Nghiên cứu công nghệ thích hợp xử lý nước thải quá trình chế biến cao su thiên nhiên

TABLE LISTTable 1 1 Characteristics of natural rubber processing wastewater in Vietnam 11 Table 1 2 National technical regulation on the effluent of natural rubber processing industry in

MINISTRY OF EDUCATION AND TRAINING

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

DEVELOPMENT OF AN APPROPRIATE TREATMENT SYSTEM

FOR NATURAL RUBBER PROCESSING WASTEWATER TREATMENT

CHEMICAL ENGINEERING DISSERTATION

Hanoi – 2022

MINISTRY OF EDUCATION AND TRAINING

HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY

DEVELOPMENT OF AN APPROPRIATE TREATMENT SYSTEM

FOR NATURAL RUBBER PROCESSING WASTEWATER TREATMENT

Major: CHEMICAL ENGINEERING

Code No : NCS16091

CHEMICAL ENGINEERING DISSERTATION

SUPERVISORS:

Hanoi – 2022

Firstly, I would like to thank the Professors and Staff in the Ph D program,

the officers in the Department of Education, Hanoi University of Science and

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

while I have 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

constant encouragement

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

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

which really helps me to become a better person Thank you! You are the best

supervisor ever

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

readers in order to make my Ph D dissertation better

Hanoi, …/…/…

Author of the dissertation

i

I hereby certify that the dissertation "Development of an appropriate

treatment for industrial rubber industrial wastewater treatment" is my own

research project The data and results stated in the doctoral dissertation are honest

I hereby declare that the information cited in the doctoral dissertation has

been fully originated /

Hanoi,…/…/…

ON BEHALF OF SUPERVISORS

Assoc Prof

Author

ACKNOWLEDGMENT i

DECLARATION ii

CONTENTS iii

FIGURE LIST iv

TABLE LIST vi

Introduction 1

Objective 2

Tasks (Scientific and practical meanings) 2

Current Problem and its solution 3

1 State of the art 4

1 1 Natural rubber 4

1 1 1 Natural rubber processing process 7

1 1 2 Natural rubber processing wastewater 9

1 2 Current treatment technology for natural rubber processing wastewater 12

1 2 1 Biological aerobic and anaerobic pond 13

1 2 2 Upflow anaerobic sludge blanket reactor 14

1 2 3 Anaerobic baffled reactor 17

1 2 4 Activated sludge process 19

1 2 5 Swim bed tank 20

1 2 6 Down flow hanging sponge reactor 20

1 2 7 Dissolved air floatation 22

1 2 8 Membrane bioreactor 22

1 2 9 Combination of treatment systems for natural rubber processing wastewater 22

1 3 Industrial wastewater treatment process 23

1 3 1 Characteristics of anaerobic wastewater treatment and the degradation pathway of anaerobic digestion 23

1 3 2 Anaerobic industrial wastewater treatment technology 26

1 3 3 Characteristics of aerobic wastewater treatment and the degradation 27

1 4 Greenhouse gas emissions from the wastewater treatment system 28

2 Material and methods 30

2 1 Filed survey 30

2 1 1 Greenhouse gases collection and analysis 30

2 2 Laboratory UASB-DHS system 32

2 2 1 Raw wastewater 32

2 2 2 System description and operational conditions 34

2 3 Laboratory scale ABR system 35

2 3 1 Raw natural rubber processing wastewater 35

2 3 2 System description and operational conditions 36

2 4 Pilot UASB-DHS system 37

2 5 Analysis 39

2 5 1 Potential of hydrogen 39

2 5 2 Dissolved oxygen 39

2 5 3 Oxidation-reduction potential 39

2 5 4 Chemical oxygen demand 40

2 5 5 Biochemical oxygen demand 40

2 5 6 Suspended solid 41

2 5 7 Total nitrogen 41

2 5 8 Ammonia, nitrite, and nitrate 41

2 5 9 Volatile fatty acid 42

2 5 10 Biogas production and composition 42

3 Results and Discussions 43

3 1 Characterization of a current wastewater treatment system 43

3 2 Development concept of a laboratory scale UASB-DHS system for natural rubber processing wastewater treatment 51

3 3 Development concept of a laboratory scale ABR experiment 58

3 3 1 Process performance of ABR 58

3 3 2 Determinates profiles inside the ABR 60

3 4 Development concept of a pilot scale UASB-DHS system experiment for

treatment of natural rubber processing wastewater 61

3 4 1 Process performance 61

3 4 2 Nitrogen removal and greenhouse gas emissions 67

3 4 3 Performance comparison of ABR-UASB-DHS system and existing treatment system 71

3 5 Design for full-scale UASB-DHS system for natural rubber processing wastewater in Vietnam 75

3 5 1 Reactor design for natural rubber processing wastewater 75

3 5 1 1 Pre-treatment process for UASB reactor 75

3 5 1 2 UASB reactor 77

3 5 1 3 DHS reactor 78

3 5 2 Calculation of Energy consumption and generation for the operation of the UASB-DHS system 78

3 5 2 1 Energy consumption of UASB-DHS system 78

3 5 2 2 Energy production of UASB-DHS system 79

4 Conclusions 80

Recommendation for future study 82

PUBLICATION LIST 83

References 91

FIGURE LIST

Figure 1 1 Top natural rubber produced countries over the world in 2014 [3] 5

Figure 1 2 Natural rubber harvested area and production in Vietnam [2] 6

Figure 1 3 Natural rubber production area in Vietnam [2] 6

Figure 1 4 Natural rubber manufacturing process [5] 8

Figure 1 5 Schematic diagram of coagulation process [5] 9

Figure 1 6 Full-scale biological pond in Vietnam 14

Figure 1 7 Schematic diagram of UASB reactor 16

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 DHS in India 21

Figure 1 11 Development history from DHS G1 to DHS G6 [30] 21

Figure 1 12 Anaerobic digestion scheme of organic compounds 25

Figure 1 13 Aerobic biological degradation pathway 28

Figure 2 1 Schematic diagram of open-type anaerobic system 30

Figure 2 2 Gas sampling system used in this study 32

Figure 2 3 (A) Thanh Hoa Rubber Factory, (B) Coagulation process in natural rubber sheet producing process 33

Figure 2 4 Schematic diagram of the baffled reactor (BR), upflow anaerobic sludge blanket (UASB), and downflow hanging sponge (DHS) combined 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 column, (14) water bath, (15) desulfurizer, (16) gas meter, (17) distributor 35

Figure 2 5 Protocol for preparation of natural rubber processing wastewater

following actual factory methods 36

Figure 2 6 Schematic diagram of anaerobic baffled reactor 36

Figure 2 7 Schematic and photo of the pilot scale ABR-UASB-ST-DHS system 38

Figure 3 1 Biogas composition of compartments 28, 33, and 56 48

Figure 3 2 Methane gas emission rate and COD concentration of each compartment

49

Figure 3 3 COD mass balance in the OAS 49

Figure 3 4 Nitrous oxide rate and ammonia concentration in each compartment 50

Figure 3 5 Composition of emitted GHGs from near the influent part, the center part,

and the effluent part of the OAS 50

Figure 3 6 Time course of pH and temperature during the operation periods 54

Figure 3 7 Time course of (a) total COD, (b) soluble COD, (c) TSS, (d) VSS, and

(e) TN during the operation periods 56

Figure 3 8 COD mass balance of the influent, BR effluent, and UASB effluent

during phase 2 56

Figure 3 9 Time course of (A) Total COD and (B) TSS concentrations through

phase 1 to phase 3 59

Figure 3 10 Soluble COD, acetate, and propionate concentrations in ABR on (A)

103 day and (B) 199 day 61

Figure 3 11 Accumulation of rubber particular in feed pipe and photo of

wastewaters 64

Figure 3 12 Time course of (A) Total COD removal efficiency and organic loading

rate of UASB reactor, (B) Total BOD removal efficiency 66

Figure 3 13 (A) Total nitrogen and (B) ammonia removal efficiency of the total

system and DHS reactor during phase 1 to phase 4 70

References 91

TABLE LIST

Table 1 1 Characteristics of natural rubber processing wastewater in Vietnam 11

Table 1 2 National technical regulation on the effluent of natural rubber processing industry in Vietnam 12

Table 1 3 Type of treatment process applied in Vietnam [4] 13

Table 1 4 Application of UASB reactor for natural rubber processing wastewater treatment 16

Table 1 5 Comparison of technologies used for natural rubber processing wastewater treatment 23

Table 1 6 Benefits of the anaerobic treatment process 24

Table 1 7 Application of anaerobic technology to industrial wastewater [33] 27

Table 1 8 Global warming potential of GHG 29

Table 2 1 Water quality of natural rubber processing wastewater obtained from a natural rubber sheet producing factory in Thanh Hoa Province 33

Table 2 2 Summary of the initial operational conditions for the two operating phases 34

Table 2 3 Operational conditions for anaerobic baffled reactor 37

Table 2 4 Initial operational conditions through phases 1 to 4 39

Table 3 1 Present treatment system flow of a local natural rubber processing factory 44

Table 3 2 Water quality in each sampling point at a local natural rubber processing wastewater in Vietnam 45

Table 3 3 Summary of process performance of the treatment system 57

Table 3 4 Summary of the process parameters of the system during entire experimental period 65

Table 3 5 Biogas production and compositions of the UASB reactor 66Table 3 6 Nitrogen concentrations (mg-N·L-1) in the proposed system 69

Table 3 7 Characteristics of natural rubber processing wastewater in Thailand,

Malaysia, and Vietnam 71

Table 3 8 Process performance of the existing treatment system for treating

natural rubber processing wastewater 74

Table 3 9 Water quality of natural rubber processing wastewater for simulation 75

Abbreviations words list

Chemical oxygen demandDissolved air flotationDownflow hanging spongeDissolved oxygen

Gas chromatographGreenhouse gasGranular-bed anaerobic baffled reactorGas-liquid-solids separation

Global warming potentialHydraulic retention timesMembrane bioreactorOpen-type anaerobic systemOrganic loading rate

Oxidation-reduction potentialPotential of hydrogen

Polyvinyl chlorideRibbed smoked sheetSulfate-reducing bacteriaSettling tank

Standard Vietnamese RubberTotal nitrogen

Technically specified rubberTotal suspended solidsUpflow anaerobic sludge blanketVolatile fatty acids

Volatile suspended solids

Natural rubber is one of the most valuable agricultural products in

Southeast Asian countries Vietnam is the 3rd largest natural rubber-producingcountry, and natural rubber production in Vietnam is increasing each year However,the natural rubber industry discharges large amounts of wastewater containing highconcentrations of organic compounds, nitrogen, and other contaminants from

several manufacturing processes such as coagulation, centrifugation, lamination,washing, and drying The natural rubber processing factories in Southeast Asiancountries commonly use a combined anaerobic-aerobic lagoon system for treatingnatural rubber processing wastewater because of the low installation costs Theexisting treatment systems have been demonstrated to achieve a high chemicaloxygen demand (COD) removal efficiency of 65 to 90% with easy operationalmethods However, they require a large area for the lagoon, high operating costs(especially for surface aeration), and long hydraulic retention times (HRTs)

However, the effluent water quality of these existing treatment systems needs to beimproved to conform to the established discharge standards

An upflow anaerobic sludge blanket (UASB) reactor is one of the mostpromising systems for the treatment of different types of industrial wastewaterbecause of its high organic loading rate (OLR), low operational costs, and energyrecovery in the form of methane Previous studies have reported the application ofthe 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 Therefore, thedevelopment of a pre-treatment system to remove the remaining natural rubberparticles is essential Moreover, when a UASB reactor is used to treat high-strengthindustrial wastewater, the effluent still contains high concentrations of organiccompounds and nutrients Thus, an aerobic treatment system is typically applied as

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

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

different types of industrial wastewater

Objective

Current wastewater treatment systems used to treat natural rubber

processing wastewater in Vietnam consume a large amount of electrical energy andhave a large negative impact on the environment In this study, we characterized theprocess performance (e g , water quality and biogas emission) of the current

wastewater treatment system and developed an energy-recovery type advancedwastewater treatment system to reduce greenhouse gas (GHG) emissions and

improve the effluent quality resulting from the treatment of natural rubber

processing wastewater

Tasks (Scientific and practical meanings)

1) Characterization of the current wastewater treatment system used to treat naturalrubber processing wastewater in Vietnam

To investigate the current situation of natural rubber processing

wastewater treatment in Vietnam, field, and journal paper surveys were conducted Moreover, GHG emissions from an existing anaerobic lagoon were measured todetermine the environmental impact on global warming

2) Development of an energy-recovery type wastewater treatment system

The UASB-DHS system has been applied to treat domestic sewage andseveral types of wastewater In addition, the UASB-DHS system was successfullyapplied in Thailand to treat natural rubber processing wastewater, which contained ahigh concentration of sulfuric acid In this study, we examined the application of theUASB-DHS system for treating natural rubber processing wastewater in Vietnamand evaluated its process performance at the laboratory scale and in a pilot-scaleexperiment

3) Establishment of an optimal treatment system for natural rubber processingwastewater treatment in Vietnam

Following these results, we established an optimal treatment system fornatural rubber processing wastewater treatment in Vietnam

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

we developed is known to be an energy-recovery and energy-saving wastewatertreatment system and has been applied to several types of wastewater If the

application of the UASB-DHS system to natural rubber processing wastewater inVietnam is successful, it could reduce operational costs and GHG emissions andimprove the effluent quality Moreover, this advanced wastewater treatment

technology can be applied to not only natural rubber processing wastewater but alsoother industrial wastewater emitted in Vietnam

Current Problem and its solution

· The discharge amount of industrial wastewater in Vietnam is expected to increaseeach year

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

of this type of system is very expensive

· The UASB-DHS system we developed is known to be an energy-recovery andenergy-saving wastewater treatment system and has been applied to several types ofwastewater

· If the application of the UASB-DHS system to natural rubber processing

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

wastewater but also other industrial wastewater emitted in Vietnam

1 State of the art

1 1 Natural rubber

Rubber is widely used in industry and can be categorized as natural rubber andsynthetic rubber Natural rubber consists of polymers of the organic compoundisoprene, with minor impurities consisting of other organic compounds and water The natural rubber has good wear resistance and high elasticity, resilience, andtensile strength It has a good dynamic performance and a low level of damping Therefore, 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 from coal oil Synthetic rubbers are more resistant tooil, certain chemicals, and oxygen and have better aging and weathering

characteristics and good resilience over a wider temperature range Both naturalrubber and synthetic rubber can be used properly according to the application, butthey are combined like an automobile tires The total amount of rubber consumed in

2017 reached 28,287,000 tons, and this was a 3% increase compared with the

amount consumed in 2016 over the world In 2017, the amount of natural rubberproduced increased to 13,380,000 tons Thailand and Indonesia produce over 60%

of the total amount of natural rubber (Figure 1 1)

Vietnam is the 3rd largest natural rubber producer in the world and produced1,094,500 tons in 2017 [2] The quality of the natural rubber produced and theharvested area in Vietnam have increased each year (Figure 1 2) The rubber tree isgrown mostly in the Binh Phuoc, Binh Duong, Tay Ninh, and Dong Nai provinces

in the Southeast region of Vietnam because of their favorable climate and suitableland for the optimal growth of rubber trees (Figure 1 3) The optimal growth

conditions for rubber trees are as follows:

· Rainfall of around 250 cm 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 strong winds

Top 10 of Natural Rubber Processing Countries (2014)

Philippines Guatemala Côte d'Ivoire Myanmar Others

Figure 1 1 Top natural rubber produced countries over the world in 2014 [3]

Figure 1 2 Natural rubber harvested area and production in Vietnam [2]

Figure 1 3 Natural rubber production area in Vietnam [2]

1 1 1 Natural rubber processing process

Natural rubber is harvested mainly in form of the latex from the rubber tree (Hevea

brasiliensis) or other trees Figure 1 4 show the production process for rubber

products in a natural rubber processing factory [4][5] Latex is a sticky, milkycolloid that is obtained by making an incision in the bark and collecting the fluid invessels in a process called “tapping ” Raw natural rubber latex is collected from arubber tree, and ammonia is immediately added to keep it at a high pH to preventcoagulation Anti-coagulation measures are especially necessary under wet weatherconditions and with lattices that have a strong tendency for pre-coagulation

Therefore, the amount of anti-coagulant used during the wet season is higher thanthat used in the dry season Nguyen (1999) noted that the amount of ammonia thatshould be added to latex to prevent natural coagulation depends on the season [6]

· Wet season: 1 0 – 2 0 kg·tons dry rubber-1 (0 1 – 0 2% wet weight)

· Dry season: 0 5-1 5 kg·tons dry rubber-1 (0 05 – 0 15% wet weight)

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

After it is transferred to the factory, natural rubber latex is first filtered through amesh screen to removed collated rubber, particles, leaves, and other material Then

it is diluted with tap water Acids such as acetate or formic acid are added to

coagulate it into 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

The products of natural rubber latex are manufactured in a local factory into threetypes of raw rubber sheets: technically specified rubber (TSR), concentrated latex(CL), and ribbed smoked sheet (RSS) TSR is graded in a quality inspection after it

is formed TSR is also called “blocked rubber” or “crumb rubber” because of its

morphology TSR is the most widely used type in the US and European countries

RSS is a smoked rubber sheet and is largely used in industry

Figure 1 4 Natural rubber manufacturing process [5]

8

Diluted

Acetic/formic acid Coagulated

Acid

Serum (Wastewater)

Figure 1 5 Schematic diagram of coagulation process [5]

1 1 2 Natural rubber processing wastewater

The main products from local natural rubber processing factories are CLand RSS The production processes for these products such as coagulation,

centrifugation, lamination, washing, and drying use a large amount of fresh waterand discharge the same amount of wastewater In Vietnam, surface water andgroundwater are mostly used A previous study reported that in Vietnam 25 m3 ofwastewater is discharged from the production of 1 ton of RSS from fresh latex,whereas approximately 18 m3 of wastewater is discharged to produce 1 ton of CL[7] This wastewater is heavily polluted, and it is causing environmental problemsbecause of insufficient wastewater treatment [8] The characteristics of naturalrubber processing wastewater are very different between the RSS and latexproduction processes Table 1 1 summarizes the effluent quality of natural rubberprocessing wastewater in Vietnam Nguyen (2003) surveyed 27 rubber processingfactories in five provinces and summarized the quality of their effluents [4] Thesewastewaters mainly contained wash water and small amounts of uncoagulated latexand serum with small quantities of proteins, carbohydrates, lipids, carotenoids, andsalts The wastewater discharged from the CL producing process is the mostpolluted wastewater compared to other wastewater because this wastewater containshigh concentrations of uncoagulated rubber particles and organic matter [7] The

9

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

20,000 mg·L-1 and 500 mg·L-1, respectively The wastewater discharged from

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

pH 4 8~5 5) The main organic compounds in this natural rubber processing

wastewater are volatile fatty acids (VFAs) Acetate and formic acid have beenwidely used for field latex coagulation in Vietnam Specifically, the natural rubberprocessing wastewater collected from the coagulation process at a rubber processingfactory in Thanh Hoa province, Vietnam, was reported to contain 4,000

mg-COD·L-1 acetate and 4,500 mg-COD·L-1 propionate [9]

Both CL wastewater and SVR wastewater contain a high concentration ofammonia (e g , 100 mg-N·L-1 to 1,000 mg-N·L-1) Ammonia is added to the latex inthe tapping cups and collecting buckets to increase the pH of the latex to preventpremature coagulation The amount of ammonia added to latex to prevent naturalcoagulation depends on the season and the distance from the collection site to theprocessing factory [10] The wastewater from CL factories contains a high

concentration of nitrogen

The industrial effluent discharge standards for environmental protectionare usually provided by the government Natural rubber processing wastewater isone of the largest sources of industrial wastewater pollution in Southeast Asiancountries, and usually, specific and strict effluent standards are established fornatural rubber processing factories In Vietnam, the Ministry of Natural Resourcesand the Environment provides national technical regulations for the effluent of thenatural rubber processing industry (QCVN 01-MT: 2015/BTNMT) The Vietnameseeffluent standards for water quality are shown in Table 1 2 Standard A is applied foreffluent discharged into the domestic water supply (used for daily activities, exceptdirectly for drinking and cooking) Standard B is applied for other water suppliesother than the domestic water supply (e g , water transport, irrigation, aquaculture,cultivation) The national technical regulations published in 2015 contain two

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

factories (started operation before 31/March/2015)

Table 1 1 Characteristics of natural rubber processing wastewater in Vietnam

Factory

Type of product

Parameter Unit

Crumb from latex

Crumb from lower Sheets grade

Latex concentrate

Thanh Hoa SVR

Binh Duong SVR

5 9 2,720 1,594 48 - 40 67

5 1 4,350 2,514 150 - 110 80

4 8 6,212 4,010 565 - 426 122

23,200 12,000 - - - 1,450

-5 -5 3,860 3,560 - 273 171 240 Reference Nguyen (2003) Watari et al (2015) Watari et al (2017)

Parameter Loc Hiep Quan Loi Tan Lap Tan Bien Ven Ven Bo La Xuan Lap Type of product

Contenctrate

d latex + SVR

Cocentrate Cocentra

d latax ted latax

Contenctrat Contenctrate

ed latex + d latex + SVR SVR

Cocentrated Contenctrated latex + latex SVR

mg· L -1

10,780 18,885 - 611 341 900

26,914 8,750 - 766 361 740

19,029 7,830 - 713 302 713

14,466 9,200 - 450 350 850

26,436 13,820 - 651 285 1,690

13,981 7,590 - 972 686 468

11,935 8,780 - 1,306 1,043 1,164 Reference

SVR: Standard Vietnam Rubber

Nguyen and Luong (2012)

Table 1 2 National technical regulation on the effluent of natural rubber processing

industry in Vietnam (QCVN 01-MT: 2015/BTNMT)

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

system needs to remove these rubber particulates Currently, several types of

wastewater treatment 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 The effluent treatment processes in use in Vietnam

were surveyed by Nguyen (2003) [4] Aerated lagoons and ponds are commonly

used for the treatment of this wastewater On the other hand, the application of

advanced treatment processes such as dissolved air flotation (DAF) and a UASB

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

pond method have been widely applied

Table 1 3 Type of treatment process applied in Vietnam [4]

Type of treatment process

Aerated lagoon

Pond

Dissolved air flotation

Upflow anaerobic sludge blanket

1 2 1 Biological aerobic and anaerobic pond

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

of natural rubber processing wastewater in Southeast Asian countries (Figure 1 6) More than 500 anaerobic biological ponds have been installed in Malaysia for palmoil and natural rubber processing factories [11][12][8][13] With this system, it ispossible to achieve a high organic removal efficiency with low operational andinstallation costs The oxidation ditch process (aerated lagoon) is the most populartreatment system for natural rubber processing wastewater in Vietnam [4] In thissystem, usually, 2, 4, or 6 units are arranged in series, parallel, or both and equippedwith surface floating type aerators Ibrahim (1980) demonstrated the possibility ofachieving efficient ammonia nitrogen removal in a laboratory-scale experiment [14] Currently, this process is combined with a rubber trap and/or anaerobic lagoon, andthe 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 naturalrubber production [15] In addition, GHG emissions from the oxidation ditch

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

A UASB reactor is one of the most promising systems for the treatment ofdifferent types of industrial wastewater because of its high OLR capacity, lowoperational costs, and energy recovery in the form of methane [16] The formation

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

successful UASB reactor (Figure 1 7) The characteristics of the UASB are listedbelow

1)

2)

The influent is fed from a bottom reactor to create upflow

If the UASB reactor is correctly operated, granulation can occur and result

in the formation of high settleability sludge in the reactor

3) The UASB reactor has high contacting efficiency because of high biogasproduction

4)

5)

The washed-out sludge is effectively collected by the GSS

There is 90% less excess sludge from the UASB reactor compared withthat from an activated sludge process

Table 1 4 summarizes the process performance of the UASB reactor whentreating natural rubber processing wastewater The first application of a UASBreactor 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-3·day-1 However, the remaining natural rubber particulates, such asaccumulated rubber particulates in the UASB column, affected the anaerobic

biodegradation Therefore, an effective pre-treatment process to remove residualnatural rubber particulates is required for the application of UASB reactors in

Vietnamese local natural rubber processing factories Nguyen et al (2016) reportedthat the granulation was enhanced with the use of aluminum chloride, and the totalCOD removal efficiency of the UASB reactor increased to 96 5 ± 2 6%, with amethane recovery rate of 84 9 ± 13 4%, for natural rubber processing wastewater inVietnam [17]

The UASB technology for natural rubber 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 atwo-stage UASB reactor applied to CL processing wastewater [10] The resultsindicated that the UASB reactor achieved a high process performance when the pHwas controlled at 7 and operated under mesophilic conditions (35°C) on a

laboratory-scale level Tanikawa et al (2016) examined a pilot-scale two-stageUASB reactor (volumes of 997 L and 597 L, respectively) in the Von Bundit naturalrubber processing factory in Sra Thani, Thailand [18] The system achieved a CODremoval efficiency of 95 7% ± 1 3% at an OLR of 0 8 kgCOD·m-3·d-1 Bacterialactivity measurement in the retained sludge from the UASB revealed high activity

of sulfate-reducing bacteria (SRB), especially hydrogen-utilizing SRB, comparedwith that of methane-producing bacteria

1 2 3 Anaerobic baffled reactor

An aerobic baffled reactor (ABR) has been designed since the early 1980s and hasseveral advantages over a well-established system such as a UASB reactor andanaerobic filter [16] These advantages are better resilience to hydraulic and organicshock loadings, longer biomass retention times, lower sludge yields, and the ability

to partially separate the various phases of anaerobic catabolism The most

significant advantage of the ABR is the typical reactor configuration that can

separate acetogen and methanogen longitudinally down the reactor This two phasesoperation can enhance acetogen and methanogen activity by a factor of up to four asacetogen accumulates within the first stage, and the different microbial groups candevelop under more favorable conditions Therefore, the ABR has been applied tothe treatment of various industrial wastewater summarized advantages associatedwith the ABR are shown below:

Constriction

1) Simple design; 2) No moving part; 3) No mechanical mixing; 4) Inexpensiveconstriction; 5) High void volume; 6) Reduced clogging; 7) Reduced sludge bedexpansion;

Biomass

1) No requirement for biomass with unusual settling properties; 2) Low sludgegeneration; 3) High solids retention time; 4) Retention of biomass with fixedmedia or solid-settling chamber; 5) No special gas or sludge separation requiredOperation

1) Low HRT; 2) Intermittent operation possible; 3) Extremely stable to hydraulicshock loads; 4) Protection from toxic materials in influent; 5) Long operationtimes without sludge wasting; 6) High stability to organic shock

Figure 1 8 shows various reactor configurations of ABR Since ABR was proposed,several types of reactor configurations were designed The first report of ABR wasequipped 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-3·day-1 [16] Figure 1 8 (A) is a basic design of ABRthat is vertically separated by the wall Figure 1 8 (B) installed a chamber for

settling and a gas sampling line in each compartment for improvement of retentiontime of waste solid In Figure 1 8 (C), the diameter of the downflow compartmentmade narrow, the increased sludge retention time in the up-flow compartment

Akunna and Clark (2000) reported the performance of a granular-bedanaerobic baffled reactor (GRABBA) applied in the treatment of whisky distillerywastewater [17] The GRABBA used granular sludge for inoculation and it can becompatible with both advantages of the UASB reactor and ABR

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 industrialwastewater treatment worldwide There is a large variety of designs; however, inprinciple, all activated sludge processes consist of three main components: anaeration tank, which serves as a bioreactor; a settling tank (“final clarifier”) for theseparation of solids and treated wastewater in the activated sludge; and a returnactivated sludge apparatus to transfer the settled activated sludge from the clarifier

to the influent of the aeration tank (Figure 1 9) Atmospheric air is introduced into amixture of primary treated or screened sewage combined with organisms to develop

a biological floc This aeration process requires a huge amount of electricity Theaeration tank retains the floc that contains 2,000 ~ 5,000 mg·L-1 bacteria The main

bacterial groups in the aeration tank are the phyla Pseudomonas, Bacillus,

Microbacterium, Acinetobacter, and Nocardia In addition, Protozoa and Metazoa

grow in the aeration tank, resulting in high microbial diversity in this ecosystemwith 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 and middle-strength industrial wastewater Nguyen (2002) reported that the

low-activated sludge process can achieve removal efficiencies of 52% for COD and 25%for Total Kjeldahl Nitrogen in natural rubber processing wastewater treatment with

an OLR of 4 0 kg ·m-3·day-1 [4]

Figure 1 9 Basic water flow in conventional activated sludge

1 2 5 Swim bed tank

The swim-bed technology, involving a novel acryl-fiber biomass

carrier-biofringe, is a new approach for wastewater treatment, especially for thehigh-rate treatment of organic wastewater Nguyen et al (2012) examined a

laboratory-scale swim-bed technology for latex wastewater and found good organicremoval and nitrification at an OLR of 1 0 kg ·m-3·day-1 [4]

1 2 6 Down flow hanging sponge reactor

A DHS reactor is a trickling filter that uses a sponge as the medium(Figure 1 10) In 1997, the group of Prof Harada and collaborators first developed asponge-based bioreactor, as a novel cost-effective post-treatment method for

anaerobically pre-treated sewage [18] Many research papers on the performance ofDHS reactors for treating sewage have been published [19-27] To date, six types ofsponge carriers have been proposed and their process performance demonstrated[19] The most promising post-treatment system is a conventional aerated tankbecause an aerated tank has the ability to provide a high effluent quality with

superior organic and nitrogen removal efficiencies However, the process requires alarge amount of electricity for oxygen supplementation and produces large amounts

of excess sludge Algal tanks have also been applied to treat effluent from theanaerobic tank treatment of natural rubber processing wastewater [20] This systemefficiently removes organics and nitrogen, but it requires a long HRT and a largetreatment area, as do conventional aerated tanks

Figure 1 11 presents a summary of the sixth sponge carriers developed forDHS reactors Currently, the G-3 type sponge is widely used because of its highprocess performance The highlight of the DHS reactor is that it can be operatedwithout aeration or with low aeration requirements, as oxygen is naturally dissolved

in wastewater In addition, the sponge media support a large amount of biomass aswell as high microbial diversity on the surface and in the inner section of the spongemedia The high microbial diversity in this ecosystem with an extremely long foodchain reduces the production of excess sludge [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 applied for the treatment of several types ofindustrial wastewater, especially the post-treatment of UASB reactor-treatedhigh-strength industrial wastewater [23][24] Several studies have reported thetreatment of molasses wastewater using a UASB-DHS system [34-36] Moreover,the DHS reactor has been applied to treat reactive dye wastewater [26], freshwateraquariums [27] [28], and ethylene glycol-containing industrial wastewater [29]

Figure 1 10 Principle of downflow

hanging sponge reactor and full-scale DHS in India

Figure 1 11 Development history from DHS G1 to DHS G6 [30]

1 2 7 Dissolved air floatation

The DAF process clarifies wastewaters 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 withlow turbidity and high color for drinking water treatment In natural rubber

processing wastewater treatment, the DAF process can achieve a high removalefficiency of suspended solids, but the high cost of this process prevents its wideapplication [7]

1 2 8 Membrane bioreactor

A membrane bioreactor (MBR) combines a membrane process such asmicrofiltration or ultrafiltration and a biological wastewater treatment process such

as an activated sludge process The application of an MBR for natural rubber

processing wastewater has been demonstrated by Sulaimanal et al (2010) [31] TheMBR system at a flux of 0 009 m3·m-2·h-1 achieved better removal efficiencies than

an oxidation ditch for all parameters

An anaerobic membrane bioreactor (AnMBR), which combines an

anaerobic process and membrane technology, is considered a very appealing

alternative for wastewater treatment because of its significant advantages overconventional anaerobic treatment AnMBR can achieve a high OLR of 12 7 kg

·m-3·day-1 for latex serum treatment together with methane recovery [31] All MBRapplications for natural rubber processing wastewater have only been demonstrated

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

processing wastewater is expected

1 2 9 Combination of treatment systems for natural rubber processing wastewater

Table 1 5 summarizes the wastewater treatment technologies for naturalrubber processing wastewater Each process has advantages and disadvantages Fornatural rubber processing wastewater treatment, several wastewater treatment

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

in almost all processing factories as a post-treatment to remove the remaining

natural rubber particulates in the wastewater system The combination of an

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

factories have installed a UASB reactor instead of an anaerobic lagoon

Table 1 5 Comparison of technologies used for natural rubber processing

wastewater treatment

Biological anaerobic pond

Oxidation

Activated Swim-bed sludge technology

Low High

High Low

Moderate High

1 0 kg-COD·

m -3 · day -1

Moderate

Low Low

High Low Hydradic

Low Low High

Low Moderate Low

Low Low High

Low Low Moderate

Low Low High

Low Low High Tempurature

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 wastewatertreatment process than aerobic wastewater treatment processes Anaerobic

wastewater treatment can effectively remove biodegradable organic compounds,leaving mineralized compounds such as NH4+ and PO43- in the solution The

bioreactor for an anaerobic wastewater treatment process is a very simple systemand can be applied at any scale and in almost any place The main benefit of theanaerobic wastewater treatment process is that useful energy in the form of methanecan be recovered In general, 40 ~ 45 m3 of biogas can be recovered from 100kg-COD of influent [32] In addition, an anaerobic wastewater treatment processcan reduce the large amount of excess sludge that is produced van Lier et al (2008)summarized the reasons for selecting an anaerobic wastewater treatment process,identifying striking advantages of the anaerobic wastewater treatment process overthe conventional aerobic treatment processes (Table 1 6) [32]

Table 1 6 Benefits of the anaerobic treatment process

· Reduction of excess sludge production up to 90% compared with the aerobic

wastewater treatment process

· Up to 90% reduction in space requirement

· High applicable COD loading rates reaching 20-35 kg COD·m-3·day-1, requiring

smaller reactor volumes

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

depending on aeration efficiency

· Production of about 15 5 MJ CH4 energy·kg-COD-1 removed, giving 1 4 kWhelectricity (assuming 40% electric conversation efficiency)

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

· No or very little use of chemicals

· Plain technology with high treatment efficiencies

· Anaerobic sludge can be stored unfed, 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 (Figure 1 12)

1st step: Hydrolyze complex organic compounds into dissolved andlow-molecular-weight organic compounds

2nd step: Ferment low-molecular-weight organic compounds and produce VFAs and

alcohols

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

Figure 1 12 Anaerobic digestion scheme of organic compounds

In general, the 1st step of anaerobic digestion (acidification) is slower than

the 2nd step (methane fermentation) If wastewater contained nonbiodegradable

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 anaerobic wastewater treatment processes has been

reported to be 30°C ~ 35°C (mesophilic) and 50°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 6 8 ~

7 2, respectively Methanogens are more sensitive to pH (less than 6 or higher than

8 0), and the activities of methanogens are significantly decreased outside their

preferred pH range In the anaerobic wastewater 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

anaerobic microorganisms The ratios of COD:N:P at a high OLR (0 8 ~ 1 2

kg-COD·kg- VSS-1·day-1) and low OLR (0 5 kg-COD·kg-VSS-1·day-1) 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

acetate, propionate, and lactic acid are intermediates of anaerobic digestion The

inhibition of methanogens can occur when around 2,500 mg-COD·L-1 acetate

accumulates in the reactor at pH 7 5 On the other hand, ammonia inhibition occurs

at 3,500 mg-N·L-1 under mesophilic conditions and at 2,000 mg-N·L-1 under

thermophilic conditions

1 3 2 Anaerobic industrial wastewater treatment technology

During the last 40 years, anaerobic wastewater treatment technology has

evolved from localized lab-scale experiments to successful worldwideimplementation in various industries [33] Currently, more than 1,600 real-scale

anaerobic wastewater treatment plants are operating worldwide [44-46] Previous

studies have reported the process performance of anaerobic wastewater treatment

processes for treating many types of medium- and high-strength industrial

wastewater [34] Specifically, these processes are widely applied in some agro-foodindustries involving sugar, potato, starch, yeast, pectin, citric acid, canneries,

confectionary, fruits, 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] In addition, anaerobic wastewater

treatment can treat chemical wastewater containing toxic compounds or wastewater

with a complex composition

Table 1 7 Application of anaerobic technology to industrial wastewater [33]

Installed reactors Industrial sector

Can juice, cane molasses, beet molasses, grape wine, grain fruit Recycle paper, mechanical pulp, NSSC, sulphite pulp, straw, bagasse Chemical, pharmaceutical, sludge liqor, landfill leachate, acid mine water, minicipal sewage

(% of total) 36 29 10 11 14

1 3 3 Characteristics of aerobic wastewater treatment and the

degradation

Aerobic treatment is a removal process in which organic compounds, ammonia,

odors, and iron are oxidized by several types of aerobic bacteria under conditions of

oxygen availability (Figure 1 13) The bacteria or floc absorb organic compounds

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

and reproduction The oxidation of organic compounds and composition of bacteria

cells are shown in the following reaction equations:

Oxidation of organic compounds

ClHnOm + N + P + O +E → CO2 + H2O + Bacteria cell

8(CH2O) + 3O2 + NH3 → C5H7NO2 (as bacteria cell) + 3CO2 + 6H2O - (1-3)

Figure 1 13 Aerobic biological degradation pathway

1 4 Greenhouse gas emissions from the wastewater treatment system

A GHG is a gas that absorbs and emits radiant energy within the thermal

infrared range The primary GHGs in the Earth’s atmosphere are water vapor,

carbon dioxide, methane, nitrous oxide, and ozone Global warming potential

(GWP) is used to compare the amount of heat trapped by a certain mass of the gas

in question to the amount of heat trapped by a similar mass of carbon dioxide (Table

1 8) The GWP depends on the following factors:

· The absorption of infrared radiation by a given species

· The spectral location of its absorbing wavelengths

· The atmospheric lifetime of the species

A wastewater treatment plant also emits a considerable amount of GHG

into the atmosphere Approximately 3 4% of GHGs are emitted from waste disposaland treatment processes Methane is one of the main GHGs emitted from

wastewater treatment processes In addition, nitrous oxide (N2O) can be emitted

during wastewater treatment when WWTPs are operated at a low DO concentration

in the nitrification and denitrification processes and a low COD/N ratio in the

denitrification process [35] The emission of GHGs from sewage treatment plants

has been well studied, but that from the treatment of natural rubber processing

wastewater has not been documented