TÓM TẮT KẾT LUẬN MỚI CỦA LUẬN ÁN Nghiên cứu và thống kê các vấn đề môi trường và hệ thống xử lý hiện tại đối với nước thải chế biến cao su tự nhiên ở Việt Nam. Phát triển hệ thống xử lý mới, tên gọi BRUASBDHS, nhằm xử lý nước thải có ô nhiễm hữu cơ cao và thu hồi năng lượng dưới dạng khí sinh học. Làm sáng tỏ tác động của sự đa dạng thành phần vi sinh vật đối với phương pháp xử lý sinh học, từ đó có các phương án vận hành để tăng hiệu quả loại chất ô nhiễm và khả năng sản xuất khí sinh học.
Trang 1MINISTRY OF EDUCATION AND TRAINING
HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Takahiro Watari
DEVELOPMENT OF AN APPROPRIATE TREATMENT SYSTEM FOR
NATURAL RUBBER INDUSTRIAL WASTEWATER TREATMENT
CHEMICAL ENGINEERING DISSERTATION
Trang 2MINISTRY OF EDUCATION AND TRAINING
HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Takahiro Watari
DEVELOPMENT OF AN APPROPRIATE TREATMENT SYSTEM FOR
NATURAL RUBBER INDUSTRIAL WASTEWATER TREATMENT
Major: CHEMICAL ENGINEERING
Code No.: 9520301
CHEMICAL ENGINEERING DISSERTATION
SUPERVISORS:
1 Assoc Prof Nguyen Minh Tan
2 Prof Takashi Yamaguchi
Trang 3Firstly I would like to thank the teachers in the PhD 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 privilage 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 Nguyen Minh Tan 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 encourgement and full support from the readers in order to make my PhD disertation better
Hanoi, 2.12.2019
Author of the dissertation
Takahiro Watari
Trang 4I 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, 2.12.2019
ON BEHALF OF SUPERVISORS Author
Assoc Prof Nguyen Minh Tan Takahiro Watari
Trang 5
Current Problems and its solution 3
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
13
1.2.1 Biological aerobic and anaerobic pond 14 1.2.2 Upflow anaerobic sludge blanket 15 1.2.3 Anaerobic baffled reactor 18 1.2.4 Activated sludge process 21
1.2.6 Down flow hanging sponge reactor 22 1.2.7 Dissolved air floatation 24
1.4 Greenhouse gas emission from wastewater treatment system 32
2.1.1 Greenhouse gases collection and analysis 34
2.2.2 System description and operational conditions 38 2.3 Laboratory scale ABR system 40 2.3.1 Raw natural rubber processing wastewater 40 2.3.2 System description and operational conditions 40
Trang 62.5.4 Biochemical oxygen demand 45
2.5.7 Ammonia, nitrite and nitrate 46 2.5.8 Volatile fatty acid (VFA) 47 2.5.9 Biogas production and composition 48
3.1 Characterization of current wastewater treatment system 49 3.1.1 Characterization of greenhouse gas emission process from
current anaerobic tank
53
3.2 Development concept of a laboratory scale UASB-DHS system for
natural rubber processing wastewater treatment
58
3.2.1 Process performance of laboratory scale UASB-DHS system 58 3.3 Development concept of a laboratory scale ABR experiment 65 3.3.1 Process performance of ABR 65 3.3.2 Determinates profiles inside the ABR 68 3.4 Development concept of a pilot scale UASB-DHS system
experiment for treatment of natural rubber processing wastewater
3.5 Design guideline for full scale UASB-DHS system for natural
rubber processing wastewater in Vietnam
3.5.2 Calculation of Energy consumption and generation for
operation of UASB-DHS system
Trang 7DHS in India
23
Figure 1.11 Development history from DHS G1 to DHS G6 24 Figure 1.12 Anaerobic digestion scheme of organic compounds 28 Figure 1.13 Aerobic biological degradation pathway 31
Figure 2.1 Schematic diagram of open-type anaerobic system 33 Figure 2.2 Gas sampling system used in this study 35 Figure 2.3 (A) Location of Thanh Hoa province, Vietnam, (B) Thanh
Hoa Rubber Factory, (C) Coagulation process in natural rubber sheet producing process
36
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
39
Figure 2.5 Protocol for preparation of natural rubber processing
wastewater following actual factory methods
Trang 8the center part, and the effluent part of the OAS.
Figure 3.7 Time course of pH and temperature during the operation
periods
60
Figure 3.8 Time course of (a) total COD, (b) soluble COD, (c) TSS, (d)
VSS and (e) TN during the operation periods
62
Figure 3.9 COD mass balance of the influent, BR effluent, and UASB
effluent
64
Figure 3.10 Time course of (A) Total COD and (B) TSS concentrations
through phase 1 to phase 3
67
Figure 3.11 Soluble COD, acetate and propionate concentrations in
ABR on (A) 103 day and (B) 199 day
69
Figure 3.12 Accumulation of rubber particular in feed pipe and photo of
wastewaters
73
Figure 3.13 Time course of (A) Total COD removal efficiency and
organic loading rate of UASB reactor, (B) Total BOD removal efficiency
75
Figure 3.14 (A) Total nitrogen and (B) ammonia removal efficiency of
total system and DHS reactor during phase 1 to phase 4
79
Trang 9Table 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
Table 1.5 Comparison of technologies used for natural rubber
processing wastewater treatment
rubber processing wastewater in Vietnam
Table 3.6 Characteristics of natural rubber processing wastewater in
Thailand, Malaysia and Vietnam
81
Table 3.7 Process performance of the existing treatment system for
treating natural rubber processing wastewater
83
Trang 10Abbreviation words list
ABR anaerobic baffled reactor
AnMBR anaerobic membrane bioreactor
BOD biochemical oxygen demand
BR baffled reactor
CL concentrated latex
COD chemical oxygen demand
DAF dissolved air flotation
DHS downflow hanging sponge
DO dissolved oxygen
GHG greenhouse gas
GRABAA granular-bed anaerobic baffled reactor GSS gas-liquid-solids separation
GWP global warming potential
HRT hydraulic retention time
MBR membrane bioreactor
OAS open-type anaerobic system
OLR organic loading rate
ORP oxidation reduction potential
TSR technically specified rubber
TSS total suspended solids
UASB upflow anaerobic sludge blanket VFA volatile fatty acid
VSS volatile suspended solids
pH potential of hydrogen
Trang 11Introduction
Natural rubber is one of the most valuable agricultural products in Southeast Asian countries Vietnam is the 3rd largest natural rubber-producing country, and natural rubber production in Vietnam is increasing each year However, the natural rubber industry discharges large amounts of wastewater containing high concentrations 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 Asian countries commonly use a combined anaerobic-aerobic lagoon system for treating natural rubber processing wastewater because of the low installation costs The existing treatment systems have been demonstrated to achieve a high chemical oxygen demand (COD) removal efficiency of 65 to 90% with easy operational methods 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 be improved in order 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 its high organic loading rate (OLR), low operational costs, and energy recovery in the form of methane Previous studies have reported the application 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 Therefore, the development of a pre-treatment system to remove the remaining natural rubber particles is essential Moreover, when a UASB reactor is used to treat high-strength industrial wastewater, the effluent still contains high concentrations of organic compounds and nutrients Thus, an aerobic treatment system is typically applied as a post-treatment to remove
Trang 12post-treatment with the UASB reactor to treat different types of industrial
wastewaters
Objective
Current wastewater treatment systems used to treat natural rubber processing wastewater in Vietnam consume a large amount of electrical energy and have a large negative impact on the environment In this study, we characterized the process performance (e.g., water quality and biogas emission) of the current wastewater treatment system and developed an energy-recovery type advanced wastewater treatment system to reduce greenhouse gases (GHGes) emission 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 natural rubber 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, greenhouse gas emissions from an existing anaerobic lagoon were measured to determine the environmental impact on global warming This research will make clear problems in current situation of natural rubber processing wastewater treatment in an actual site Moreover, GHGes emission from current wastewater treatment system firstly investigated
2) Development of an energy-recovery type wastewater treatment 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
Trang 13evaluated its process performance at the laboratory scale and in a pilot-scale experiment This result expected that establishment of next generation wastewater treatment process that can achieve not only wastewater treatment but also energy recovery
3) Establishment of an optimal treatment system for natural rubber processing
wastewater treatment in Vietnam
Following these results, we established an optimal treatment system for natural rubber processing wastewater treatment 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 is very expensive
· The UASB-DHS system we developed is known to be an energy-recovery and energy-saving wastewater treatment system and has been applied to several types of wastewater
· If the application of the UASB-DHS system to natural rubber processing wastewater in Vietnam is successful, it could reduce the operational costs and greenhouse gas emissions and improve the effluent quality Moreover, this advanced wastewater treatment technology can be applied to not only natural rubber processing waste water, but also other industrial wastewaters emitted in Vietnam
Trang 141 State of the art
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 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 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 to oil, certain chemicals, and oxygen and have better aging and weathering characteristics and good resilience over a wider temperature range Both natural rubber and synthetic rubber can be used properly according to the application, but they are combined like an automobile tire 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 (IRSG report) In 2017, the amount of natural rubber produced 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 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 in Vietnam because of their 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 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
Trang 15· 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
Figure 1.1 Top natural rubber produced countries over the world on 2014 [3]
Philippines Guatemala Côte d'Ivoire Myanmar Others
Trang 16Figure 1.2 Natural rubber harvested area and production in Vietnam [2]
800,000 700,000 600,000 500,000 400,000 300,000 200,000 100,000
0 Southern region
Highlands Central region Northern
Trang 171.1.1 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] The latex is a sticky, milky colloid that is obtained by making an incision in the bark and collecting the fluid in vessels in a process called “tapping.” Raw natural rubber latex is collected from a rubber tree, and ammonia is immediately added to keep it at 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 ammonia that should 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 the processing factory
After it is transferred to the factory, natural rubber latex is first filtered through a mesh 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 three types 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
Trang 18morphology TSR is the most widely used type in the US and European countries RSS is a smoked rubber sheet and largely used in industry
Figure 1.4 Natural rubber manufacturing process [5]
Trang 19Figure 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 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 ground water are mostly used Previous study reported that in Vietnam 25 m3 wastewater is discharged from the production of 1 ton of RSS from fresh latex, whereas approximately 18 m3 wastewater is discharged to produce 1 ton of CL [7] This wastewater heavily polluted, and it is causes 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 wastewaters because this wastewater
Trang 2020,000 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 been widely used for field latex coagulation in Vietnam Specifically, the natural rubber processing wastewater collected from the coagulation process at a rubber processing factory 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 of ammonia (e.g., 100 mg-N·L-1 to 1,000 mg-N·L-1) Ammonia is added to the latex in the tapping cups and collecting buckets to increase the pH of the latex to prevent premature 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 largest sources of industrial wastewater pollution in Southeast Asian countries, and usually, specific and strict effluent standards are established for natural rubber processing factories In 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 Table 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 water supply) The national technical regulations published 2015 contain two categories: new factories (started operation after 31/March/2015) and existing factories (started operation before 31/March/2015)
Trang 22Table 1.2 National technical regulation on the effluent of natural rubber processing
industry in Vietnam
(QCVN 01-MT: 2015/BTNMT)
Trang 231.2 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 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 an 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]
Trang 241.2.1 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 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 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
Trang 251.2.2 Upflow anaerobic sludge blanket reactor
A UASB 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 of well settleable sludge aggregates and the application of a reverse funnel-shaped internal gas-liquid-solids separation (GSS) devise are key technologies for a successful UASB reactor (Figure 1.7) The characteristics of the UASB are listed below
1) The influent is fed from a bottom reactor in order to create upflow
2) 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 a 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 reactor compared with that from an activated sludge process
Table 1.4 summarizes the process performance of the UASB 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) as 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 as accumulated rubber particulates in the UASB 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
Trang 26UASB reactor increased to 96.5 ± 2.6%, with a methane recovery rate of 84.9 ± 13.4%, for natural rubber processing wastewater in Vietnam [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 a 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-3·d-1 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
Trang 27Figure 1.7 Schematic diagram of UASB reactor
Two stage Thailand 24.8
Two stage Thailand 997 + 597
manure sludge 28.5 79.8-87.9% Nguyen (1999)
Anaerobic digester trating casava wastewater 2.65 96.5 ± 2.6 Thanh et al., (2015)
Concentrated latex mill 1.41 82 Jawjit and Liengcharernest (2010)
Anaerobic pond
in the rubber factory 0.8 96.57 ± 1.3 Tanikawa et al., (2016)
Trang 281.2.3 Anaerobic baffled reactor
An anaerobic baffled reactor (ABR) has been designed since the early 1980s and has several advantages over well-established system such as UASB reactor and anaerobic filter [16] These advantages are better resilience to hydraulic and organic shock loadings, longer biomass retention times, lower sludge yields, and the ability to partially separate the various phases of anaerobic catabolism The most significant advantages of the ABR is the typical reactor configuration that can separate acetogen and methanogen longitudinally down the reactor This two phases operation can enhance acetogen and methanogen activity by a factor of up
to four as acetogen accumulate within the first stage, and different microbial group can develop under more favorable conditions Therefore, the ABR has been applied to treatment of various industrial wastewaters
Figure 1.8 shows that various reactor configuration of ABR Since ABR was proposed, several types reactor configuration was designed The first report of ABR was equipped several partitions in the reactor to keep high concentration of methanogens This study reported the methane recovery rate was increased to 30 ~ 55% in organic loading rate of 1.6 kg-COD·m-3·day-1 [16] Figure 1.8 (A) is basic design of ABR that 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 retention time of waste solid In Figure 1.8 (C), the diameter of downflow compartment made narrow, the increased sludge retention time in the up-flow compartment
Akunna and Clark (2000) reported the performance of a granular-bed anaerobic baffled reactor (GRABBA) applied in the treatment of a whisky distillery wastewater [17] The GRABBA used granular sludge for inoculation and its can
Trang 29compatible with the both advantage of UASB reactor and ABR This GRABBA can accepted high OLR as well as high energy recovery form as the methane
Application of ABR to natural rubber processing wastewater was reported by Saritpongteeraka and Chaiprapat (2008) The research reported ABR had high COD and sulfate removal efficiencies at HRT of 10 days In addition, they examined pH adjustment by using parawood ash as low-cost reagent
Trang 30Figure 1.8 Various reactor configuration of ABR [16]
Trang 311.2.3 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 bio reactor; a settling tank (“final clarifier”) for the separation of solids and treated waste water in the activated sludge; and a return activated 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 a mixture of primary treated or screened sewage combined with organisms to develop
a biological floc This aeration process requires a huge amount of electricity The aeration 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 a 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 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
Trang 321.2.4 Swim bed tank
The swim-bed technology, involving a novel acryl-fiber biomass carrier- biofringe, is a new approach for wastewater treatment, especially for the high-rate treatment of organic wastewater Nguyen et al (2012) examined a laboratory-scale swim-bed technology for latex wastewater and found good organic removal and nitrification at an OLR of 1.0 kg ·m-3·day-1 [4]
1.2.5 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 a sponge- based bioreactor, as a novel cost-effective post-treatment method for anaerobically pre-treated sewage [18] Many research papers on the performance of DHS reactors for treating sewage have been published [19-27] To date, six types of sponge 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 has the ability to 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 been applied to treat effluent from the anaerobic tank treatment
of natural rubber processing wastewater [20] This system efficiently removes organics and nitrogen, but it requires a long HRT and large treatment area, as do conventional aerated tanks
Figure 1.11 presents a summary of the sixth sponge carriers developed for DHS reactors Currently, the G-3 type sponge is widely used because of its high process performance The highlight of the DHS reactor is that it can be operated without aeration or with low aeration requirements, as oxygen is naturally dissolved
in wastewater In addition, the sponge media support a large amount of biomass as
Trang 33well 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 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 of industrial wastewaters, especially the post-treatment of UASB reactor-treated high-strength industrial wastewater [23][24] Several studies have reported the treatment of molasses wastewater using a UASB-DHS system [34-36] Moreover, the DHS reactor has been applied to treat reactive dye wastewater [26], freshwater aquariums [27] [28], and ethylene glycol-containing industrial wastewater [29]
Figure 1.10 Principle of downflow hanging sponge reactor and full-scale DHS in India
Trang 34Figure 1.11 Development history from DHS G1 to DHS G6 [30]
1.2.6 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 the 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 low turbidity and high color for drinking water treatment In natural rubber processing wastewater treatment, the DAF process can achieve a high removal efficiency of suspended solids, but the high cost of this process prevents its wide application [7]
Trang 35an 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 over conventional 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 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 wastewater is expected
Trang 361.2.8 Combination of treatment system for natural rubber processing wastewater
Table 1.5 summarizes the wastewater treatment technologies for natural rubber processing wastewater Each process has advantages and disadvantages For natural rubber processing wastewater treatment, several wastewater treatment systems are combined in order to meet the 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 ditch UASB
Activated sludge
Swim-bed technology
Dissolved air floatation MBROrganic removal
effciency
High (more than 90%) High High High above 90% Low HighEffluent quality Low High Low High High Low High
nutrient
recovery
Trang 371.3 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 treatment 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 system and can be applied at any scale and in almost any place The main benefit of the anaerobic wastewater treatment process is that useful energy in the form of methane can be recovered In general, 40 ~ 45 m3 of biogas can 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 et al (2008) summarized the reasons for selecting an anaerobic wastewater treatment process, identifying striking advantages of the anaerobic wastewater treatment process over the conventional aerobic treatment processes (Table 1.6) [32]
Table 1.6 Benefits of anaerobic treatment process
· Reduction of excess sludge production up to 90% compared with 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
Trang 38depending on aeration efficiency
· Production of about 15.5 MJ CH4 energy·kg-COD-1 removed, giving 1.4 kWh electricity (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 and low-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
Trang 39In 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 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
occursat 3,500 mg-N·L-1 under mesophilic conditions and at 2,000 mg-N·L-1 under
Trang 401.3.2 Anaerobic industrial wastewater treatment technology
During the last 40 years, anaerobic wastewater treatment technology has evolved from localized lab-scale experiments to the successful worldwide implementation 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 wastewaters [34] Specifically, these processes are widely applied in some agro-food industries 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 wastewaters containing toxic compounds or wastewaters with a complex composition
Table 1.7 Application of anaerobic technology to industrial wastewater [33]
Industrial sector Type of wastewater
Installed reactors (% of total) Agro-food
industry
Sugar, potato, starch, yeast, pectin, citric acid, cannery confectionary, fruit, vegetables, dairy, bakery
36 Beverage Beer, malting, soft drinks, wine, fruit juices, coffee 29 Alcohol distillery Can juice, cane molasses, beet molasses, grape wine, grain fruit 10 Pulp and paper
industry
Recycle paper, mechanical pulp, NSSC, sulphite pulp, straw, bagasse
11 Miscellaneous Chemical, pharmaceutical, sludge liquor, landfill leachate, acid
mine water, municipal sewage
14