Previous studies have reported the application of the UASB reactor for the treatment of natural rubber processing wastewater.. New contributions of the thesis - Current environmental iss
Trang 1MINISTRY OF EDUCATION AND TRAINING
HANOI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Trang 2This dissertation was finalized at Hanoi University of Science and Technology
Supervisors:
1 Assoc Prof Nguyen Minh Tan
2 Prof Takashi Yamaguchi
This dissertation could be found at:
1 Ta Quang Buu Library - Hanoi University of Science and Technology
2 National Library of Vietnam
Trang 3A INTRODUCTION OF THESIS
1 Research Topics
Natural rubber is one of the most valuable agricultural products in Southeast Asian countries However, local natural rubber processing industry discharges large amounts of wastewater from several manufacturing processes such as coagulation, centrifugation, lamination, washing, and drying This wastewater contains high concentrations of organic compounds, nitrogen, as well as other contaminants The factories in Southeast Asian countries commonly utilize a combination of anaerobic-aerobic lagoon systems for treating this wastewater The existing treatment systems have shown high chemical oxygen demand (COD) removal efficiency However, they require a large area
of lagoon, high operating costs (especially for surface aeration), and long hydraulic retention times (HRTs) In addition, the existing treatment system also requires improvements to the effluent water quality in order to conform to the discharge standards set Previous studies reported that the system achieved the Vietnamese industrial effluent standard B However, environmental problem has been seriously in Vietnam Therefore, the effluent quality of existing system should be improved as soon
as possible
An upflow anaerobic sludge blanket (UASB) reactor is one of the most promising systems, given its high organic loading rate (OLR), low operational costs, and energy recovery in the form of methane for the treatment of different kinds of industrial wastewater 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 remaining natural rubber particle is essential The effluent from the UASB reactor treating high-strength industrial wastewater still contained high concentrations of organic compounds and nutrients Thus, an aerobic treatment system has been typically applied as post-treatment to remove residual organic matter and achieve effluent standards
2 Research objectives and contents of the thesis
- Development of energy recovery type wastewater treatment system for natural rubber processing wastewater in Vietnam
- Establishment of optimal treatment system for natural rubber processing wastewater treatment in Vietnam
Trang 43 New contributions of the thesis
- Current environmental issues and treatment systems for natural rubber processing wastewater in Vietnam were characterized via not only literature review but field study and systemized
- A novel treatment system, i.e BR-UASB-DHS, was developed in order to treat wastewater with high organic pollution and recover biogas as energy
4 The layout of the thesis
The thesis has 99 pages in total and consisted by introduction: 2 pages, Chapter 1: 24 pages for state of art, Chapter 2: 13 pages for Materials and Methods, Chapter 3: 43 pages for Results and Discussion, Chapter 4: 2 pages for Conclusions and 80 of references
Trang 5B CONTENT OF THE THESIS
1 State of art
1.1 Natural rubber
Natural rubber has good wear resistance, high elasticity, high resilience and tensile strength
It has a good dynamic performance and low level of damping Therefore, natural rubber has been widely used for carpet underlay, adhesives, foam, balloons and medical accessories such as rubber gloves The consumed total rubber amount on 2017 reached to 28,287,000 ton and it was 3% increase compared with 2016 (IRSG report) Natural rubber production on 2017 has been increased
to 13,380,000 ton Thailand and Indonesia produced over 60% of total natural rubber production The consumed total rubber amount on 2017 reached to 28,287,000 ton and it was 3% increase compared with 2016 (IRSG report) Natural rubber production on 2017 has been increased to 13,380,000 ton Thailand and Indonesia produced over 60% of total natural rubber production The production process of natural rubber products such as coagulation, centrifugation, lamination, washing and drying used a large amount of fresh water and discharged same amount of wastewater These wastewaters mainly contain wash water, small amounts of uncoagulated latex and serum with small quantities of protein, carbohydrates, lipids, carotenoids and salts
Figure 1.1 Top natural rubber produced countries on 2014 over the world
Trang 61.2 Current treatment technology for natural rubber processing wastewater
The aerated lagoon and ponds have been commonly used for treatment of this wastewater
On the other hand, the application of advanced treatment processes such as dissolved air flotation (DAF) and upflow anaerobic sludge blanket (UASB) have been limited The aerated lagoon can perform high organic removal efficiency with low operational costs and installed cost This process
is most popular treatment system for natural rubber processing wastewater in Vietnam Currently, this process was combined with the rubber trap and/or anaerobic lagoon, and achieved the effluent standard or water quality in the final effluent water in Vietnamese Standard B However, the local factory consumed large amount of electricity for wastewater treatment even higher than natural rubber production In addition, greenhouse gas (GHG) emission from oxidation ditch process would concern due to low dissolved oxygen concentration and low C/N ratio in natural rubber processing wastewater
Trang 81.3 Biological industrial wastewater treatment process
Anaerobic digestion is more attractive wastewater treatment process compared with aerobic wastewater treatment process The bioreactor of anaerobic wastewater treatment process is very simple system and can be applied any scale and at almost any place Most great benefit of anaerobic wastewater treatment process is useful energy in the form of methane can be recovered by anaerobic digestion In general, 40 ~ 45 m3 of biogas can recovered from 100 kg-COD of influent 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 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 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 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 processing factories Nguyen et al (2016) reported that the granulation was enhanced with the use of aluminum chloride, and the total COD removal efficiency of the UASB reactor increased to 96.5 ± 2.6%, with a methane recovery rate of 84.9 ± 13.4%, for natural rubber processing wastewater in Vietnam An aerobic treatment is the removal process that oxidize organic compounds, ammonia, smell and iron by several aerobic bacteria under the oxygen available condition The bacteria or floc absorbed organic compounds and degrade to water and carbon dioxide to get energy for own breeding
Table 1.4 Application of UASB reactor for natural rubber processing wastewater treatment
Reactor type Volume Seed sludge Organic removal rate COD removal
Single Vietnam 8.55
Digested pig manure sludge 28.5 79.8-87.9% Nguyen (1999)
Single Vietnam 17
Anaerobic digester trating casava wastewater 2.65 96.5 ± 2.6 Thanh et al., (2015)
Two stage Thailand 24.8
Concentrated latex mill 1.41 82 Jawjit and Liengcharernest (2010)
Two stage Thailand 997 + 597
Anaerobic pond
in the rubber factory 0.8 96.57 ± 1.3 Tanikawa et al., (2016)
Reference
Trang 91.4 Greenhouse gas emission from wastewater treatment system
A GHG is a gas that absorbs and emits radiant energy within the thermal infrared range The primary GHGes in Earth's atmosphere are water vapor, carbon dioxide, methane, nitrous oxide and ozone Global warming potential (GWP) is to compare the amount of hear trapped by a certain mass of the gas in question to the amount of heat trapped by a similar of carbon dioxide The wastewater treatment plant also emitted considerable GHG to atmosphere Approximately 3.4% of GHG emitted from waste disposal and treatment process
2 Material and methods
2.1 Filed survey
The wastewater treatment system in a local natural rubber manufacturing factory in Binh Duong province, Vietnam was surveyed The greenhouse gases emission from an anaerobic lagoon was collected by using a collection chamber made from polyvinyl chloride pipes and analyzed by GC-TCD and GC-ECD
2.2 Laboratory UASB-DHS system
Raw wastewater was collected from the coagulation process in a natural rubber factory producing SVR in Thanh Hoa Province, Vietnam The laboratory-scale treatment system was operated in Hanoi University of Science and Technology, Vietnam
2.3 Laboratory scale ABR system
The anaerobic baffled reactor (ABR) made up of polyvinyl chloride pipes (diameter: 110
mm, height: 1,000 mm) had 10 compartments and working volume of 68 L
2.4 Pilot UASB-DHS system
The pilot scale natural rubber processing wastewater treatment system installed at the Rubber Research Institute of Vietnam, Binh Duong, Vietnam The system consisted of an ABR (76.5
m3), a substrate reservoir (5 m3), a UASB reactor (3 m3), a settling tank (ST; 1 m3), and a down-flow hanging sponge (DHS) reactor (2 m3) with an effluent recirculation
2.5 Analysis
Trang 10The measurement methods of pH, DO, ORP, COD, BOD, SS, TN, ammonia, nitrite, nitrate, volatile fatty acid, biogas production and composition was described
3 Results and discussions
3.1 Characterization of current wastewater treatment system
The system consisting baffled tank, aero tank and facultative lagoon used for treatment of natural rubber wastewater in Binh Duong province, Vietnam was surveyed to investigate current treatment process The wastewater quality in several sampling points was shown in Table 3.1 The aerobic tank was not operated well due to the electricity cost for surface aeration The effluent quality of this factory was largely exceeded the effluent standard The wastewater treatment plant is known one of big GHGs emission source However, GHGs emission from natural rubber processing wastewater treatment plant is not reported Thus, we measured GHG emission from current anaerobic tank treating natural rubber processing in Binh Duong province, Vietnam Figure 3.2 shows the composition of the biogas collected from compartments 28, 33, and 56 using the water substitution method during the survey in October (Figure 2.1)
Figure 2.1 Schematic diagram of open-type anaerobic system
The emitted gas from the open-type anaerobic tank comprised 57.7%-60.8% methane, 14.5%-31.5% carbon dioxide, 10.8%-24.7% nitrogen, and 329-423 ppm of nitrous oxide The nitrous oxide emission from natural rubber processing wastewater treatment system was firstly observed
We considered that ammonia was oxidized to nitrate and nitrite at the surface of the open-type anaerobic tank; therefore, nitrate and nitrite promptly were consumed by denitrification Finally, 18.1% of the ammonia was removed in the open-type anaerobic tank, and the nitrous oxide emission factor became 0.0263 kg-NO2-N·kg-N-1 This emission factor was much higher than 0.005 kg-NO2-N·kg-N-1, which is the emission factor for the direct emissions from wastewater treatment plants applied by IPCC (2006) and similar to the emission factor for full- scale biological nutrient removal wastewater treatment plants The emission rates (flux) from 1 m3 of treated RSS wastewater
-3
Trang 11CO2eq·m-3, and 0.153 t-CO2eq·m-3, respectively These emission rates were higher than the emission rates from the aerobic wastewater treatment system in cap lump processing factories
Table 3.1 Water quality in each sampling point at a local natural rubber processing
wastewater in Vietnam
Figure 3.2 Biogas composition of compartment 28, 33 and 56
Figure 3.6 Composition of emitted GHGs from near the influent part, the center part, and the effluent
part of the OAS
Trang 12Figure 2.2 Gas sampling system used in this study
3.2 Development concept of a laboratory scale UASB-DHS system for natural rubber
processing wastewater treatment
As previous research reported the application of UASB reactor for natural rubber processing wastewater was failed due to large amount of residual natural rubber accumulated in the UASB column Therefore, development of efficient natural rubber removal (recovery) process is essential for successful to apply UASB reactor Baffled reactor can be recovered solid by its unique design and considered effective pre-treatment process for natural rubber process wastewater Thus,
we designed the wastewater treatment process for natural rubber processing wastewater consisted by
BR, UASB reactor and DHS reactor (Figure 2.4)
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– 8) sampling ports, (9) UASB column, (10) Gas solid separator, (11) mixer, (12) desulfurizer, (13) gas meter, and (14) distributor.
Trang 13The system showed good performance in the start-up period of phase 1 (days 1–45), and was operated for a total of 126 days The influent of pH was 5.8 ± 0.7 and 5.3 ± 0.3, respectively and the proposed baffled reactor (BR)-UASB-DHS system performed without pH adjustment Overall, high total COD removal of 98.6 ± 1.2% and TSS removal of 98 ± 1.4% were achieved with an HRT
of 42.2 h Figure 3.9 shows the COD mass balance of the influent reactor, BR, and UASB reactor during phase 2 The BR steadily removed 42.3 ± 34.5% of TSS and 72.4 ± 38.2% of VSS during phase 2 Similarly, solid COD was removed, and the concentrations of acetate and propionate increased Therefore, the BR acted as both a trapping tank for the residual rubber particles and an acidification tank The UASB reactor also performed at a high total COD removal efficiency of 92.7
± 2.3% with an OLR of 12.2 ± 6.2 kg-COD·m-1·day-1 The methane recovery rate, calculated from the removed total COD, was 93.3 ± 19.3% for phase 2 High-level COD removal efficiency and methane recovery rates are thought to result from the efficient solid organic removal and acidification of the wastewater by the BR The BR–UASB–DHS system can decrease the HRT; consequently, the land requirements of the system are smaller than those of currently used treatment systems