higher than 95% and COD removals vary between 20 to 40% In addition, AOPs processes improve biodegradability of the treated effluent

• Anaerobic pre-treatment showed very good performance treating a low organic load wastewater as the effluent of a 100% recycled NP/LWC paper mill, and assisting the aerobic stage on removing organics and sulphates; besides it produced enough biogas for being considered as cost-effective

• The biological treatments studied in the two pilot plants achieved a final COD, BOD5 and sulphates removal of 80-85%, 95-99% and 25-35%, respectively Wastewater quality after biological treatment resulted suitable to further perform a posterior membrane treatment

• Membrane treatment by UF + RO is able to generate permeates of high water quality, fulfilling all the requirements for being used in critical points of the paper machine that require a very high water quality

• 3FM filtration followed by acidification seemed to have a positive effect on membrane treatment A higher recovery rate was obtained and permeate with a very good quality was obtained These results would have to be confirmed at pilot scale as the RO process was performed on a membrane test cell

Most important findings derived from the application of evapoconcentration, coagulation / softening / flocculation treatment and AOPs to the treatment of RO concentrates from PM3 are:

• Evapoconcentration proved to be an adapted technology to treat membrane concentrates

of both tested treatment trains (Anaerobic
Aerobic
3FM
RO and Anaerobic
MBR
RO) In both cases the produced water (final VCF = 11.5-11.7) has a very good quality respecting all PM3 requirements for re-use as fresh water

Considering the VCF of the RO step, the addition of evapoconcentration would then lead

to a final waste to be disposed off representing respectively 2.8% and 7% in volume of the waste water treated by the global treatment line

• Coagulation eliminated more than 95% of coloured compounds with a high level of resonance (A500), however, high coagulant doses were needed, making the process economically unfeasible Besides, PACl addition by itself increases conductivity

• Lime-softening was a good alternative to reduce conductivity Organic matter was adsorbed on Mg(OH)2 and CaCO3 surface and, thus, additionally removed in the precipitation process

• Coagulating water with 2500 mg/L of PACl1 in the presence of lime and a PAM produces a 60% COD removal, independently of the pH and the dosage

• Fenton and photo-Fenton processes were optimised by response surface methodology Low pH and high [H2O2] were optimum conditions for both methods Low ferrous ion concentration might achieve good COD removals with photo-Fenton process and Fenton process need higher ferrous ion concentrations More than 50% of COD removal may be obtained at neutral pH

• AOPs led to a high removal of COD at laboratory scale Photo-Fenton obtained the best COD removal (99%) followed by Fenton (90%) processes in comparison to the 40% achieved by ozone processes

• Photocatalysis at laboratory scale did not obtain so high COD and TOC removals from RO reject, but the combination of photocatalysis treatment (10 g/L of TiO2) with biological treatments got a total removal of COD from the wastewater

Based on these results, following treatment trains have been selected to be tested on site at pilot scale within WP5.1.4 in PM3:

Pilot plant 2

Important note: This final deliverable is a compilation of all lab scale results performed within WP3.1, which have been reported in details in following internal results:

• I3.1.1.1 Proof of concept of aerobic water treatment technologies and separation

techniques on bench scale for Pulp & Paper

• I3.1.1.2 Proof of concept of anaerobic water treatment technologies and MBR techniques

on bench scale for Pulp & Paper

• I3.1.1.3 Assessment of technologies for the treatment of membrane retentate streams for

Pulp & Paper

• I3.1.1.4 Assessment of technologies for the elimination of inorganic compounds for Pulp &

Paper

Content

EXECUTIVE SUMMARY 2

CONTENT 7

1 INTRODUCTION 9

1.1 STATE OF THE ART 9

1.1.1 Waste water treatment in Paper industry (Jung and Pauly, 2011) 9

1.1.2 State-of-the-art of tested technologies within the study 14

1.2 OBJECTIVES 35

2 METHODS 36

2.1 METHODS 36

2.1.1 Paper mill 1 (PM1) 37

2.1.2 Paper mill 2 (PM2) 39

2.1.3 Paper mill 3 (PM3) 41

2.2 MATERIALS AND EQUIPMENT 43

2.2.1 MBR processes 43

2.2.2 3FM technology 44

2.2.3 Membrane technologies (UF, NF, RO) 46

2.2.4 AOP technologies 47

2.2.5 Evapoconcentration 50

2.2.6 Electrodialysis 51

2.2.7 Softening and controlled precipitation technologies 52

2.2.8 Biodegradability experiments (PM1, PM2 and PM3) 52

3 RESULTS AND ACHIEVEMENTS 55

3.1 MAJOR RESULTS AND ACHIEVEMENTS 55

3.1.1 Corrugated paper mill (PM1 and PM2) 55

3.1.2 News print paper mill (PM3) 58

3.2 TECHNICAL PROGRESS OF THE WORK 60

3.2.1 Corrugated paper mill (PM1 and PM2) 60

3.2.2 Newsprint paper mill (PM3) 86

4 CONCLUSIONS 116

4.1 MAJOR ACHIEVEMENTS 116

4.1.1 Corrugated board paper mills (PM1 and PM2) 116

4.1.2 Newsprint paper mill (PM3) 117

4.2 FUTURE WORK 119

4.2.1 Within AquaFit4Use 119

4.2.2 General recommendations 120

5 LITERATURE 121

6 ANNEX 128

6.1 ANNEX ON EVAPOCONCENTRATION 128

6.2 DETAILED RESULTS ON PM1 129

6.3 DETAILED RESULTS ON PM2 130

6.4 DETAILED RESULTS ON PM3 132

6.5 3FM FILTRATION TESTS ON PM1 AND PM2 ANAEROBIC EFFLUENT 133

6.7 SOFTENING TESTS ON PM2 WASTE WATER 137

6.7.1 Softening on Aerobic effluent 137

6.7.2 Multiflo TM Softening on 3FM filtrate 138

6.8 EVAPOCONCENTRATION APPLIED TO NF CONCENTRATES FROM PM1 AND PM2 139

6.9 ELECTRODIALYSIS ON RO CONCENTRATES FROM PM2 AND PM3 140

6.10 3FM FILTRATION APPLIED TO PM3 ANAEROBIC/AEROBIC EFFLUENT 141

6.11 NF/RO SCREENING ON 3FM FILTRATE FROM PM3(OSMONIC FILTRATION CELL) 142

6.12 EVAPOCONCENTRATION ON RO CONCENTRATES FROM PM3 144

6.12.1 RO concentrates from “PM3 waste water
Anaerobic
Aerobic
3FM
RO” 144

6.12.2 RO concentrates from “PM3 waste water
Anaerobic
MBR
RO” 145

6.13 COAGULATION/SOFTENING/FLOCCULATION OF RO CONCENTRATES FROM PM3 146

1 Introduction

This report is a result of the project AquaFit4Use, a large-scale European research project financed by the 7th framework programme of the European Union on water treatment technologies and processes

co-The research objectives of AquaFit4Use are the development of new, reliable cost-effective technologies, tools and methods for sustainable water supply use and discharge in the main water using industries in Europe in order to reduce fresh water needs, mitigate environmental impact, produce and use water of a quality in accordance with the industries specifications (fit-for-use), leading to a further closure of water cycle

This report corresponds to the Task 3.1.1 “Evaluation of tailor-made water treatment concepts for different water qualities, sustainable water reuse and more reliable technologies connected with Pulp&Paper” of WP3.1 in SP3

For more information on AquaFit4Use, please visit the project website: www.aquafit4use.eu

In the Pulp&Paper industry a lot of effort is used to water saving and closing water circuits, and to reducing substantially the environmental impact, also by process modelling and Kidney technologies as internal process water treatment However a number of problems around the removal of substances are not solved yet and further closing of the water cycle causes other

problems Challenges for water re-use in the Pulp&Paper industry are the following (Negro et al

1995):

process and the paper quality;

- The removal of sticky solids and suspended solids, which can induce plugging of pipes and showers, deposit formation, abrasion, loss of tensile strength;

- The treatment of concentrate streams containing calcium, sulphate chloride organics which can lead to salt accumulation in case of case of water loop closure, corrosion, scaling of pipes and showers in the paper production process The removal of calcium carbonate is crucial in the last case

Therefore there is a need to find new and reliable (combinations of) technologies to solve this challenges to achieve the water quality target for water re-use and which are tailored to suit product demands and standards

The work described in this report concerned the laboratory and preliminary work for the implementation of pilot trials on two industrial paper mills Focus was done on different technologies as part of a global treatment line to solve the above challenges Comparison was done to select the best treatment combinations to be implemented at pilot scale

1.1 State of the art

1.1.1 Waste water treatment in Paper industry (Jung and Pauly, 2011)

1.1.1.1 Preliminary mechanical treatment - Mechanical processes for solids removal

Effluents from pulp and paper mills contain solids and dissolved matter Principal methods used to remove solids from pulp and paper mills effluents are screening, settling/clarification and flotation

The separation of solids from the effluents is accomplished with help of screens, grid chambers and settling tanks Screens are units which operate according to the sieving/filtration process The function of the screens is to remove coarse, bulky and fibrous components from the effluents If necessary, fractionated particle separation can be achieved by graduating the gap width (bar screen, fine screen, inlet screen, ultra-fine screen)

For reasons of operating reliability of waste water treatment plants, it is also necessary to separate the grit transported with the effluents and other mineral materials from the degradable organic material Grit separation from effluents can prevent operational troubles such as grit sedimentation, increased wear and clogging The grit separating systems currently in use are subdivided into longitudinal grit traps, circular grit traps and vortex grit traps, depending on their design and process layout

Sedimentation technology is the simplest and most economical method of separating solid substances from the liquid phase High efficiency is achieved in subsequent effluent treatment processes when the solid substances suspended in the effluents settle in a sedimentation tank as completely as possible, and settled sludge is removed from the sedimentation tank Sedimentation tanks must be appropriately designed and operated Alternative sedimentation equipment with sets of lamella-shaped passages, are employed in the paper industry, especially for effluents with high fibre concentrations

Mechanical effluent treatment alone, however, is not sufficient to keep lakes and rivers clean, since it is incapable of removing colloidal suspended and dissolved substances

1.1.1.2 Biological treatment

Biological waste water treatment is designed to degrade pollutants dissolved in effluents by the action of micro-organisms The micro-organisms utilize these substances to live and reproduce Pollutants are used as nutrients Prerequisite for such degradation activity, however, is that the pollutants are soluble in water and non-toxic Degradation process can take place either in the presence of oxygen (aerobic treatment) or in the absence of oxygen (anaerobic treatment) Both naturally occurring principles of effluent treatment principles give rise to fundamental differences in the technical and economic processes involved (Table 1)

Table 1: Advantages and disadvantages of anaerobic and aerobic waste water treatment

(Chernicharo, 2007)

Anaerobic treatment Aerobic treatment

Low production of excess sludge 3 to 5

Sensitive against high sulphate and

calcium concentrations

No fully biological degradation

Possibility of preservation of the biomass

with no reactor feeding for several

months

Low nutrient consumption

Application in small and large scale

The paper industry uses a variety of effluent treatment systems The preferred process combination for each individual case depends on the grade-specific quality of the effluent that is going to be treated Experience shows that multi-stage processes based on an aerobic-aerobic or anaerobic-aerobic processing principle enables significantly more reliable operation of the plant The same effect can be achieved through a cascade system which allows a graduation of the loading conditions Among the German pulp and paper mills with on-site waste water treatment plants, 60 % have only aerobic treatment (operated as one- or two-stage processes) for their effluents, whereas 40 % have an additional anaerobic stage (Jung et al., 2009)

a) Anaerobic treatment

Anaerobic processes are employed for treatment of more highly polluted effluents such as effluents from recovered paper converting mills (Hamm, 2006) Anaerobic micro-organisms conduct their metabolism only in the absence of oxygen Anaerobic processes are characterized

by a small amount of excess sludge produced and low energy requirements As biogas is produced during the degradation process, anaerobic processes produce an excess of energy Biogas is a mixture of its principal components methane and carbon dioxide with traces of hydrogen sulfide, nitrogen and oxygen Biogas is energetically utilized mainly in internal combustion engines or boilers In its function as a regenerative energy carrier, biogas replaces fossil fuels in generation of process steam, heat and electricity Composition and quality of biogas depends on both effluent properties and process conditions such as temperature, retention time and volume load

Before discharge into surface waters, anaerobically treated effluents have to undergo aerobic post-treatment, because – according to the current state of the art – fully biological degradation of paper mill effluents is not feasible (Möbius, 2002)

When introducing anaerobic technology into the pulp and paper industry, operational problems and their possible consequences shown in Table 2 must be taken into account:

Table 2: Operational problems and possible consequences on anaerobic treatment in the pulp

and paper industry

Operational problem Possible consequences

High concentrations of suspended solids in

Inhibiting or toxic effects of sulfide Performance losses

Additives used in production (especially

biocides and detergents) Inhibiting/toxic influences Poorer degradation performance

Decomposition/wash-out of pellets

Loss of pellets

Performance losses Fluctuating organics loads (e.g shock loads) Excessive production of organic acids

Methanation disturbed

b) Aerobic treatment

Aerobic micro-organisms require oxygen to support their metabolic activity In effluent treatment, oxygen is supplied to the effluent in the form of air by special aeration equipment Bacteria use dissolved oxygen to convert organic components into carbon dioxide and biomass In addition, aerobic micro-organisms convert ammonified organic nitrogen compounds and oxidize ammonium and nitrite to form nitrate (nitrification) The key factors for the success of an aerobic process are an adequate amount of nutrients in relation to the amount of biomass, certain temperature and pH regime and the absence of toxic substances (Hynninen, 2000) Aerobic processes are characterized by high volumes of excess sludge and higher energy demands compared to anaerobic processes Furthermore, these reactors typically have large space requirements

Aerobic treatment allows fully biological degradation of paper mill effluents The BOD5 efficiency achievable with well operated activated sludge processes is typically within the range of 90-98 % (Hamm, 2006) The drawbacks of aerobic treatment technology are the relatively high operating costs due to the aeration of the effluent On the other hand, aerobically operated plants exhibit higher plant stability and are less sensitive to fluctuations in effluent and plant parameters

Among different types of aerobic treatment technologies, activated sludge processes are currently the most frequently used treatment technologies in the German pulp and paper industry and have achieved a share of three quarters of the operating reactors Both Moving Bed Bio Reactors (MBBR) and biofilters represent another 10 % of the reactors used (Jung et al., 2009)

c) Secondary clarification

Secondary clarification is intended to separate the biomass (activated sludge) formed in biological reactors and is therefore a key element in all processes employed in the final stage of a treatment plant The quality of the separation process is just as crucial for the final effluent quality as is biological treatment itself

As far as activated sludge process is concerned, secondary clarification determines the bioreactor performance Separation and thickening of the recirculated sludge is crucial for sludge volumes in biological treatment and also for the potential sludge loading Correct dimensioning of secondary clarification is therefore of maximum importance for overall plant performance

1.1.1.3 Advanced and tertiary treatment

Tertiary and/or advanced waste water treatment is used to remove specific waste water constituents that cannot be removed by secondary treatment Different treatment processes are necessary to remove nitrogen, phosphorus, additional suspended solids, refractory organics or dissolved solids Sometimes it is referred to as tertiary treatment because advanced treatment usually follows high-rate secondary treatment However, advanced treatment processes are sometimes combined with primary or secondary treatment (e.g., chemical addition to primary clarifiers or aeration basins to remove phosphorus) or used in place of secondary treatment (e.g overland flow treatment of primary effluent) Reasons for advanced effluent treatment are:

• Reduction in costs (discharge fee);

• Compliance with limit values;

• Increase in production

Table 3: Treatment aims of different advanced treatment methods

Treatment method Aim of treatment

Removal of suspended solids

Decoloration

Elimination of suspended solids Demineralization

Decoloration

De-nitrification and phosphate precipitation Nitrogen and phosphate elimination

Advanced waste water treatment in the pulp and paper industry is focused mainly on additional biological membrane reactors, ozone treatment and membrane filtration techniques such as micro-, ultra- or nanofiltration and reverse osmosis Due to relatively little full-scale experience, relatively high costs and greater complexity of water treatment, there have been only few full-scale applications of tertiary treatment of mill effluents up to now

The method that is ultimately chosen depends on the treatment aim and economic efficiency of the method in a given application

1.1.1.4 Water circuits and quality demands in paper production

In the history of papermaking, the water circuit was created as a result of the invention of the paper machine and with it the advent of endless papermaking As industrial papermaking evolved and developed, so did the importance and scope of water circuits as well Factors that have shaped and influenced this development are:

• A reduction in the specific water volume: As the specific water volume is reduced, the demands on the contaminant removal efficiency of the installed circulation water treatment rise, since the water must be used several times and fresh water is also replaced by

circulation water at critical locations This means that more water must be treated and higher requirements are placed on the treated water

• Development of production capacities: The increased productivity, which in some cases is considerable, makes it necessary to hydraulically adapt the elements of the water circuit

• Increased product quality and greater use of recovered paper: High requirements on water quality make it necessary to separate heavily loaded and slightly loaded water and the removal of components detrimental to the product The greater use of recovered paper significantly aggravates the above-mentioned conditions even more

• Greater raw material efficiency: This requires the collection and recirculation of all partial flows containing solids Only clarified water is discharged A system that is integrated into the water system must take over solids management

The requirements mentioned above result in practice in the construction of complex water circulation systems Their appearance, the mode of operation of the elements contained in them and possibilities for system closure were investigated in the SP1 In the related reports an in-depth analysis of the water quality requirements can be found

On the basis of waste water characterization and the defined water quality requirements in SP1 for paper mills, WP3.1 aimed at defining new treatment lines to reach the water quality target including effectiveness, reliability and minimization in waste and concentrate production These new treatment lines should be focused on internal recycling

Therefore a focus has been done on different key steps of the global treatment train:

- Biological treatment: anaerobic processes and MBR;

- Filtration processes: 3FM high speed technology and nanofiltration;

- Tertiary treatments to reduce hard COD: AOPs, coagulation/precipitation;

- Integration of processes (evapoconcentration, electrodialysis and softening) in the treatment line to:

o treat the concentrate streams containing calcium, sulphate, chloride, organics which can lead to salt accumulation in case of water loop closure, corrosion, scaling of pipes and showers in the production process The removal of CaCO3 is crucial in the last case

o minimize the waste production and enhance internal recycling

A state-of-the art of each of these technologies is done in following chapter

1.1.2 State-of-the-art of tested technologies within the study

1.1.2.1 Anaerobic technology

Since the early 1980s, anaerobic treatment of industrial effluents has found widespread application in the pulp and paper industry Several hundreds of installations are treating a large variety of different pulp and paper mill effluents Of 205 operating anaerobic installations for the treatment of industrial wastewater in e.g Germany around 75 plants are located in the pulp and paper industry

Most of the reactors rely on granulation of biomass (sludge pellets, sludge granules) Granulation allows for effective separation of hydraulic and solids retention times Pelletized biomass forms the so called anaerobic sludge bed which is flowed through in upward direction by the wastewater fed to the reactor bottom using an inlet distribution system Treated effluent is discharged at the reactor top after separation of biogas and sludge pellets in a three phase separator Some effluent may be recirculated to the inlet distribution system to adjust hydraulic upflow velocity in

the reactor compartment Consequently these reactors are named UASB reactors (upflow anaerobic sludge bed) EGSB reactors (expanded granular sludge bed) are a further development

of the UASB type The main difference is that EGSB type reactors are operated at much higher upward velocities (5 – 10 m/h compared to 0.5 – 1.5 m/h) and therefore higher recirculation rates The increased upward flow permits partial expansion of the sludge bed, improved mass transfer between wastewater and biomass as well as some wash-out of inert influent suspended particles (provided different settling velocities of biomass granules and suspended matter) Higher upward velocities lead to taller reactors (approx 15 – 25 m) compared to conventional UASB systems (5 –

8 m) For example there are 22 UASB-type installations and altogether 42 EGSB-type reactors of different manufacturers (DWA IG 5.1, 2009) in German Pulp&Paper industry In recent years EGSB-type reactors are almost exclusively built for the treatment of pulp and paper effluent Anaerobic treatment is most commonly used for effluents originating from recycle paper mills, especially during production of containerboard Moreover wastewater of mechanical pulping (peroxide bleached), semi-chemical pulping and sulphite and kraft evaporator condensates may

be treated The advantages of anaerobic pre-treatment are (1) net production of renewable energy (biogas), (2) minimized bio-solids production leading to reduced disposal of excess sludge, (3) minimal footprint because of high volumetric loading rate and (4) reduced emission of greenhouse gases (Habets and Driessen, 2007) Via in-line application of anaerobic treatment in closed circuits (paper kidney technology) further savings on cost of fresh water intake and effluent discharge levies may be generated

Some major prerequisites have to be fulfilled for successful application of anaerobic treatment technology in pulp and paper industry (see also chapter 1.1.1.2 above):

• Elevated temperature: In most cases the temperature optimum of mesophilic microorganisms (30°C - 37°C) is adjusted in anaerobic reactors Thermophilic conditions (50°C – 55°C) have been also applied in P&P sector and may be successfully used at existing elevated temperature of effluents (van Lier, 1996)

• Optimum pH: The pH in anaerobic reactors has to be kept at 6.5 ≤ pH ≤ 7.5 in the optimum range for methanogenic bacteria Fermentative bacteria my also proliferate at lower pH e.g in hydrolysis reactors or equalisation tanks

• Reduced suspended solids (SS) concentrations: High concentrations of suspended solids (SS) have to be removed before modern high rate anaerobic reactors, because SS may accumulate in the reactor and replace active biomass or prevent successful granulation respectively The acceptable solids load in the influent varies depending on reactor system and nature of solids (e.g fibre, inorganic solids) COD of organic SS should not exceed around 10 % of the total COD load (DWA IG 5.1, 2002)

• Sulphate toxicity: Effluents of P&P production are often rich in sulphates Reduction of sulphate will predominantly lead to generation of H2S, which is toxic for anaerobic bacteria

at certain concentrations, depending on reactor pH As reduction of sulphate also is energetically more favourable than methanogenesis, high sulphate concentrations in the influent to the anaerobic reactors will limit methane production COD/S ratio is the major governing factor At COD/S > 100 limitations are not to be expected, at COD/S < 50 inhibition may occur

• Precipitation products: Inorganic precipitates: - especially CaCO3 - will influence reactor performance Because of pH-shift in the anaerobic reactor precipitation will occur starting

at around 100 mg Ca2+/L As Ca2+ concentration in effluents of containerboard production may easily exceed 1000 mgCa2+/L heavy precipitation of CaCO3 has to be expected, which will lead to clogging and calcification of sludge pellets Selective removal of precipitates in-

or outside the anaerobic reactor has to be accomplished There are some technologies for

Softened water may be recycled to the anaerobic treatment in order to dilute Ca2+ concentrations

• Nutrient balance: Nutrient (N, P) and trace element concentrations (e.g Fe, Co, Ni, Se, W, Mg) for anaerobic processes have to be controlled regularly P&P wastewater usually is deficient in nutrients and trace elements Nutrient balance COD:N:P:S should be maintained at around COD:N:P:S ≈ 800-500:5:1:0.5 (DWA IG 5.1, 2002)

The first generations of the MBR were developed in 1960 They are based on side stream configuration, which is usually designed with tubular membrane They are operated under cross-flow conditions with a very high liquid velocity In this concept, the activated sludge is pumped into the membrane modules placed on the side of the biological tank resulting in high performances and high fluxes, but at significant energy consumption and a larger footprint Therefore this technology is preferred for difficult wastewaters and small-scale high strengths water application

Treated water

Figure 1: Side stream configuration

Submerged bioreactors (MBRs) have been developed in the middle of 1980s in order to simplify the use of these systems and to reduce operating costs In this configuration the membranes are immersed in a tank containing the biological sludge and the permeate water is extracted Air coarse bubbles are used to promote proper turbulences and circulation around the membrane modules They are designed with hollow fibres or flat sheet membranes

MBRs exist in two configurations In the inside configuration, membrane modules are immersed directly into the bioreactor In the outside configuration, membrane modules are placed outside the bioreactor A pump circulates the mixed liquor from the bioreactor to the membrane module or back at a flow rate of 100 to 500 % of the influent flow Advantages associated with the outside submerged MBR implementation are among others easier maintenance and cleaning, and higher operational flexibility This probably explains why outside submerged MBRs quickly became the favoured MBR design for municipal plants in Europe However, the inside configuration is strongly preferred for smaller plants, for flat sheet membrane applications

Treated water

Biological tank

Effluent

Sludge in excess

Treated water

Treated water

Treated water

Figure 3: Outside Submerged membrane bioreactor

There is currently growing interest in the MBR (membrane bioreactor) process in municipal and industrial wastewater treatment In the year 2007, Germany already boasted about 70 - 80 MBR facilities, 17 of which were in municipal wastewater treatment plants (Pinnekamp, 2007) Since

2007, three German paper mills have invested in this technology too, putting MBR plants into service Added up, this means that at the European level paper mills are currently operating at least nine MBR plants (Simstich and Öller, 2010) Generally speaking, the operating costs of the MBR process are still higher compared to the conventional version with a final clarifier (Möbius and Helble, 2007) If the costs are higher than those of conventional systems, what speaks in favour of this technology? The advantages for a use in the paper industry can be narrowed down

to the following three points (Judd, 2011):

• Sedimentation becomes a thing of the past: this means not only smaller space requirements but also the end to problems caused by bulking or floating sludge or sludge overflow in general

• Better effluent quality: solids and micro-organisms are retained, only dissolved substances and salts can pass through the membrane

• Higher sludge age and MLSS (mixed liquor suspended solids) concentration: this results in

a more compact construction and shorter hydraulic retention times being possible

MBR is used in the paper industry as end-of-pipe technology as well as process integrated measure for the reduction of the concentration of detrimental substances in the water circuit A typical problem of the membrane filtration of paper industry wastewaters is calcium scaling Calcium carbonate is used in paper production as filler and coating pigment Due to the common use of recovered paper as raw material, high concentrations of calcium can occur in the water circuit Especially mills producing board or corrugated paper typically have a nearly closed water circuit with low specific effluent volumes of << 5 l/kg paper This combination of dissolved calcium from the raw material and high process water reuse rates leads to high water hardness and problems with scaling and precipitation As filtration processes are susceptible to scaling problems, measures have to be studied to enable the successful use of membrane technologies

in the paper industry

Despite the challenge of the water hardness, the MBR technology was chosen in the project as it

for the industrial wastewater treatment But, however, precondition for a more common use is research on fouling and scaling if an application in the paper sector is considered

1.1.2.3 3FM technology

Tertiary treatment of secondary treated wastewater is the easiest way to improve first step in the direct reuse of water The filtration of water and wastewater plays indeed an important role within industrial water treatment lines and the removal of particles and sticky solids can be a major problem to implement a membrane process after a biological treatment, when speaking of recycling water The purpose of water filtration is to remove particles and colloids which either disturb the industrial process, deteriorate the quality of the final product or support bacteria and viruses that are a danger for human health

The conventional treatment generally consists of coagulation, flocculation, sedimentation and sand filtration One of the main disadvantages of this process combining sedimentation and sand filtration is the rather long residence time, mostly due to the flocculation and sedimentation phases Sand filters are as well used but though a good removal efficiency of particle including colloids, they need relatively low filtration velocities thus requiring a large installation area Although applied at full scale for pre-treatment before a following nano-filtration or reverse osmosis step, the performances of these pre-treatments is not as effective as that of MF and UF (Vedavyasan, 2007) Another disadvantage of the conventional pre-treatments is their relatively low filtration velocity (maximum velocity of 20 m/h)

A high rate fibre filter was then developed by Veolia Water STI and its high efficacy for the tertiary treatment of waste waters was proved in terms of high filtration velocity and good removal of particulate matter (Ben Aim et al 2004) The 3FM® system (Flexible Fibre Filter Module) is a new high speed filtration device that can be substituted for conventional solid-liquid separation process

such as coagulation, settling and sand filtration (Jeanmaire et al 2007; Lee et al 2008)

Compared with existing rapid sand filters, the 3FM filtration system has a velocity more than 10 times faster at 120 m/hr and has a smaller footprint, requiring up to 1/10th the space of sand filters Suspended solids are filtrated by flexible fibres in polyamide in a module, which have softness, elasticity and a degree of surface roughness These fibres have a three branch star shape and are not porous (Figure 4)

Figure 4: 3FM fibres

The filter is packed with bundles of fibres along the module length and influent flow is introduced

to the bottom of 3FM Utilising all of the filter area through deep bed filtration suspended solids particles are captured (Figure 5) The optimum operating parameters are managed according to the influent characteristics desired quality of the treated water

AIR (FOR BACKWASH)

REJECT (SLU DGE)

REJECT (SLU DGE)

Principle of 3FM filtration system:

Alternation of filtration periods and backwash

oFiltration process (
+  ): Service water is fed through the inlet pipe of the lower part of the apparatus and introduced uniformly into fibrous filter layer During the filtration process, SS are removed by the fibers and clean effluent water is discharged to upper part.

oBackwash process (
+  +  ): When inner pressure reaches predetermined value of pressure switch due to SS clogged

in the filtering process or time reaches predetermined value on the timer, the backwash process is initiated SS clogged

in the filter are remove in a short time by introduction of air which shake the fibers.

Although an innovative process, 3FM® operation is easy as a sand filter Head-loss increases during the filtration cycle and the filtration capacity is recovered by periodic backwashing with a small amount of influent waste water and scouring air (Figure 5) Backwash is generally operated every 3 hrs approximately (depending of inlet specifications) and needs less than 1% of the maximum treated water Main impact of 3FM is on TSS content in the water and thus on turbidity

as well A cut size of ~5-10 µm is obtained

Applicable fields are SS removal from sewage/WTTP, from industrial and agricultural water, water re-use, algae removal from river and reservoir, preliminary treatment of drinking water (Korea, China).This technology is currently used at industrial scale on several WWTP in Korea for

obtaining treated water of high quality (Ben Aim et al 2004) and has been applied as well as treatment to minimize the organic fouling of SWRO membranes used for desalination (Lee et al 2009; Lee et al 2010) Until now 3FM technology has never been applied as tertiary treatment to

pre-P&P waste waters

For more details regarding this technology and its industrial operation, refer to the report “D6.1.1 Knowledge and technological portfolio” and as well to internal report “I3.1.1.1 Proof of concept of aerobic water treatment technologies and separation techniques on bench scale for Pulp & Paper”

1.1.2.4 Membrane technologies (UF, NF, RO)

Membrane treatment in P&P-industry serves to optimize loop closure and therefore helps to reduce fresh water intake as well as wastewater treatment Other purposes of membrane processes are: improved product quality because of lowered pollution of loop water, re-use of treated effluent in production, recovery of valuable substances e.g coating pigments and minimizing environmental impact because of improved effluent quality (Simstich and Öller, 2007) Different types of modules have been use for NF in pulp and paper industry A wide range of spiral wound modules is commercially available, but also cross-rotational or vibratory shear enhanced modules were tested The latter two are basically circular flat sheet arrangements, where high shear or cross-flow is created through rotation or vibration (Nyström et al., 2005)

suspended matter has to be expected Spiral-wound modules are mostly installed in typical treatment configurations, when suspended and colloidal matter has been reduced down to very low concentrations in preceding treatment steps

post-Full scale membrane filtration of Pulp & Paper effluents has been already installed in some mills Nanofiltration treatment of total effluent was installed in a newsprint paper mill several years ago (Lien et al., 1995) Since no biological treatment had been installed, effluent was treated by physico-chemical pretreatment and several pre-filtration steps before NF in order to reduce fouling and clogging tendencies In a Finnish paper mill paper machine clear filtrate is treated with ultrafiltration using CR-filters (Metso Paper Chem Oy) and subsequent NF with spiral wound modules (Sutela, T., 2001) Nanofiltration with spiral-wound modules has been used for full-scale tertiary effluent treatment in one German mill producing newspaper from 100 % recovered paper

NF was chosen in order to reduce residual COD, AOX, colour and salinity for direct discharge or partial loop closure (Schirm et al., 2002) Another full-scale installation in Germany has been started up recently (2008) in the production of cardboard and packaging paper featuring a membrane bioreactor and reverse osmosis for the production of around 27 m³/h reclamation water for reuse in the mill (90 % recovery)

The advantage of NF in the recovery of water for recirculation is mainly that the clean water can

be used even in the most demanding places in the paper mill With NF, the COD reduction is

70 % – 90 %, the AOX reduction between 60 % and 97 %, most multivalent metals are reduced

by more than 90 % and colour is reduced for more than 90 % (Nyström et al., 2005, Schirm et al., 2002) A combination of UF-NF-RO was even used in a pilot system to produce reclamation water for the irrigation of crops in Australia (Cox et al., 2008) Drawbacks in the use of commercially available NF modules are the need for heavy pretreatment e.g the addition of chemicals for water conditioning, clarification and filtration for removal of suspended solids (sand, screen or bag filters, Mänttäri et al., 2006) In case of the German newspaper mill using NF two stages and filtration is used for pre-treatment MBR technology serves as modern alternative because of superior quality of UF filtrate A combination of MBR + NF / RO therefore seems promising for water recycling in pulp & paper industry, but there is lacking experience to name it a proven technology Recovery rates of up to 90 % – 93 % (volume concentration factor 10 – 15) have been reported for the NF treatment of biologically pre-treated effluents depending on wastewater load and membrane type (Mänttäri et al., 2006) Still the combination of membrane technology and high inorganic content - which remains present in pre-treated effluents of paper board mills - needs to be addressed in detail, since recovery rates and treatment costs are interconnected closely

Economic assessment of NF treatment of ground wood mill effluent water has shown, that depending on flux and pre-treatment associated cost for reclaimed NF permeate varied from around 0.9 €/m³ - 1.4 €/m³ Schrader (2006) estimates around 0.2 €/m³ - 0.6 €/m³ for the reclamation of NF permeate from municipal wastewater effluent, which is lower than for NF treatment of P&P effluents Cost for NF concentrate handling through incineration or hazardous waste disposal (subsequent to evapoconcentration and drying) varied from 5 €/m³ to 38 €/m³ (total cost referring to permeate volume at around 83 % recovery of permeate) Governing factor for economic feasibility of reclamation of NF permeate therefore are concentrate handling costs Consequently Schrader (2006) stated the need for a tailored concentrate treatment, which will also be assessed during pilot trials in this project

1.1.2.5 Ozone/AOP technologies

Today Ozone and UV are well known and proven in the field of water and waste water treatment – ozone as multifunctional powerful oxidant and UV as best available technique for disinfection regarding treatment results, plant design and cost (Ried, 2009)

techniques (e.g Fe/H2O2, TiO2/UV) are more in the focus of public interest and are studied for a

broader potential use (Sievers, 2011)

The main goal of these combined processes is to enhance the oxidation potential The reason for this enhancement is the increased generation of hydroxyl radicals, which have a higher oxidation potential (Glaze, 1987) It is known that hydroxyl radicals are almost twice as reactive as chlorine and its oxidation potential is close to that of fluorine (E = 2.32 V/NHE at pH=7) (Bigda, 1995) and they react very quickly with nearly all organic compounds Therefore this enhanced reaction leads

to better treatment results regarding advanced degradation and faster kinetics

Figure 6 gives an overview of possible pathways to generate hydroxyl radicals There are 4 main ways of using Ozone, UV, H2O2 and their combinations

3 2

1

Figure 6: O3 / UV / H2O2 - possible pathways (1- 4) for OH-radical formation

Possible pathways for hydroxyl radical formation:

1 Typical water compounds, e.g hydroxyl anions, iron ions or organic compounds can initiate/promote a decomposition of dissolved Ozone and generate hydroxyl radicals Consequently a part of Ozone reactions in waste water goes with generation of hydroxyl radicals without using any additional enhancement These highly reactive hydroxyl radicals usually initiate the oxidative destruction of organic substances (R) present in wastewater by

OH addition reaction or hydrogen atom abstraction (Huang, 1993) Organic free radicals (R) are formed as transient intermediates and are further oxidized by other intermediates to form stable, oxidized products (Huang, 1993)

2 Different oxidized species will be generated during the UV radiation of Ozone molecules in water The typical wavelength for this process is 254 nm The molar extinction coefficient,

Depending on the generated intermediates, e.g excited oxygen atoms (O), hydrogen peroxide (H2O2) or the conjugated base of H2O2 (HO2-), there are different further pathways (a-c) for hydroxyl radical generation In practice there are more than these three mentioned pathways So the Ozone/UV process is very complex It is not really possible to describe exactly all chemical reaction details or the kinetics and the hydroxyl radical yield

3 In the presence of hydrogen peroxide Ozone reacts with the conjugated base of H2O2 to form hydroxyl radicals

4 The UV radiation of H2O2 leads directly to the formation of hydroxyl radicals From the stoichiometric yield (1 mol H2O2 → 2 mol OH radicals) this process is the most efficient But the molar extinction coefficient for the wavelength 254 nm is only 19 mol-1

cm-1

For a given UV-radiation this low coefficient leads to a much lower OH-radical yield than the Ozone/ UV process (20 times higher) One way for compensation is to use high concentrations of H2O2

(> 10 mg/l) Moreover it is possible to work with wavelengths in the range of 200 to 250 nm to improve the molar extinction coefficient Therefore, typically, a medium pressure UV-lamp is used But, in that case the required energy input becomes the limiting factor compared with other AOP`s

Applying advanced oxidation processes AOPs

Combined chemical (AOP) and biological oxidation processes have a well-known potential for

removing recalcitrant and anthropogenic substances from wastewater e.g., Scott and Ollis, 1995,

reviewed 58 publications – mostly based on lab scale studies – and identified four different types

of wastewater contaminants which can benefit from combined processes:

1) Process streams containing high concentrations of recalcitrant compounds;

2) Biodegradable wastewaters with small amounts of recalcitrant compounds;

3) Inhibitory compounds;

4) Intermediate dead-end products

Additionally the decolourisation with ozone has already been established as an application of polishing of biological treated effluents

The positively synergistic effect of process combination is based on the enhancement of the biodegradability of such compounds by chemical oxidation (ad 1, 3, 4) and the need of polishing

of biologically treated effluents (ad 2) (i.e.: Balcioglu, 2007; Bijan, 2008; Chang, 2004; Mounteer, 2007)

Complete oxidation of organic compounds is usually not economically feasible because large amounts of energy and chemicals are necessary Direct oxidation and the enhancement of COD degradability compared to the untreated sample are crucial for total COD elimination (Simstich, 2010)

In general the following items are important when using AOPs:

- the potential yield of hydroxyl radicals;

- amount of radical scavengers;

- the required energy input;

- plant design;

- investment and operational cost

Consequently, the application of AOPs for the treatment of retentates coming out from membrane treatments of pulp and paper industries must mainly take into account i) the influence of wastewater composition (these waters are usually high organic loaded and they have high values

of alkalinity and chlorides that could reduce the efficiency (De Laat, 2004)), ii) the efficiency of the process and iii) as well as the economic study

In practice a high amount of so called scavengers, e.g carbonates might quench hydroxyl radicals So the generated radicals are not available for the treatment process itself In real waste waters further possible pathways exist for radicals to react without increasing the treatment result significantly Due to this complexity of real waste waters in practice pilot trials have to prove the best technique (Acero and Gunten, 2001; Ternes et al., 2001)

What do we know so far?

a) Ozone based oxidation

Ozone can oxidize other compounds in two different ways: directly reacting with dissolved compounds, or indirectly via hydroxyl radicals produced in its decomposition (Esplugas, 2002) Due to the short half-life of ozone, continuous ozonation is required to keep the process going on This is one of the major drawbacks of the treatment, considering the cost of ozone generation (Catalkaya, 2007; Kreetachat, 2007; Ried, 2009) Furthermore, reactivity of ozone is also affected

by the presence of salts, pH and temperature (Catalkaya, 2007); and the process efficiency is highly dependent on efficient gas-liquid mass transfer

The combination of ozone with hydrogen peroxide (O3/H2O2) is considered a promising alternative

to remove refractory organic chemicals from wastewaters (Masten, 1994) HO2− (conjugate base

of H2O2) at millimolar concentrations can initiate the decomposition of ozone into hydroxyl radicals much more rapidly than the hydroxide ion (Catalkaya, 2007), therefore the addition of hydrogen peroxide produces a faster ozone degradation (Gogate, 2004a; Mounteer, 2007, Ried, 2005) Ozonation is a successful method to oxidize chemicals present in wastewaters from pulp and paper mills, such as eugenol, cathecol, phenol, trichlorophenol and cinnamic acid derivatives The double and triple bonds of lignin compounds that produce the colour of paper industry wastewater are easily oxidized by ozone (i.e.: Kreetachat, 2007; Öller, 2009) Moreover, ozonation usually increases biodegradability of paper mill effluents by toxic compound degradation and changes in molecular weight fractions from HMW to LMW (Amat, 2005; Balcioglu, 2007) Two large-scale ozone plants are operating successfully in paper mills in Germany and Austria (Schmidt et al., 2000; Kaindl, 2009) for the tertiary treatment of wastewater

Conducting systematic laboratory tests is recommended with the scope of meeting the envisage target values in each case, as the structure of the organic compounds present in the effluents is very important in terms of oxidation by ozone or other AOPs Oxidation by ozone as a standalone technology is considered as impractical for pulp and paper mill effluents and may not offer sufficient removal and mineralization of organics (Bijan, 2008) However using ozone oxidation to get partial oxidation of organics and enhance its biodegradability is more feasible (Bijan, 2008; Tuhkanen 2002) An interesting possibility is to use a biological or membrane treatment to separate the HMW fraction, avoiding the unnecessary oxidation of the LMW organic fraction (Bijan, 2008)

b) Fenton method

Fenton method is one of the most common and efficient AOPs for wastewater treatment Moreover, it usually implies a lower capital cost than other AOPs (Esplugas, 2002; Tang, 1996; Krichevskaya, 2010) It is based on the electron transfer between H2O2 and Fe2+, which acts as a homogenous catalyst to yield hydroxyl radicals (OH·) that can degrade organic compounds (Harber, 1934), as it can be expressed by:

Typically, Fenton treatment is performed in the following four stages (Bigda, 1995): pH adjustment, oxidation reaction, neutralization-coagulation, and precipitation (centrifugation); whereas organic substances are removed by both oxidation and coagulation pH is one of the major factors limiting the performance of the Fenton process It is optimum between pH 2.5-3 due

to a higher solubility of iron and a higher stability of hydrogen peroxide (Hermosilla, 2009a) Moreover, the effectiveness of the Fenton method is directly related to the amount of hydroxyl radicals formed, which is function to the concentration of hydrogen peroxide and the amount of ferrous ion available

Fenton treatment has two important drawbacks: the acid pH and the production of iron sludge, which requires ultimate disposal (Pignatello, 2006) In order to diminishing the production of iron sludge, the modification of the conventional Fenton process by the combined application of UV-light has been suggested

The photo-Fenton process has two major features: (a) the reduction of ferric to ferrous iron, producing additional hydroxyl radicals via photolysis (Kavitha, 2004), i.e.:

c) Photocatalysis using a catalyst semiconductor (TiO2)

New tendencies are focused in the UV assisted AOPs with reusable catalysts, such as TiO2

(Yeber, 2000) These treatments imply the irradiation of a semiconductor (e.g TiO2, ZnO) with UV light at a wavelength shorter than 390 nm (Yeber, 2000) Heterogeneous photocatalysis employing TiO2 and UV light has demonstrated its efficiency in degrading a wide range of

ambiguous refractory organics via creating an electron-hole pair, whereas photogenerated “holes”

may react directly with organics and charge carriers might migrate to the surface where they react with adsorbed water and oxygen to produce radical species that attack any adsorbed organic molecule and can, ultimately, lead to complete decomposition into CO2 and H2O (Ahmed, 2009) Pérez (2001) reported that the heterogeneous photocatalytic process catalyzed by titanium dioxide (UV/TiO2) efficiently removes colour and dissolved organic carbon (DOC) from ECF bleaching effluents and lignin containing solutions A rapid decrease of toxicity in different solutions was also reported by different authors (Catalkaya, 2008; Perez, 2001; Yeber, 2000) and the enhancement of biodegradability shows that photocatalytic systems may be an interesting pre-oxidation step preceding biological treatment (Yeber, 2000)

In pulp and paper industry, flocculation is involved in different parts of the process: it is essential

to form the paper sheet in the forming wire, determining retention, drainage rate and the formation, and it is also used in the wastewater treatment to separate the colloidal material and in the sludge thickening

Factors, that affect the flocculation process and that are related to the flocculent, are nature, structure, molecular weight and charge density of flocculent However, flocculent dosage and polymer chain conformation are also critical factors (Ordoñez, 2009) In addition, many different chemical aids can be used to induce flocculation process In this project, different polyaluminium

anionic and a cationic polyacrylamide (aPAM and cPAM) have been used as dual systems to induce the flocculation of colloidal material

The study and control of the flocculation or coagulation process is carried out by monitoring the evolution of the particles chord size distribution on real time, which is obtained by a Focused Beam Reflectance Measurement technique (FBRM) and contains information about the size and concentration of the particles in the dispersion, whose variation is the image of the flocculation process for all the flocculation mechanisms (Blanco, 2002)

The FBRM technique implies the use of commercial Mettler Toledo equipment with a probe, which

is entered into the suspension or into the pipe, and an electronic box with a detector (Figure 1) A computer system controls the equipment and receives the data This equipment has a laser diode which emits a laser beam divided in different parallel rays that are focused on a focal point on the external sapphire probe window (sited in the extreme of the probe that is introduced in the suspension) through a rotating lens The focal point describes a circular path at high speed because of the rotation of the rotating lens When a particle intercepts with the focal point path, the light is reflected and conduced to the detector, which receives light impulses, whose duration

is proportional to the chord length of the particle that has intercepted the focal point path (Figure 1).The equipment can measure thousands of particles per second and thus, obtain a chord length distribution that represents the particle population

Figure 7: How the FBRM probe works

This technology is applicable to study any flocculation process, independently of the aggregation mechanism or the suspension nature The traditional methodologies, based on the measurement

of the surface charge of the particle, are appropriate to study the aggregation process only when

it implies the modification of these properties, but not when the flocculation is carried out by other mechanisms, as bridging with neutral polymers, for example (Blanco, 1996; Blanco, 2002)

One of the main advantages of this methodology developed by UCM is that it does not require manipulating the suspension before using it Most of the optical techniques used to study the flocculation process require the previous manipulation of the suspension, to dilute or to adjust pH

or ionic strength, because many of them are based on measuring turbidity or on image analysis, being useful only if the suspension is diluted enough to allow the pass of the light, as in the dispersion photometric analyser, for example Furthermore, these techniques assume that the turbidity or the colour of the suspension does not change and/or that the particles are spherical The FBRM methodology has been used on-line to control flocculation process in the pre-treatment of fresh water used in refrigerating towers, in a Hatschek machine that produces fibre cement, in the headbox of a paper machine (as part of the European project: RODET-QLK5-CT-2001-00749) and in the fed to the first cylinder sieve of a board machine (as part of the European project: SHAKER-COOP-CT-2004-032352) When this technology is used for controlling flocculation, it is possible to detect any alteration in the process before it affects the downstream and, because of that, it possibilities to carry out the pertinent action in the most efficient way

Evaporation involves the removal of water from the solution by boiling the liquor / effluent in an evaporator (see Figure 8) The generated vapour is usually removed and condensed as a distillate, while the non-volatile phase remains liquid as a concentrate, which is rich in dissolved products

Condensate

The aim of evapoconcentration is to obtain a very clean distillate which could be rejected in

the nature, sent in a sewage treatment plant or reused The concentrate is considered as an

ultimate waste usually disposed to landfill or which can be incinerated as well

When the solution to concentrate is rich in salts, the enrichment of the liquid phase can exceed the saturation limit and a crystallized solid phase appears

Evaporator design consists of three principal elements as shown in Figure 9 (Minton, 1986) The heat transfer takes place in heating units or calandrias: in most cases the solvent is water The vapour-liquid separations take place in a vapour-liquid separator called bodies, vapour heads, or flash chambers Finally, the circulation of solute assures the thermal transfer and the evaporation

For efficient evaporation, the selected equipment must be able to accomplish several things:

- Transfer large amounts of heat to the solution with a minimum amount of metallic surface area This requirement, more than all other factors, determines the type, size, and cost of the evaporator system

- Achieve the specified separation of liquid and vapour and do it with the simplest devices available, while using efficiently the available energy

- Meet the conditions imposed by the liquid to be evaporated or by the solution to be concentrated Factors to be considered include product quality, salting and scaling, corrosion, foaming, product degradation, hold-up, temperature sensitivity, and the need for special types of construction

Salting, scaling, and fouling result in steadily diminishing heat transfer rates until the evaporator must be shut down and cleaned Some deposits may be difficult and expensive to remove: it is thus very important to reduce deposition (Minton, 1986)

Evapoconcentration needs a great heat transfer, on one hand to heat the solution up to boiling temperature and then to assure the phase transfer It is essential to find the industrial conception which enables the great compromise between energetic and investment cost considering characteristics solution

Concentration of solution by solvent evaporation is carried out in single or multistage evaporation units with or without thermal or mechanical vapour compression, or in multistage flash evaporation units The most used conceptions and their characteristics are presented in the Annex 8.1

Evaporation has proven to be a very efficient and reliable technology for treatment of industrial waste-water mainly due to its flexibility in the treatment of very different types of wastes, with a very high load of pollutants (Cox, 2007) Evaporation is applied, for example to:

- The treatment of exhausted oil emulsion and die casting waste-waters producing a condensate that is re-used in the preparation of new emulsions

- The treatment of effluents from surface treatments, e.g the plating industry (chrome plating, zinc plating, etc…), degreasing, tumbling waters, pickling solutions, regeneration eluates from resin demineralisation plants, etc., (LIFE Zero Plus, 2007)

- The concentration of leachates and exhausted solutions from landfill and effluent disposal centres

- The treatment of printing waste-waters containing ink, glue, etc., and waste-water from flexo printing etc

- Several different applications in the chemical and pharmaceutical industries;

- Power plants with zero liquid discharge (ZLD) for the treatment of reverse osmosis concentrate and resins eluates from demineralisation plants, or from desulphurization processes

- Pulp & paper industry for the removal of inorganics

In most applications the condensate produced (treated stream) is recycled to the working process, thus achieving the status of Zero Liquid Discharge If recycling is not possible as for instance in landfills, the condensate can be discharged In some cases it is also possible to reach the ZTD when the concentrate is recovered An example is the electrolytic tinning for industrial packaging (mainly in food industry) where the tinning bath becomes diluted from carry over of water by the washed parts to be treated in the bath Evaporation continuously removes water thus maintaining the concentration of the bath constant The evaporated water can be used as wash water for prior treatments before tinning

- The reduction of the remaining solution volume, which generates a reduction of the

disposal costs It is characterised by the volume concentration factor (VCF) which is

defined as the feed volume divided concentrate volume

- The wide range of effluents which can be treated: this property is very interesting in the cases of industrial effluents which composition varies in time Whereas strong pH variations make bacteria involved in biological treatment die (loss of biomass), and the change of compounds can completely foul a membrane, evapoconcentration is much less sensitive to these changes

However, contamination of the distillate may happen when volatile compounds are present in the feed and foam, corrosion and fouling have to be controlled

In addition, evapoconcentration has high energy consumption (from 15-500 kWh depending on the applied technology): for this last reason, evapoconcentration is only focused on concentrated streams

Considering these, evapoconcentration has been applied within AquaFit4Use to the treatment of membrane concentrates in order to remove inorganics to produce high water quality water for re-use purposes and to reduce the final amount of wastes to be disposed of

1.1.2.8 Electrodialysis

Electrodialysis is an electrochemical membrane separation technique for ionic solutions that has been used in industry for several decades It can be used in the separation and concentration of salts, acids, and bases from aqueous solutions, the separation of monovalent ions from multivalent ions, and the separation of ionic compounds from uncharged molecules It can be used for either electrolyte reduction in feed streams or recovery of ions from dilute streams Industrial applications encompass several industries and include the production of potable water from brackish water, removal of metals from wastewater, demineralization of whey, deacidification

of fruit juices, and the removal of organic acids from fermentation broth (Krol, 1969) Additional examples of the applications of electrodialysis are given in Table 4 (Farrell, 2003)

Table 4: Industrial applications of electrodialysis

Potable water from brackish waterNitrate removal for drinking waterBoiler water, cooling tower water, effluent steam desaltingCheese whey demineralization

Fruit juice deacidificationSugar and molasses desaltingPotassium tartrate removal from wineBlood plasma protein recoveryDemineralization of amino acid solutions in the food industryAcid removal from organic products

Edible salt production from seawaterAg(I) salts from photographic wasteZn(II) from galvanizing rinse waterOrganic salts from fermentation brothAmino acids from protein hydrolysatesSalts, acids, and alkali from industrial rinse watersConversion of organic salts into acid and base (bipolar membrane ED)Salt splitting

As a selective transport technique, electrodialysis uses an ion-selective membrane as a physical barrier through which ions are transported away from a feed solution An energy intensive phase change is unnecessary, in contrast to the common separation techniques of distillation and freezing The use of an organic solvent, as is often required with other selective transport techniques such as liquid extraction, is avoided with electrodialysis In addition, electrodialysis is typically performed under mild temperature conditions, making it particularly attractive for food, beverage, and pharmaceutical applications that deal with heat liable substances

The principle that governs electrodialysis is an electrical potential difference across an alternating series of cation and anion exchange membranes between an anode and a cathode The feed solution containing both positive and negative ions enters the membrane stack to which a voltage

is applied, thus causing the migration of the ions toward their respective electrodes The cation exchange membranes allow the transfer of cations but inhibit the transfer of anions Conversely, anion exchange membranes allow the transfer of anions but inhibit the transfer of cations The result is alternating compartments containing streams of dilute ion concentration (diluate) and streams rich in ion concentration (concentrate) exiting the stack An ionic rinse solution is circulated past the electrodes to maintain conductivity of the membrane stack while preventing potentially corrosive ions from the feed solution from contacting the electrodes

This concept is illustrated in Figure 10 with a feed solution of a salt (C+A-) in aqueous solution The electrodialysis membrane stack comprises electrodes and membranes separated by gaskets and spacers The spacers are turbulence-promoting support mesh used to create the compartments through which the solutions flow Uniform flow distribution and prevention of internal leakage through spacer and gasket design are critical to system performance

Figure 10: Electrodialysis principle

Within the project, this technology has been tested in view of removing salts from membrane concentrates in order to enhance the water recycling into the biological treatment and prevent thus salts accumulation in the waste water’s treatment processes

1.1.2.9 Softening and controlled precipitation technologies

In industry, especially in the Pulp and Paper, the removal of scaling compound, especially calcium carbonate, is a key point in the perspective of a re-use of the wastewater: the recycling of water can indeed induce salt accumulation and thus scaling issues

Generally, the physicochemical treatment of wastewater from industrial operations (softening, acid waste neutralization …) typically involves chemical precipitation of the contaminants via acid-base neutralization (or other means) followed by separation of the solids from the solution

The precipitation reaction, core of the chemical engineering in such processes, is generally a very unstable mechanism when poor homogenization and dispersion of the reagents are applied in the reactor The consequences are:

- Lower removal efficiency (hydraulic short-cut, long induction time);

- Over-consumption of reagents (poor dispersion around the reagent input);

- Scaling on walls and pipes / residual TSS in treated water (post precipitation);

- Low density sludge presenting a high moisture rate (nucleation >>> growth)

Moreover, the size, shape, and density of the precipitated particles can have a significant impact

on sludge rheology, settling rate and dewatering performance In turn, these properties can affect the efficacy of solid recovery and/or recycle of these by-products

According to crystallization theory, precipitation is defined as reactive crystallization This

definition is preferred as it emphasizes the formation of the solid product via a chemical reaction The correlation of the precipitation processing conditions to product properties is determined via

the study and control of the following aspects of the process (Figure 11):

- Solid-liquid equilibrium;

- Crystallization kinetics, i.e super saturation, nucleation and growth;

- Colloid surface chemistry, i.e the aggregation of particles and the adsorption of impurities;

- Reactor selection and design (Demopoulos 2009)

Figure 11: A new paradigm for aqueous precipitation research (G.P Demopoulos, 2009)

To ensure and satisfy the quality of sludge produced, full attention to all these issues is then critical importance

Spanos and Koutsoukos (1998) studied the impact of the solid sowing on the reduction of induction times during the precipitation of calcium carbonate The induction times decrease with increasing super saturation while the rates of precipitation increase Moreover, it may be observed that the induction times are sufficiently shorter in the seeded precipitation experiments where the precipitation rates are higher especially at high super saturations

Figure 12: Initial rate of precipitation as a function of the mass of the added solid Total calcium

(Spanos and Koutsoukos, 1998)

From another side, Nason and Lawler (2008) described the influence of the solid sowing on the processes of softening During precipitative softening, particle size distributions are shaped by three simultaneous processes: homogeneous nucleation, precipitative growth, and flocculation The individual and relative rates of these three processes are strongly influenced by the saturation ratio, the seed concentration and the mixing intensity Increase in the initial seed concentration prevent (or delay) the formation of new, small particles by homogeneous nucleation

Figure 13: Heterogeneous calcite precipitation rate as a function of seed surface area at 25°C

Concerning the impact of reactor design on particle size distribution, the solids produced in conventional precipitation processes generally have a low median particle size (D50) and wide particle size distribution (PSD) compared to more advanced precipitation processes A low D50 manifests itself as sludge that is difficult to settle and dewater and may exhibit undesirable pseudo plastic or Bingham plastic tendencies This can negatively affect the efficacy of recycle from a practical process or operational perspective and be deleterious to the quality and composition of the recovered solids in general

Most precipitation processes are positively impacted (size of particles, reduced post precipitation, increase of precipitation kinetics, etc.) by increasing solid content (sludge recirculation) Indeed, in

the treated effluent can be problematic Calcium carbonate scaling is commonly observed Processes that include solids recirculation back to the point of neutralization can reduce or totally eliminate scaling because the increased surface area fosters secondary nucleation and reduces the level of calcium carbonate (and other constituent) super saturation (Barbier et al 2010, as shown in Figure 14)

Full post-precipitation avoided

Figure 14: CaCO3 post precipitation comparison measurement on in clarified softened water after neutralization tank on Multiflo process – impact of reactor design and solid ratio (Hard water composition : 80-100 ppm Ca & 130-170 Total Alkalinity - hard water softened to pH 10.5 with

lime – Turbidity monitoring with time)

To solve such problems, advanced precipitation and crystallization processes were developed that address the science of particle formation and growth to improve the recovered solids properties

a) Multifo-softening technology (Veolia)

Veolia has developed and used advanced precipitation processes (Cook 2003; Prokop 2006) with

sludge recirculation (Barbier et al 2009) including forced-circulation, draft-tube crystallizers with

custom mixers that yield very high circulation to minimize supersaturated zones Internal design of the Turbomix reactor improves solid particle homogenization which allows operating at higher mineral load and reaches high solid/liquid ratio in the reactor

Veolia Water Solutions & Technologies developed new high rate softening processes: ActifloTM

Softening and MultifloTM Softening (Figure 15) (i.e Chemical precipitation of hardness, alkalinity, silica and other constituents (e.g., heavy metals) for water production and wastewater reuse by the addition of lime, carbonate ion, metallic salts, polymer and recycled sludge

Turbomix reactor

These high rate precipitation processes combines within a single treatment line:

- A dynamic mixing stage for chemicals injection;

- An enhanced precipitation reactor with TurbomixTM system to improve reaction kinetics of chemical inputs;

- A conventional lamellar settling unit that removes the suspended matter;

- A sludge recirculation system that allows the re-injection of sludge in the crystallization chamber

Compactness is in addition one of the main advantages of high rate softener:

Conventional precipitation softening

Figure 16: Comparison of process compactness

Thus the challenge for high rated softeners is based on enhanced reaction zone (reactor) satisfying at the same time the abilities of a Continuous Flow Stirred Tank Reactor (CFSTR) for liquid and solid phases while minimizing energy input necessary for mixing As the reactor is well mixed, the total crystal surface area can be increased by increasing the slurry concentration (recirculation)

Within the project, this technology has been tested in view of removing scaling compounds before membrane processes (NF, UF, RO and MBR) in order to prevent scaling of the membranes and thus enhance recovery rates of the membrane processes This last one can generally be evaluated by measuring the Silt density Index (SDI) of the waste water Therefore scaling

simulation programs for scaling potential such as ROSA (Dow Company) and JChess (Armines, France) Furthermore silt density index (SDI) and turbidity give a general insight on suitability of the pre-treated waste water for membrane filtration

b) Filtration Assisted Crystallization Technology (TNO)

Filtration Assisted Crystallization Technology (FACT) is a hybrid process, patented by TNO, combining heterogeneous crystallization and a simple filtration step The heterogeneous seeds should allow both fast crystallization and easy filtration

The principle can be applied in aqueous solvents and organic solvents to remove hardness and other salts

The heterogeneous seeds grow during the FACT process until the moment that they have sufficient size and are separated A relatively small amount of heterogeneous seeds (about 1 g/l) create a significant increase of the crystallization kinetics, while at the other hand the use of seeds allows a compact and cheap filter for the S-L separation The type of the seeds, the concentration, the residence time and the pH are important parameters, as shown in Figure 17:

No seeds Seed 3 Seed 5 Seed 1 Seed 4 Seed 2

Figure 17: Comparison of the effect of various seed

material for CaCO3-removal in a laboratory test

Figure 18: Pilot to be tested in

Paper industry

Advantages in paper industry are the following:

- Closing of water cycles (and saving energy for heating water);

- Product (= seeds + CaCO3) can be used as filler, resulting in ± 25-50% reduction of raw filler material;

- More efficient use of cationic additives in the wet section (due to low [Ca2+] );

- Small volume and footprint, because of relative fast reactions;

- Competitive to conventional techniques like the pellet reactor

The FACT technology will be tested at another paper industry (SAPPI); the results will be reported

in D3.2.2 “New technology for removal of hardness, tested at pilot scale in location”

1.1.2.10 Biodegradability experiments

Biodegradability screening tests are a basic tool for the assessment of treatment alternatives for wastewater and the evaluation of pre-biological treatment steps (e.g oxidative) applied to bio-recalcitrant residual water There are several methods for evaluating biodegradability; among others, different bioassays have been used to assess detoxification, as the inhibition of the

luminescence of Vibrio fischeri bacteria (Pérez-Estrada et al., 2007); there are mixed methods that aim to evaluate toxicity and biodegradability, e.g Pseudomonas putida test measures the

biocompatibility of this micro-organism present in activated sludge, studying its growth in a solution (García Ripoll et al., 2009) Other methods focus the study of the behaviour of activated sludge micro-organisms, such as several methodologies that evaluate respiration rates of bacteria trying to provide a rapid screening method to assess the effects of substances on the micro-organisms present in activated sludge (OECD, 2009) An increase in the biodegradability of the sample has been also measured using biological oxygen demand (Guhl and Steber, 2006), or other methods aiming to simulate biological treatment conditions in standardized situations, such

as Zahn–Wellens test (EPA, 1998) This test is commonly used to determine the inherent biodegradability of a substance under biological treatment conditions, and it provides more useful information than just determining the BOD/COD ratio, toxicity, or testing respiration rates, although it implies a greater analytical effort and time to be performed (28 days); whereas 5 days are required for BOD5, some hours for respirometry or toxicity tests, or about 36 h for P putida

test

1.2 Objectives

The objectives of the work described in this report were:

- The identification of the best suitable new water technologies to reduce environmental impacts by advanced closure of the water cycle and produce the required water quality for re-use in the Pulp&Paper sector;

- Minimizing the waste production by testing new technologies to increase recycling, treat the concentrates and separate salts (membrane separation, evapoconcentration,….) in order to propose optimized treatment lines (efficient, reliable, cost effective);

- To define the best use of AOP’s by comparison of full stream and concentrated stream ozonisation

to be reused

Aerobic Process MBR

to be reused

Aerobic Process MBR

Softening

Figure 19: Global treatment line

On the basis of waste water characterization and the defined water quality requirements for paper mills, these new treatment lines were defined to reach the water quality target including effectiveness, reliability and minimization in waste and concentrate production These new treatment lines are focused on internal recycling

The emphasis was on different key steps of the global treatment train:

- Biological treatment: anaerobic processes and MBR;

- Filtration processes: 3FM high speed technology and nanofiltration;

- Tertiary treatments to reduce hard COD: AOPs, coagulation/precipitation;

- Integration of processes (evapoconcentration, electrodialysis and softening) in the treatment line:

o To treat the concentrate streams containing calcium, sulphate, chloride, organics;

o To minimize the waste production and enhance internal recycling

2.1 Methods

Technologies were tested at lab scale on the waste waters from 3 different paper mills:

• Paper mill 1 (PM1), producing corrugated board and board;

• Paper mill 2 (PM2), producing high quality coated and uncoated board from recycled paper;

• Paper mill 3 (PM3), producing standard news print, improved news print (higher brightness) and lightweight coated paper (for magazines)

2.1.1 Paper mill 1 (PM1)

Paper mill 1 (PM1) annually produces 230.000 tons paper for corrugated board and 83.000 tons

of board The specific water consumption of the mill is 3.8 m3/t board and 2.3 m3/t corrugated board Freshwater consumption amounted to 1800 m3/d The wastewater (1080 m3/d) is treated in the mill’s own treatment plant Part of the biologically treated water (240 m3/d) is reclaimed in the water cycle and 850 m3/d is discharged The following sketch shows the WWTP of PM1

Dissolved Air Flotation

Hydrolysis

Anaerobic Reactor

Capacity 1 2 t ons CO D/ d ay

Biogas Tank

Desulfurization

Final Sedimentation Tank

Dissolved Air Flotation

Hydrolysis

Anaerobic Reactor

Capacity 1 2 t ons CO D/d ay

Biogas Tank

Desulfurization

Final Sedimentation Tank

Figure 20: WWTP of paper mill 1 (PM1): Process flow diagram and image

Main treatment steps and related figures are:

- Two-step anaerobic-aerobic wastewater treatment plant;

- About 100.000 PE (population equivalent);

- Anaerobic reactor with internal circulation (IC reactor);

- Three-stage activated sludge tank with denitrification stage;

- Overall COD elimination efficiency: 95 %;

- Biogas quantity: 4.500 m³/d

The following table shows the main parameters:

AOP (O 3 )

MBR

NF

Impact of reinjection into anaerobic process ?

Evapo Water to be re-used ?

AOP (O 3 ) Biodeg.

tests

Possibility to reinject into biological processes ?

Water to be re-used ?

AOP (Fenton)

Biodeg.

tests

Possibility to reinject into biological processes ?

Water to be re-used ?

Water to be re-used ?

AOP (O 3 )

MBR

NF

Impact of reinjection into anaerobic process ?

Evapo Water to be re-used ?

AOP (O 3 ) Biodeg.

tests

Possibility to reinject into biological processes ?

Water to be re-used ?

AOP (Fenton)

Biodeg.

tests

Possibility to reinject into biological processes ?

Water to be re-used ?

Water to be re-used ?

Figure 21: Tests carried out on Paper mill 1 waste waters

The water quality requirements for re-use purpose were not clearly defined by PM1 Therefore, the targets considered in the above experiments for re-use were the ones described in the Internal result 1.2.2.1 “Description of required water quality in 4 sectors of the industry”, which are more general valid for paper industry and very well adjusted to a “typical” mill

Main treatment steps and related figures are:

- Two-step anaerobic-aerobic wastewater treatment plant;

- About 100.000 PE (population equivalent);

- Anaerobic UASB reactor with recirculation;

- Two-stage activated sludge tank with pre-denitrification stage;

- Overall COD elimination efficiency: 96 - 97 %;

- Biogas quantity: 3000-5000 m³/d

Figure 22: WWTP of PM2 - Process flow diagram and image of paper mill

Table 6: Characteristics of PM2 waste waters

More detailed water requirements for re-use purpose at PM2 are presented in table below:

Table 7: Water quality criteria for re-use purpose at PM2

Quality of

reclamation water

LOW quality (misc dilution)

MEDIUM quality (spraying nozzle)

HIGH quality (white paper grade)