Luận Án tiến sĩ development of an appropriate treatment system for natural rubber industrial wastewater treatment

11 Table 1.2 National technical regulation on the cffluent of the natural rubber Table 1.3 Type of treatment process applied in Vietnam [4] - - 12 ‘Table 1.4 Application of UASB reacto

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCLENCE AND ‘TECHNOLOGY

Takahiro Watari

DEVELOPMENT OFAN APPROPRIATE TREATMENT

SYSTEM FOR NATURAL RUBBER INDUSTRIAL

WASTEWATER TREATMENT

CITEMICAL ENGINEERING DISSERTATION

Hanoi — 2022

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF SCLENCE AND ‘TECHNOLOGY

Takahiro Watari

DEVELOPMENT OF AN APPROPRIATE TREATMENT

SYSTEM FOR NATURAL RUBBER INDUSTRIAL

1 Assoc Prof Nguyen Minh lan

2 Prof ‘lakashi Yamaguchi

Hanoi — 2022

ACKNOWLEDGMENT

Virstly, | would like to thank the Professors and Staff in the Ph.D program,

and the officers im the Department of Education, Hanoi Universily of Science and

Technology Thank you for all the guidance and support you have made for me

while | fulfilled the dissertation

Working with colleagues in the Department of Chemical Engineering has

been a privilege I would like to thank you from the bottom of my heart for your

conslanL encouragement

Finally, I am so glad to have a supervisor like Assoc Prof, Nguyen Minh

Tan Ever since I started to work under your supervision, I have learned a lot which

helps me lo become a betler person Tharik yout You are the best supervisor ever

| hope to receive some words of encouragement and full support from the

readers to make my Ph.D dissertation better

Hanoi, 26 Dee 2032 Author of the dissertation

‘Takahiro Watari

DECLARATION

1 hereby certify that the dissertation "Development of an appropriate

treatment for industrial rubber industrial wastewater treatment" is my research

project, The data and results stated in the doctoral dissertation arc honest,

| hereby declare that the information cited in the doctoral dissertation has been fully originated /

Hanoi, 26 Dec 2022

E.1.1 Natural rubber processing, process

1.1.2 Natural rubber processing wastewater

1.2, Current treatment technology for natural rubber processing, wastewater 1.2.1 Biological aerobic and anaerobic pond

1.2.2 Upllow anaerobic sludge blanikel reactor

1.2.3 Anaerobic baffled reactor

1.2.4 Activated sludge process

1.2.5 Swim bed †8Rk cọ họ Họa

1.2.6 Downflow hanging spOnge reactOr co

1.3.7 Dissolved air floafation ni is

1.3.8 Memibrane bioreagOF n0 egerree

1.2.9 Combbinod Ireatmert systems [or natural rubber processing wastewater

1.3 Industrial wastewater treatment process

1.3.1 Characteristics of anaerobic wastewater treatment and the degradation

patluway of anacrobic digostion

1.3.2 Anacrobic industrial wastewater treatment technology

1.3.3 Characleristics of aerobic waslewaler trealment and the degradation

1.4 Greenhouse gas emissions from the wastewater treatment system

2 Material and methods

iti

m

ví

ví

2.2.2 5ystem description and operaional conditiors — -

2.3.1 Raw natural rubber processing wastewater - - 35 2.3.2 System description and operational conditions - - 35 2.4 Pilot UASB-DHB systeim nen neerieree 36

2.5.10 Iiogas production and cornposition eccee AD

3.1 Characterization of a current wastewater treaiment system - Az

3.2 Performance evaluation of a laboratory-scale UASB-DHS system for

natural rubber processing wastewater treatmeni SO 3.3 Performance evaluation of a laboralory-scale ABR experiment 37

3.3.2 Determinates profiles inside the ABR - - 59

3.4 Performance evaluation of a pilot scalc UASB-DHS system oxperiment for

iv

treatment of natural rubber processing wastewater

61 3.4.1 PfoCess pGTÍOTHADGÔ cá sọ bọn re _— 61 3.4.2 Nitrogen removal and greenhouse gas emissions « 66 3.4.3 Performance comparison of ABR-UASB-DHS system and existing

treatment syStOM eee sscccecissssuessessesssveessesessssessssseeessenessssevansssnsseesseee 70

Figure list

Figure 1.1 Top natural rubber-produced countries over the world in 2020-2021 [3]

5 Figure 1.2 Natural rubber harvested area and production in Vietmam [2] 6 Figure 1.4 Natural rubber manufacturing proeess [S] " Figure 1.5 Schematic diagram of the coagulation process [5] ¬

Figure 1.6 Full-scale biological pond in Victuram ¬-

Figure 1.8 Various reactor configurations of ABR [16] 18 Figure 1.9 Basic water flow in conventional activated sludge 19 Figure 1.10 Principle of downflow hanging sponge reactor and full-scale DITS in

lẽ Figure 1.11 Development history from DH5 G1 to DH8 G6 [36) 21 Figure 1.12 Anacrobic digestion scheme of organic compounds 25 Figure 1.13 Acrobic biological degradation pathway 27 Figure 2.1 Schematic diagram of open-type anaerobic system - 29 Figure 2.2 Gas sampling system used in this stuổi co 31

Figure 2.3 (A) Thanh Hoa Rubber Factory, (B) Coagulation process in natural

rubber sheet producing process cucsesesneensessnensennnensmennaenenanvnsnnenne dE Figure 2.4 Schematic diagram of the baffled reactor (BR), upflow anaerobic

sludge blanket (UASB), and downflow hanging sponge (DHS) combaned system (1) Substrate reservoir, (2) pump, (3) pretreatment tank, (4) pump, (5-9) sampling ports, (10) UASB column, (11) Gas solid separator, (12) mixer, (13) heated water cohunn, (14) water bath, (15) desulfurizer, (16) gas meter, (17) distributor 34 Figure 2.5 Protocol for preparation of natural rubber processing wastewater

following actual factory tuethods, cào 38

Tigurc 2.6 Schematic điagram of anacrobic bafflcd reactoi

Figure 2.7 Schematic and photo of the pilot scale ABR-UASB-ST-DHS system 38

vi

Figure 3.1 Biogas composition of compartments 28, 33, and 56 48 Figure 3.2 Methane gas emission rate and COD concentration of cach

Figure 3.4 Nitrous oxide rate and ammonia concentration in cach compartment 49

Figure 3.5 Composilion of smitled GHGs from near the influent part, the center part, and the effluent part of the OAS - 30

Figure 3.6 Tỉme course of pÏT and temperature đurïng the operation periods 53 Figure 3.7 Time course of (a) total COD, (b) soluble GOD, (e) T8S, (đ) V35, and

(e)'TN durïng the operation periods «co nưec Khen 55

Figure 3.8 COD mass balance of the influent, BR effluent, and UASB effluent

during phase 2

Figure 3.9 Time course of (A) Total COD and (B) TSS concentrations through

Figure 3.10 Soluble COD, acetate, and propionate concentrations in ABR on (A)

Figure 3.11 Accumulation of rubber particular in feed pipe and photo of

'WAS(@WA{€TS u cung ng Hàn ¬— <

Figure 3.12 Time course of (A) Total COD remeval clfieiency mủ orgarie loading rate of TASB reactor, (B) Tolal BOD removal elficioncy, 65 Figure 3.13 (A) Total nitrogen and (B) ammonia removal efficiency of the total system and DHS reactor during phase 1 to phase 4 69

vii

Table list

Table 1.1 Characteristics of natural rubber processing wastewater in Victnam 11 Table 1.2 National technical regulation on the cffluent of the natural rubber

Table 1.3 Type of treatment process applied in Vietnam [4] - - 12

‘Table 1.4 Application of UASB reactor for natural rubber processing wastewater

T68EHEHE cueieeiieeieeerrriee HH HH kg hd tt nhe sneer EG

‘Table 1.5 Comparison of technologies used for natural rubber processing

wastewater IOBLIHONL, .ccceecscccisssseseerissesseeeensensssttenssserttnsvessetin ste 23

Table 1.6 Benefits of the anacrobic treatment process

Table 1.7 Application of anaerobic technology to industrial wastewater [33] 27 Table 1.8 Global warming potential of GHG: ce BB Table 2.1 Water quality of natural rubber processing wastewater obtained from a

natural rubber sheet-producing factory in Thanh [Toa Provinee 33

‘Table 2.2 Summary of the initial operational conditions for the two operating phases

Table 2.4 Initial operational conditions through phases | to 4 39 Table 3.1 Present treatment system flow of a local natural rubber processing factory

‘fable 3.2 Water quality in each sampling point at a local natural rubber processing 'wastowater in Vietnam LH Hee oi _— Table 3.3 Summary of process performance of the treatment system Số

Table 3.4 Surmary of the process parameters of the sysiem durïng entire

Table 3.5 Biogas production and compositions of the UASB reactor 65

Table 3.6 Nitrogen concentrations (mg-N'L”) in the proposed system 6

‘fable 3.7 Characteristics of natural rubber processing wastewater in Thailand,

Malaysia, and Vietiam ccieihoiehirrrreerree ¬—-

Table 3.8 Process performance of the existing treatment system for treating natural Tubbôr PFOGE35ing, WASE@WAEET, án cọ re Keeeeee.f

ix

Abbreviations words list

ABR Aerobic baffled reactor

BOD Biochemical oxygen demand

cL Concentrated latex

cob Chemical oxygen demand

DAF Dissolved air Dotation

DUS Downflow hanging sponge

GWP Global warming potential

TIRT Hydraulic retention times

MBR Membrane bioreactor

OAS Open-lype anaorobi

OLR Organic loading rate

ORP Oxidalion-reduction potential

1N 'Yotal nitrogen

TSR Technically spccificd rubber

‘TSS ‘Total suspended solids

UASB Uptlow anaerobic sludge blanket

VPA Volatile fatty acids

vss Volatile suspended solids

Abstract

Natural rubber is one of the most valuable agricultural products in

Southeast Asian countries Vietnam is the 3 largest natural rubber-producing

country, and natural rubber production in Victnam is increasing cach year However, the natural rubber industry discharges large amounts of wastewater containing high

concentrations of organic compounds, nitrogen, and other contaminants from several wmanufackotmg processes such as coagulalion, centrifugation, lammation,

washing, and drying The natural rubber processing factories in Southeast Asian countries commonly use a combined anaerobio-aerobic lagoon system for treating natural rubber processing wastewater because of the low installation costs ‘Ihe existing treatment systems have been demonstrated to achieve a high chemical oxygen demand (COD) removal elficiney of 6Š Lo 909% with casy operalional

methods However, they require a large area for the lagoon, high operating costs

(especially for surface aeration), and long hydraulic retention times (ARTs)

Tawever, the effluent water quality of these existing treatment systems needs to be improved to conform to the established discharge standards

An upflow anaerobic sludge blanket (UASB) reactor is one of the most promising systems for the treatment of different types of industrial wastewater because of ils high organic loading rale (OLR), low operational cosls, and energy recovery in the form of methane Previous studies have reporled the applieation of

the UASB reactor for the treatment of natural rubber processing wastewater However, it was determined that natural rubber particles remaining in the

wastewater had a negative effect on the anaerobic biological process ‘herefore, the development of a pre-treatment system to remove the remaining natural rubber partioles is essential Moreover, when a UASB reactor is used to treat high-strength industrial wastewater, the effluent still conlains high concentrations of organic

compounds and nutrients Thus, an aerobic treatment system 1s Lypieally applied as

a post-treatment to remove residual organic matter and meet effluent standards A downflow hanging sponge (DHS) reactor is one of the most effective aerabie

treatment systems applied as a post-treatment with the IASB reactor to treat

different types of industrial wastewater,

Objective

Current wastewater treatment systems used to troat natural rubber

processing wastewater in Victnam consume a large amount of electrical onorgy and

have a large negalive impacl on the environment Ta this study, we characterized the process performance (e.g., waler quality and biogas emission) of the current

wastewater treatment system and developed an enerpy-recovery type advanced wastewater treatment system to reduce greenhouse gas (GIIG) emissions and improve the effluent quality resulting from the treatment of natural rubber

processing wastewater

Tasks {Scientific and practical meanings)

1) Survey of the current wastewater treatment systems used to treat natural rubber processing wastewater at some typical rubber factories in Vietnam

To investigate the current situation of natural rubber processing wastewater at some typical rubber factories in Viemam, the water quality of the existing wastewater treatment systems was determined by field surveys and journal paper surveys In addition, the GHG emissions from an existing anaerobic lagoon werd measured to determine the environmental impact of global warming

2) Development of an energy-recovery lype waslewalcr Ircalmont system

The UASB-DHS system has been applied to treat domestic sewage and several types of wastewater In addition, the UASB-DHS system was successfully

applied in ‘Thailand to treat natural rubber processing wastewater, which contained a high concentration of sulfuric acid In this study, we examined the application of the

UASB-DHS system for treating natural rubber processing wastewater in Vietnam

and cvalualed ils process performance al the laboratory scale and in a pilot-seale

experiment

3) Establishment of a new treatment system that is superior to previous ones to treat

natural rubber processing wastewater at some typical rubber factories in Vietnam

The discharge amount of industrial wastewater in Vietnam is expected to increase each year A conventional activated sludge process is usually applied to treat industrial wastewater in developed countries, but the installation, operation, and maintenance of this type of system are very expensive The UASB-DHS system

wo developed is known to be an cnergy-recovery and energy-saving wastewater

treatment system and has been applied to several types of wastewaler If the application of the JASB-DHS system lo natural rubber processing waslewaler iv

Vietnam is successful, it could reduce operational casts and GIIG emissions and improve the effluent quality Moreover, this advanced wastewater treatment technology can be applied to not only natural rubber processing wastewater but also

other industrial wastewater emitted in Vietnam

Current Problem and its solution

The discharge amount of industrial wastewater in Vietnam is expected to increase

each year

A conventional activated sludge process is usually applied to treat industrial wastewater in developed countries, but the installation, operation, and maintenance

of this type of system are very expensive

‘The UASB-DHS system we developed is known to be an energy-recovery and

energy-saving wastewater trealmen| system and has been applied to several types of wastewater

TỶ the application of the UASB-DHS system to natural rubber processing

wastewater in Vietnam is successful, it could reduce the operational costs and GHG emissions and improve the effluent quality Moreover, this advanced wastewater treatment technology can be applied to not only natural rubber processing

wastewater but also other industrial wastewater emitted in Vietnam

1 Overview

1.1 Natural rubber

Rubber is widely used in industry and can be categorized as natural rubber and synthetic rubber Natural rubber consists of polymers of the organic compound isoprene, with minor impurities consisting of other organic compounds and water:

3

Natural rubber has good wear resistance and high elasticity, resilience, and tensile strength It has a good dynamic performance and a low level of damping ‘Iherefore, natural rubber has been widely used for carpet underlay, adhesives, foam, balloons, and medical accessories such as rubber gloves [1] On the other hand, synthetic rubber is produced trom coal oil Synthetic rubbers are more resistant to oil, certain

chemicals, and oxygen and have better aging and weathering characteristics and

good resilience over a wider Lemperature range Both natural rubber and synthetic

rubber can be used properly according to the application, but they are combined like automobile tires The total amount of rubber consumed in 2017 reached 28,287,000 tous, and this was a 3% increase compared with the amount consumed in 2016 over the world in 2017, the amount of natural rubber produced increased to 13,380,000 tons Thailaud and Indonesia produce over 60% of the lolal amount of natural rubber (Figure 1.1)

Vietnam is the 3 largest natural rubber producer in the world and produced

1,094,500 tons in 2017 [2] The quality of the natural rubber produced and the harvested area in Vietnam have increased each year (Figure 1.2) The rubber tree is

grown mostly in the Binh Phuoc, Binh Duong, ‘Tay Ninh, and Dong Nai provinces

in the Southeast region of Vietnam because of ther favorable climate and suitable land for the optimal growth of rubber trees (Figure 1.3) The optimal growth

conditions for rubber trees are as Follows:

Rainfall of around 250 em that is evenly distributed without any marked dry season and with at least 100 rainy days per year

‘Temperature range of about 20 to 34°C, with a monthly mean of 25 to 28°C

Atmospheric humidity of around 80%

About 2,000 hours of sunshine per year at a rate of 6 hours per day throughout the

year

Absence of sirong winds

4787 Indonest

Harvested

area (ha)

200,000 100,000

Southern Highlands Central region Northern

Figure 1.3 Natural rubber production area in Vietnam [2]

Production (ton)

1.1.1 Natural rubber processing process

Natural rubber is harvested mainly in form of the latex from the rubber tree (1ievea brasiliensis) or other trees Iigure 1.4 show the production process for

rubbor products in a natural rubber processing factory [4]]5| Latex is a sticky, milky colloid that is obtained by making an incision in the bark and collecting the

fluid in vessels in a provess called “lapping.” Raw nalural rubber lalex is collected

from a rubber bree, and ammonia is immediately added to keep i al a high pH to

prevent coagulation Anti-coagulation measures are especially necessary under wet weather conditions and with lattices that have a strong tendency for pre-coagulation

‘Therefore, the amount of anti-coagulant used during the wet season is higher than that used in the dry season Nguyen (1999) noted that the amount of ammouia that should be added Lo latex to prevenl malural coagulation depends on the season [6] Wet season: 1.0— 2.0 kg:tons dry rubber” (0.1 — 0.2% wet weight)

Dry season: 0.5-1.5 kg-tons dry rubber (0.05 - 0.15% wet weight)

The amount of ammonia also depends on the distance from the collection site to the processing factory

After it is transferred to the factory, natural rubber latex is first filtered through a mesh screen to removed collated mibber, particles, leaves, and other

matenal Then it is diluted with fap waler Acids such as acetate or [formic acid are added to coagulale it ito a natural rubber block (Figure 1.5) The coagulated

natural rubber is pressed to make a rubber sheet and smoked in a furnace Finally, the rubber sheet is washed with tap water and dried in the sun

‘Phe products of natural rubber latex are manufactured in a local factory into three types of raw rubber sheets: technically specified rubber (TSR), concentrated latex (CL), and ribbed smoked sheet (RSS) TSE is graded in a quality

mspection afler iL ia formed TSR is also called “blocked rubber” or “erumb rubber”

because of ils morphology TSR is the most widely used type in the US and Buropean countries RSS is a smoked rubber sheet and is largely used in industry

Tapping

GHG Diesel ———+ Transportation + Emissions

Sodium bisutfite Fresh water Standardization

+

Bleaching agent Coagulation | serum}

Figure 1.4 Natural rubber manufacturing process [5]

Diluted latex Acetic/formic acid

|]

Acid

Figure 1.5 Schematic diagram of the coagulation process [5]

1.1.2 Natural rubber processing wastewater

The main products from local natural rubber processing factories are CL

and RSS The production processes for these products such as coagulation, centrifugation, lamination, washing, and drying use a large amount of fresh water and discharge the same amount of wastewater In Vietnam, surface water and

groundwater are mostly used A previous study reported that in Vietnam 25 m’ of

wastewater is discharged from the production of 1 ton of RSS from fresh latex,

whereas approximately 18 m? of wastewater is discharged to produce 1 ton of CL

[7] This wastewater is heavily polluted, and it is causing environmental problems

because of insufficient wastewater treatment [8] The characteristics of natural

rubber processing wastewater are very different between the RSS and latex production processes Table 1.1 summarizes the effluent quality of natural rubber

processing wastewater in Vietnam Nguyen (2003) surveyed 27 rubber processing factories in five provinces and summarized the quality of their effluents [4] These wastewaters mainly contained wash water and small amounts of uncoagulated latex

and serum with small quantities of proteins, carbohydrates, lipids, carotenoids, and salts The wastewater discharged from the CL producing process is the most

polluted wastewater compared to other wastewater because this wastewater contains

high concentrations of uncoagulated rubber particles and organic matter [7] The

COD and total suspended solids (TSS) in latex wastewater are approximately

9

20,000 mg'L™ and S00 mg-L", respectively The wastewater discharged from

factories producing standard Vietnamese Rubber (SVR) rubber sheets is acidic (e.g,

pli 4.8-5.S), The main organic compounds in this natural rubber processing wastewater arc volatile fatty acids (VFAs) Acctate and formic acid have been widely uscd for ficld latex coagulation in Vietnam Specifically, the natural rubber

processing wastewaler collected from the coagulation process ala rubber processing,

mg-COD-L" acetate and 4,500 me-COD-L” propionate [9]

Both CL wastewater and SVR wastewater contain a high concentration of

ammonia (e.g., 100 mg-N-L" to 1,000 mg-N-L™) Ammonia is added to the latex in

the tapping cups and collecting buckets to imerease the pH of the latex to prevent premalure coagulation The amount of ammonia added to latex to prevent natural

coagulation depends on the season and the distance from the collection site to the processing factory [10] The wastewater from CL factories contains a high concentration of nitrogen

The industrial effluent discharge standards for environmental protection are usually provided by the government Natural rubber processing wastewater is one of the Jargest sources of industrial wastewater pollution in Southeast Asian

countries, and usually, specific and strict, effluent slandards are established for natural rubber processing factories Tr Vietnam, the Ministry of Natural Resources and the Environment provides national technical regulations for the effluent of the natural rubber processing industry (QCVN 01-MT: 2015/BTNMT) The Vietnamese

effluent standards for water quality are shown in ‘lable 1.2, Standard A is applied for effluent discharged into the domestic water supply (used for daily activities, except directly for drinking and cooking) Standard B is applied for other water supplies

other than the domestic waler supply (c.g., waler larisport, uTigakion, aquaculture, cultivation) The national technical regulations published im 2015 contain two

categories: new factories (started operation after 31/March/2015) and existing factories (started operation before 31 /March’2015)

10

Table 1.1 Characteristics of natural rubber processing wastewater in Vietnam

1 ‘Type of product, Ceumb Som cig fomlewer saeds NR 3 Latex Si sR n

Bota ine Tap

TƯ Ni nhan Rulber

Table 1.2 National Lechnical regulation on the ¢ffluent of the teatural rubber

processing industry in Vietnam

1.2 Current treatment technology for natural rubber processing

wastewater

As mentioned above, natural rubber processing wastewater contains large amounts of organic compounds and nitrogen In addition, unbiodegradable natural

rubber particulates remain in the wastewater, and thus, the wastewater treatment

syslem tieeds io remove these rubber particulates Currenily, several types of wastewater treaimenL systems have been applied for natural rubber processing

wastewater treatment (Table 1.3) In natural rubber producing countries such as

Southeast Asian countries, low-cost wastewater treatment systems for treating this

type of wastewater are desirable ‘I'he effluent treatment processes in use in Vietnam were surveyed by Nguyen (2003) [4] Aerated lagoons and ponds are commonly used for dhe treatment of this waslewaler On the other hand, the application of advanced treatment processes such as dissolved air flotation (DAF) and a TASB

reactor has been limited Therefore, simple, natural processes such as the bialogical

pond method have been widely applied

‘Table 1.3 ‘Type of treatment process applied in Vietnam [4]

Type of treatment proc:

No ofapplying factory

1.2.1 Biological aerobic and anaerobic pond

The bictogicat pond (lagoon system) is commonly used for the treatment

of natural rubber processing wastewater in Southeast Asian countries (I'igure 1.6)

12

More than 500 anaerobic biological ponds have been installed in Malaysia for palm

oil and natural rubber processing factories [11][12][8][13] With this system, it is

possible to achieve a high organic removal efficiency with low operational and

installation costs The oxidation ditch process (aerated lagoon) is the most popular treatment system for natural rubber processing wastewater in Vietnam [4] In this system, usually, 2, 4, or 6 units are arranged in series, parallel, or both and equipped with surface floating type aerators Ibrahim (1980) demonstrated the possibility of achieving efficient ammonia nitrogen removal in a laboratory-scale experiment [14] Currently, this process is combined with a rubber trap and/or anaerobic lagoon, and

the final effluent water meets the effluent standard or water quality stated in

Vietnamese Standard B [7][15] However, a local factory consumes a large amount

of electricity for wastewater treatment, higher even than the amount used for natural

rubber production [15] In addition, GHG emissions from the oxidation ditch

process are of concern because of the low dissolved oxygen (DO) concentration and

low C/N ratio in natural rubber processing wastewater

Figure 1.6 Full-scale biological pond in Vietnam

1.2.2 Upflow anaerobic sludge blanket reactor

AUASB reactor is one of the most promising systems for the treatment of different types of industrial wastewater because of its high OLR capacity, low

operational costs, and energy recovery in the form of methane [16] The formation

13

of well-settleable sludge aggregates and the application of a reverse funnel-shaped internal gas-liquid-solids separation (GSS) device are key technologies for a

successful UASL reactor (ligure 1.7) ‘he characteristics of the UASB are listed

below

1) The influent is fed from a bottom reactor to create up-flow

2) Tf the UASB reactor is correctly operated, granulalion can occur and result inthe formation of high setlealslity sludge in the reactor

3) The UASB reactor has high contacting efficiency because of high biogas production

4) ‘The washed-out sludge is effectively collected by the GSS

5) ‘There is 90% less excess sludge from the UASB seactor compared with that from an activated sludge process

Table 1.4 summarizes the process performance of the ASB reactor when

treating natural rubber processing wastewater The first application of a UASB

reactor for the treatment of natural rubber processing wastewater in Vietnam was demonstrated by Nguyen (1999) in his Ph.D research at Wageningen University [6] The results showed that the UASB reactor performance achieved around 79.8% 87.9% of total COD removal efficiency at an OLR of 28.5

kg-COD-m"- day" However, the remaining natural rubber particulates, such as

accumulated Tubber particulates in the UJASB column, affected the anaerobic biodegradation Therefore, an effective pre-treatment process to remove residual natural rubber particulates is required for the application of UASB reactors in Vietnamese local natural rubber processing factories Nguyen et al (2016) reported that the granulation was enhanced with the use of aluminum chloride, and the total COD removal efficiency of the UASB reactor increased to 96.5 + 2.6%, with a methane recovery rate of 84.9 + 13.4%, for natural rubber processing wastewater in Vietram |17|

The UASB technelegy for natural rưbber processing wastewater treatment

is actively researched in Thailand, the country that produces the most natural rubber Jawjit and Liengcharernsit (2008) investigated the treatment performance of a

14

two-stage UASB reactor applied to CL processing wastewater [10] The results indicated that the UASB reactor achieved a high process performance when the pH

was controlled at 7 and operated under mesophilic conditions (35°C) on a

laboratory-scale level Tanikawa et al (2016) examined a pilot-scale two-stage

UASB reactor (volumes of 997 L and 597 L, respectively) in the Von Bundit natural

rubber processing factory in Sra Thani, Thailand [18] The system achieved a COD

removal efficiency of 95.7% + 1.3% at an OLR of 0.8 kgCOD-m*:d" Bacterial

activity measurement in the retained sludge from the UASB revealed high activity

of sulfate-reducing bacteria (SRB), especially hydrogen-utilizing SRB, compared with that of methane-producing bacteria In addition, the recovered methane from the two-stage UASB reactor can completely recover the electricity needed for the operation of the two-stage UASB-DHS system

Figure 1.7 Schematic diagram of UASB reactor

(http://www acs-environment.com/en/reactor-types/uasb-reactor)]

Table 1.” Application of UASB reactor far natural rubber processing wastewater

treatment

Reacior ype Velume Sesdsludge Organicremovalraie COD removal

Digested pig

Singie Vielnam 855 manure sludge 288 79.8-87.9% Nguyen (1995)

Anaercbic

digester trating casava Single Vielnam 17 wastewater 285 965226 Thess ota {205

Concentrated Two stage Thailand 248 141 82 and Liengcharemr est /2U101

‘Two stage Thaland 997 +597 factory 98 9657213 la toa zLal, (2018)

1.2.3 Anaerobic baffled reactor

An aerobic haffled reactor (ABR) has been designed since the early 1980s

and has several advantages aver a well-established system such as a UASB reactor

and anaerobic filter [16] These advantages are better resilience ta hydraulic and organic shock loadings, longer biomass retention times, lower sludge yields, and the ability to partially separate the various phases of anaerobic catabolism ‘Lhe most significant advantage of the ABR is the typical reactor configuration that can separale acclogen and methanogen longitudinally down the reactor This two phases operation can onhance acctogen and methanogen activity by a factor of up to four as

acetogen accumulates within the first stage, and the different microbial groups can develop under more favorable conditions Therefore, the ABR has been applied to the treatment of various industrial wastewater summarized advantages associated

with the ABR are shown below:

generation; 3) High solids retention time; 4) Retention of biomass with fixed media or solid-settling chamber, 5) No special gas or sludge separation required

Operation

1) Low HRT; 2) Intermittent operation possible; 3) Extremely stable to hydraulic shock loads; 4) Protection from toxic materials in influent; 5) Long operation

times without sludge wasting; 6) High stability lo organic shock

Figure 1.8 shows various reacor configurations of ABR Since ABR was proposed,

several types of reactor configurations were designed The first report of ABR was equipped with several partitions in the reactor to keep a high concentration of methanogens ‘this study reported the methane recovery rate was increased to 30 ~

55% in OLR of 1.6 kg-COD-m?-day™[16] Figure 1.8 (A) is a basic design of ABR

that is vorlically separated by the wall Figure 1.8 (B) iwslalled a chamber Lor

settling and a gas sampling line in each compartment for improvement of the

retention time of waste solids In Figure 1.8 (C), the diameter of the downflow compartment made narrow, and the increased sludge retention time in the up-flow compartment

Alanna and Clark (2000) reported the performance of a granular-bed anaerobic baffled reactor (GRABBA) applied in the treatment of whisky distillery wastewater

[17] The GRABBA used granular sludge for inoculation snd il can be compatible with both advanlages of the UASB reactor and ABR

For the treatment of natural rubber processing wastewater containing a large amount of rubber particulars, this specific reactor configuration of ABR is one of

the promising treatment systems for recovering natural rubber particulars from wastewater In fact, several natural rubber factory has applied small ABR as pre-treatnent of natural rubber provessing wastewater and acted as an efficient

tubber particle recovered system

Figure 1.8 Various reactor configurations of ABR [16]

1.2.4 Activated sludge process

An activated sludge process is commonly used for sewage and industrial

wastewater treatment worldwide There is a large variety of designs, however, in

principle, all activated sludge processes consist of three main components: an

aeration tank, which serves as a bioreactor; a settling tank (“final clarifier”) for the

separation of solids and treated wastewater in the activated sludge, and a retum

18

activated sludge apparatus to transfer the settled activated sludge from the clarifier

to the influent of the aeration tank (Iigure 1.9) Atmospheric air is introduced into a mixture of primary treated or screened sewage combined with organisms to develop

a biological floc This acration process requires a huge amount of electricity The acration tank retains the floc that contains 2,000 ~- 5,000 mg'L"' bacteria The main

bacterial groups in Lhe aeration tank are the phyla Pseudaminas, Bacillus, Microbacteramm, Acinelobacter, and Nocardia In addition, Protozoa and Meiasoa

grow in the aeration tank, resulting in high microbial diversity in this ecosystem with an extremely long food chain The settling tank is installed for the separation

of effluent and the floc ‘the activated sludge process can be widely applied to low- and middle-strength industrial wastewater Nguyen (2002) reported that the aclivaLcd sludge process can achieve removal cfliciencies uf 52% for COD and 25%

for Total Kjeldahl Nitrogen in natural rubber processing wastewater treatment with

Oxygen Retemed sludge

Figure 1.9 Basic water flow in conventional activated sludge

1.2.5 Swim bed tank

‘The swim-bed technology, involving a novel aoryl-fiber biomass carrier fringe, is a new approach to wastewater treatment, especially for the high-rale treatment of organic waslewaler Nguyon el al (2012) examined a lahoralory-scale swim-bed technology for latex wastewater and found good organic removal and

nitrification at an OLR of 1.0kg -m* day [4]

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1.2.6 Downflow hanging sponge reactor

A DIS reactor is a trickling filter that uses a sponge as the medium (igure 1.10) In 1997, the group of Prof Llarada and collaborators first developed a sponge-based bioreactor, as a novel cost-cffcctive post-treatment method for anacrobically pre-treated sewage |18] Many research papers on the performance of

DHS reactors for treatingy sewage have been published [19-27] To date, six types of spouge carriers have been proposed and their process performance demonstrated [19] The most promising post-treatment system is a conventional aerated tank

because an aerated tank can provide a high effluent quality with superior organic and nitrogen removal efficiencies However, the process requires a large amount of electricity for oxygen supplementation and produces large amounts of excess sludge Algal tanks have also boon applicd (o teal effluent from the anacrobic tank

treatment of natural mibber processing wastewater [20] This system efficiently removes organics and nitrogen, but it requires a long HRT and a large treatment

area, as da conventional aerated tanks

Figure 1.11 presents a summary of the sixth sponge carriers developed for DHS seactors Currently, the G-3 type sponge is widely used because of its high process performance ‘he highlight of the DHS reactor is that it can be operated without avralion or with low acration requirements, #8 oxygen is naturally dissolved

in waslewater In addition, the sponge media supporl a large ammount of biomass as

well as high microbial diversity on the surface and in the inner section of the sponge media, The high microbial diversity in this ecosystem with an extremely long food

chain reduces the production of excess shidge [29-32] Tandukar et aL (2007) reported that the volume of excess sludge produced from a combined UASB DHS system was 15 times lower than that from a conventional activated sludge process [22] The DHS reactor has been spplicd for the treatment of several types off

industrial waslowatcr, especially the post-treatment of UASB reactorirealed

high-strength industrial wastewater [23][24] Several studies have reported the treatment of molasses wastewater using a UASB-DHS system [34-36] Moreover, the DLIS reactor has been applied to treat reactive dye wastewater [26], freshwater

20

aquariums [27] [28], and ethylene glycol-containing industrial wastewater [29]

Figure 1.11 Development history from DHS G1 to DHS G6 [30]

1.2.7 Dissolved air floatation

The DAF process clarifies wastewater by removing suspended solids such

as oils and solids This process has been widely used in treating industrial wastewater from oil refineries and petrochemical and chemical plants In addition,

the DAF process is used to remove unicellular algal blooms and for supplies with

21

low turbidity and high color for drinking water treatment In natural rubber processing wastewater treatment, the DAI process can achieve a high removal efficiency of suspended solids, but the high cost of this process prevents its wide application [7]

1.2.4 Membrane bioreactor

A membrane bioreactor (MBR) combines a membyane process such as

microfillralion or ultrafiltration and a biological wastewaler tealment, process such

as an activated shndge process The application of an MBR for natural rubber processing wastewater has been demonstrated by Sulaimanal et al (2010) [31] The

MBER system at a flux of 0.009 m’m™”-h" achieved better removal efficiencies than

an oxidation ditch for all parameters

Au anacrobic membrane biorcaclor (AnMBR), which combmes an

anaerobic process and membrane technology, is considered a very appealing

alternative for wastewater treatment because of its significant advantages over

conventional anaerobic treament AnMBR can achieve a high OLR of 12.7 kg

m?-day" for latex serum treatment together with methane recovery [31] All MBR

applications for natural rubber processing, wastewater have only been demonstrated

at the bench scale Therefore, a full-scale MBR application for natural rubber

processing wastewaler is expected

1.2.9 Combined of treatment systems for natural rubber processing

wastewater

Table 1.5 summarizes the wastewater treatmem technologies for natural rubber processing wastewater Lach process has advantages and disadvantages l'or

natural rubber processing wastewater treatment, several wastewater treatment

systems are combined to meet effluent standards A decantation tank is usually used

im almost, all processing faclorics as a post-treatment lo temove the remaining

natural rubber particulates in the wastewaler system The combination of aa anaerobic tank and oxidation ditch process has been widely used for natural rubber

processing wastewater treatment in Southeast Asian countries This process has a

simple structure and cheap construction costs Several natural rubber processing

22

factories have installed a UASB reactor instead of an anaerobic lagoon

‘Yable 1.5 Comparison of technologies used for natural rubber processing

Organic removal High

dao đợc tạp g2) THSh — Tgh above 0% Low Tigh

Alkstany requirement 1y lew Madee Lew Taw Tow Law

Ty Low Moderde High Modeule Moderule © Moderte Modmẻe Stat uptime — Low Moderue High Mịnh Maderde Modede Modmée Bioenergy and

recovery

1.3 Industrial wastewater treatment process

1.3.1 Characteristics of anaerobic wastewater treatment and the

degradation pathway of anaerobic digestion

Anaerobic digestion is a fermentation process in which organic material is

degraded, and it produces biogas containing methane and carbon dioxide ‘This biodegradation occurs in many places where organic material is available under

anaerobic or anoxic conditions Anaerobic digestion is a more attractive wastewater ireatment process than acrobie wastewater trealment processes, Anaerobie wastewater Ireatrneui can effectively remove biodegradable organic compounds, leaving mineralized compounds such as NH,' and PO,° in the solution The

bioreactor for an anaerobic wastewater treatment process is a very simple system and can be applied at any scale and in almost any place ‘Ihe main benefit of the

23

anaerobic wastewater treatment process is that useful energy in the form of methane can be recovered In general, 40 ~- 45 m° of biogas can be recovered from 100 kg-COD of influent [32] In addition, an anaerobic wastewater treatment process can reduce the large amount of excess sludge that is produced van Lier ct al (2008)

summarized the reasons for selecting an anacrobic wastewater treatment process,

identifying sinking advantages of the anaerobic wastewater treatimenL process over

the conventional aerobic treatment processes (Table 1.6) [

Table 1.6 Benefits of the anaerobic treatment process

High applicable COD loading rates reaching 20-35 kg COD-m®*-day", requiring

stnaller reactor volumes

No use of fossil fuels for treatment, saving about 1 kWh-kgCOD" removed,

depending on aeration efficiency

Production of about 15.5 MT CH, energy'kg-COD" removed, giving 1.4 kWh

eleotrieity (asstuning 40% electric conversation cfficicney)

Rapid start-up (< 1 week) using anaerobic granular sludge as seed material

No or vary little use of chemicals

Plain technology with high treatment efficiencies

Anaerobic sludge can be stored unfed, and reactors can be operated during

agricultural campaigns only

Excess sludge has a market value (sold as granular sludge)

High rate system facilitates water recycling in factories (towards closed loops)

The degradation of biological organic compounds under anaerobic conditions is a multistep process involving series and parallel reactions This process of anaerobic degradation proceeds in three stages (’igure 1.12)

1" step: Liydrolyze complex organic compounds into dissolved and low-molccular-weight organic compounds

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2" step: Ferment low-molecular-weight arganic compounds and produce VFAs and alcohols

3" step: Produce methane gas from acetate or hydrogen and carbon dioxide

Figure 1.12 Anaerobic digestion scheme of organic compounds

In general, the 1" step of anaerobic digestion (acidification) is slower than the 2% slep (methane [ermentation) If wastewater contained nonbiedegradable compounds

such as cellos, acidification would be rate-limiting On the other hand, if wastewater

contains easily biodegradable organic compounds, VFAs are rapidly produced and accumulate in the reactor These produced VFAs inhibit methanogens Therefore, consideration of the methane production rate and OLR is important for achieving stable and high process performance in anaerobic wastewater treatment processes

‘The important factors for the anaerobic wastewater treatment process are listed

below

1) The optimal temperature for anacrobie wastewaler treatment processes has been reported to he 30°C ~ 35°C (mesophilic) and SO°C ~ 60°C (thermophilic) A thermophilic anaerobic wastewater treatment process is 25-50% faster than a

mesophilic anaerobic wastewater treatment process

2) The optimal pH ranges for acetogens and methanogens are 5.0 ~ 6.0 and 68 ~ 7.2, respectively Methanogens are more sensitive to pH (less than 6 or higher than 8.0), and the avtivilies of methanogens arc significantly decreased oulside their prefered pH range Tn the anaerobic waslewater treatment process, VFAs are produced as an intermediate and reduce the pH Therefore, alkaline supplementation

is required

3) Nutrients such as phosphorus and nitrogen are required for the growth of

25

anaerobic microorganisms The ratios of COD:N‘P at a high OLR (08 ~ 1.2

kg-COD-kg- VSS -đay”) and low OLK (0.5 kg-COD-kg-VSS”- day”) are 350:7:1

and 1000:7:1, respectively In addition, the optimal N/P and C/N ratios are 7 and at least 25, respectively

4) VFAs and ammonia are known inhibitors of anaerobic digestion VFAs such as

acetale, propionale, and laclic acid are intermediales of anaerobic digestion The

inhibition of methanogens can accur when around 2,500 mg-COD-T.! acetale

accumulates in the reactor at pI 7.5 On the other hand, ammonia inhibition occurs

at 3,500 mg-N-L* under mesophilic conditions and at 2,000 mg-N-L7 under

andusiries involving sugar, potala, slarch, yeast, pectin, cilne acid, canneries,

confectionary, (ruils, vegetables, dairy, and bakeries because of the high biodegradability of the materials (Table 1.7)

One of the main advantages of the anaerobic wastewater treatment process for

industrial wastewater treatment is that it can operate at a high OLR A UASB

reactor is the best technology for high OLR wastewater treatment and is the most widely implemented for anaerobic industrial wastewater, representing about 90% of the market share of all installed systems [32] Tn addition, anaerobic wastewater

treatment cant treal chemical waslewaler containing toxic compounds or wastewater

with a complex composition

26

Table 1.7 Application of anaerobic technology ta industrial wastewater [33]

Tasted

‘Agoroo idly ‘Saga, polats, shach, yeas, pec, aie wal, a0 ty! z3afediotsy, 6 Borage Bea, urdhay, tol diiks, wane, fu neces, celles ” Atratal dinillapy êm jn, cane mi tren, hen mu 1s, grape wine, grin fruit 10 Pulp oncpaperinduatry — Renpels papee,muechamtzel pap, NSEC, alphite poly straw, hogasns 1 Misceltaneons Crical, pharuacentical, suds? igor, lad tH ezchae, acid mine water, min-capal sewage 1

and degrade them into water and carbon dioxide to obtain energy for maintenance

and reproduction The oxidation of organic compounds and the composition of

bacteria cells are shawn in the following reaction equations:

Oxidation of organic compounds

Oxidation of glucose

GgHaO¿ + 602 > 6CO, + OHO + 3.7 keal-gt ————— (1-2

Composilion of bacteria cell

ClHnOm | N | P| O 1E- CO, 1 H;O # Bacteria cell

8(CH,O) | 30, | NH; > CsH,NO, (as bacteria cell) 1 3COQ, 1 6H,0 - (1-3)

Absarb to bacterial or floc

lOxidize by bacteria — HO CO, + Energy

|Capase to bacteria cell