Two-stage Upflow Anaerobic Sludge Blanket Research Articles

Process Improvement of a Two-Stage Upflow Anaerobic Sludge Blanket System by Micronutrient Supplement in Relation to Sulfur Transport

The main purpose of this research was to elucidate the influence of the addition of iron alone (0–100 ppm) or with 2 ppm each of cobalt, copper, and nickel on the performance of a two-stage UASB system treating ethanol wastewater. The system consisted of two reactors connected in series. The system was maintained at a fixed chemical oxygen demand loading rate (16 kg/m3d) and 37 °C with a recycle ratio of 1:1. Both Co and Ni were found to be deficient in the ethanol wastewater, while Fe and Cu became inadequate in two-stage UASB. The addition of Fe provided dual benefits of a reduction in both sulfide toxicity and hydrogen sulfide content in produced gas, resulting in marginally improved hydrogen and methane productivities. When the Fe dosage was increased beyond the optimum value of 50 ppm, the process performance drastically declined, as a result of high total volatile fatty acid concentrations that inhibited acidogens and methanogens predominantly present in the 1st and 2nd reactors, respectively. The chemical precipitation of iron sulfide was responsible for the reduction of produced H2S in both aqueous and gaseous phases. The addition of 2 ppm each of Co, Cu, and Ni together with 50 ppm Fe resulted in an enhanced process performance, as indicated by the improved CH4 yield (mL/g COD applied) to about 42.3% compared to that without micronutrient supplement. Supplementation to fulfill the sufficiency of all micronutrients was vital for the maximization of anaerobic digestion (AD) performance, as generally indicated in methanogenic activity.

The recycling of biodigested vinasse in an upflow anaerobic sludge blanket reactor is a feasible approach for the conservation of freshwater in the biofuel ethanol industry

The generation of large volumes of vinasse during the production of biofuel ethanol is a challenging problem since inappropriate application of the byproduct as an agro-fertigant can give rise to contamination of soil and watercourses and cause harm to aquatic life. The aims of the study were(i) to evaluate an alternative strategy involving the generation of biogas by anaerobic digestion of sugarcane vinasse in two-stage upflow anaerobic sludge blanket (UASB) reactors (R1 and R2 connected in series), and (ii) to determine the ethanol content and fermentation efficiency of mashes prepared by diluting sugarcane molasses with deionized water, fresh vinasse and effluents from R1 or R2, both before and after submission to the Fenton reaction. The highest percentages of ethanol were obtained with fermentation mashes prepared from molasses diluted with Fenton-treated R1 (5.1%) or R2 effluents (5.7%) or with non-treated R2 effluent (5.7%). The corresponding fermentation efficiencies of these processes were 88.5, 92.1 and 89.3%. The proposed combination of biofuel and biogas production would provide a sustainable source of energy, contribute to the safe disposal of large quantities of vinasse and help to reduce the volume of freshwater employed by the sugarcane processing industry.

Purified Terephthalic Acid Wastewater Treatment Using Modified Two-Stage UASB Bioreactor Systems.

Microbial community dynamics and PTA wastewater degradation performance of sequentially connected two-stage upflow anaerobic sludge blanket (UASB) bioreactors have been studied for 225days. The working volume of acidogenic (R1) and methanogenic reactors (R2) have sixfold differences. Thus, the reactors operated under different hydraulic retention time (HRT) conditions, which are preferential for PTA wastewater content. Archeal and bacterial profiles of granules were analyzed with denaturing gradient gel electrophoresis (DGGE) and real-time quantitative PCR (Q-PCR) techniques. According to high-pressure liquid chromatography (HPLC) results, 4-Carboxybenzaldehyde (4-CBA) and acetic acid (AA) completely degraded in the first stage, whereas terephthalate (TA) and p-toluic acid (p-TA) degradation ratios were 90% and 47% in the second stage, respectively. The methane content of the UASB reactor was determined as 76% by gas chromatography (GC) analysis. Microbial community analysis indicated that the members of hydrogenotrophic methanogen groups Methanobacteriales and Methanomicrobiales were dominantly responsible for methane production throughout the process.

Application of in-situ H2-assisted biogas upgrading in high-rate anaerobic wastewater treatment

The H2-assisted biogas upgrading approach has recently attracted much interest as a low-cost and environmentally friendly alternative to commonly used ex-situ/ physiochemical biogas upgrading techniques. However, most studies conducted to date have been limited to anaerobic solid-waste treatment characterized by flocculant sludge and low organic loading rates (OLR). In an attempt to expand its application to high-rate anaerobic wastewater treatment, an innovative two-stage up-flow anaerobic sludge blanket reactor system was employed using anaerobic granular sludge. We found that the CH4 content of product gas was consistently >90% and that H2 and CO2 concentrations stayed below 5%, even when OLR was increased from 1 to 5 g L−1 d−1 and H2 feeding rates were increased from 0.13 to 0.63 g L−1 d−1. We were also able to show that CO (5–10%) in H2-rich syngas didn’t inhibit methanogenesis or had significant impact on microbial community structure, suggesting that H2-assisted biogas upgrading with H2-rich syngas is feasible.

Improving the energy balance of ethanol industry with methane production from vinasse and molasses in two-stage anaerobic reactors

Abstract Thermophilic anaerobic digestion is a viable option for processing sugarcane vinasse that recovers energy in the form of methane. However, restarting real-scale vinasse-treating reactors, at the resumption of the sugarcane harvest season, can lead to difficulties, making it desirable to keep them in continuous operation in the off-season. Thus, was evaluated the thermophilic anaerobic conversion of sugarcane vinasse in a two-stage upflow anaerobic sludge blanket (UASB) reactor (reactors R1 and R2), employing sugarcane molasses in the off-season for methane production, followed again by vinasse in the following harvest season. UASB reactor R2 yielded a higher methane percentage in biogas and higher volumetric methane production rates and methane yield than R1, accounting for a 58% increase in energy production in the two-stage system compared to the single-stage system using vinasse. It is observed that the molasses is an important source of carbon for the energy production using the thermophilic UASB reactors (18.01 MJ L−1 molasses), compared to alcoholic fermentation (8.30 MJ L−1 molasses). The methane produced in the reactors system (R1 + R2), after the off-season, can generate 5.1 kWh d−1 per m3 of vinasse, or 17% of the electricity needed to process a ton of sugarcane.

Separate production of hydrogen and methane from cassava wastewater with added cassava residue under a thermophilic temperature in relation to digestibility

In this research, the separate production of hydrogen (H2) and methane (CH4) from cassava wastewater with added cassava residue was investigated using a two-stage upflow anaerobic sludge blanket (UASB) system under thermophilic temperature (55 °C) in a continuous mode of operation and steady state condition. The two-stage UASB system was operated under an optimum chemical oxygen demand (COD) loading rate of 10.29 kg/m3d (based on the total volume of both bioreactors) of the cassava wastewater with different concentrations of added cassava residue. The recycle ratio of the effluent from the second bioreactor to the feed flow rate was fixed at 1:1 (v/v). In addition, the solution pH in the first bioreactor was controlled at 5.5, while that in the second bioreactor was not controlled. Under the optimum cassava residue concentration of 1200 mg/L, the produced gas from the first bioreactor contained 42.3% H2, 55% carbon dioxide (CO2) and 2.70% CH4, while that from the second bioreactor contained 70.5% CH4, 28% CO2 and 1.5% H2. Apart from a high H2 and CH4 production performance (45.2 and 150% improvement, respectively, as compared to the system without added cassava residue) under the optimum cassava residue concentration (1200 mg/L) and the controlled COD loading rate (10.29 kg/m3d) of the cassava wastewater, the degradation performance of cellulose and hemicellulose were 41% and 22%, respectively, for the first bioreactor and 23% and 11%, respectively, for the second bioreactor. The digestibility of the cassava residue at thermophilic operation was higher than that at mesophilic temperature.

Predominance of syntrophic bacteria, Methanosaeta and Methanoculleus in a two-stage up-flow anaerobic sludge blanket reactor treating coffee processing wastewater at high organic loading rate

The effect of the organic loading rate (OLR) on the performance and microbial composition of a two-stage UASB system treating coffee processing wastewater was assessed. The system was operated with OLR up to 18.2 g COD (L d)−1 and effluent recirculation. Methane production and effluent characteristics were monitored. The microbial composition was examined through next-generation sequencing and qPCR from the anaerobic sludge of the first reactor (R1) operated at low and high OLR. The system showed operational stability, obtaining a maximum methane production of 2.2 L CH4 (L d)−1, with a removal efficiency of COD and phenolic compounds of 84 and 73%, respectively. The performance of R1 at high OLR in steady conditions was associated with an appropriate proportion of nutrients (particularly Fe) and a marked increase of the syntrophic bacteria Syntrophus and Candidatus Cloacimonas, and acetoclastic and hydrogenotrophic methanogens, mainly Methanosaeta, Methanoculleus, Methanobacterium and Methanomassiliicoccus.

Role of organic loading rate in bioenergy generation from palm oil mill effluent in a two-stage up-flow anaerobic sludge blanket continuous-stirred tank reactor

This contribution presents the technical possibilities for continuous hydrogen and methane production using an optimum organic loading rate of palm oil mill effluent in a two-stage reactor at a thermophilic temperature of 55 °C. The influence of four organic loading rates, namely, 30, 40, 50, and 60 kg COD/(m3 d) for hydrogen production and 8.3, 10.2, 13.1, 15.8 kg COD/(m3 d) for methane production, were investigated. Hydrogen production was controlled in an up-flow anaerobic sludge blanket reactor at a constant hydraulic retention time of 12 h. The maximum hydrogen content, volumetric hydrogen production rate and hydrogen yield were found to be 45%, 2.5 L H2/d and 33.48 mL H2/g COD, respectively, at the organic loading rate of 50 kg COD/(m3 d). The effluent from the hydrogenogenic reactor was further digested into methane in the continuous stirred tank reactor at a hydraulic retention time of 5 d. The maximum volumetric methane production rate and methane yield were 10.58 L CH4/d. and 0.11 m3 CH4/kg COD, respectively, at an organic loading rate of 13.1 kg COD/(m3 d). A total chemical oxygen demand removal of 91% was achieved in this two-stage process. The scientific contribution of this two-stage technology with an optimized organic loading rate may play a significant role in degrading palm oil mill effluent and developing an energy-efficient strategy for waste management.

REVIEW ON BIODEGRADABLE KITCHEN WASTE MANAGEMENT

With the rapid urbanization managing of the kitchen waste generated by the large population has become a big problem. Kitchen wastes comprises of vegetables peels, fruit peels, smashed fibre of fruits, spare uneaten food items, food grains etc. These are loaded with nutrients and organic material, and can be easily recycled. In recent years, researchers have explored the various methods of extraction of biogases like Hydrogen, Methane, etc. from these biodegradable wastes. This paper reviews the various research works carried out on the synthesis of kitchen waste using anaerobic digestion process, biomethanation or composting. Hydrogen, a valuable gas is produced through the anaerobic fermentation of domestic organic waste in the absence of pretreatment or photo-fermentation, or bioaugmentation of indigenous fermentative communities. Chronological dark and photo fermentation process is also an emerging way studied for production of bio-hydrogen using kitchen waste. Esterification and hydrolysis process has also been utilized to synthesize kitchen waste forming Lactic acid. Thermo-chemical Hydrolysis of Kitchen Waste through optimization of temperature, time and chemical compositions, Fourier Transform Infrared Spectroscopy, microaeration process are studied resulting in bio-fuel production. Methane formation combining Kitchen Waste and black water using two-stage upflow anaerobic sludge blanket (UASB) septic tanks at the lower temperatures has also been studied and it appears to be more efficient than using only Black Water. Organic acids produced from anaerobic digestion of kitchen waste using an integrated method consisting of freezing, thawing, centrifugation, filtration and evaporation. Thus this review paper deals with the study of various methodologies of kitchen waste utilization.

Treatment of natural rubber processing wastewater using a combination system of a two-stage up-flow anaerobic sludge blanket and down-flow hanging sponge system.

A pilot-scale experiment of natural rubber processing wastewater treatment was conducted using a combination system consisting of a two-stage up-flow anaerobic sludge blanket (UASB) and a down-flow hanging sponge (DHS) reactor for more than 10 months. The system achieved a chemical oxygen demand (COD) removal efficiency of 95.7% ± 1.3% at an organic loading rate of 0.8 kg COD/(m(3).d). Bacterial activity measurement of retained sludge from the UASB showed that sulfate-reducing bacteria (SRB), especially hydrogen-utilizing SRB, possessed high activity compared with methane-producing bacteria (MPB). Conversely, the acetate-utilizing activity of MPB was superior to SRB in the second stage of the reactor. The two-stage UASB-DHS system can reduce power consumption by 95% and excess sludge by 98%. In addition, it is possible to prevent emissions of greenhouse gases (GHG), such as methane, using this system. Furthermore, recovered methane from the two-stage UASB can completely cover the electricity needs for the operation of the two-stage UASB-DHS system, accounting for approximately 15% of the electricity used in the natural rubber manufacturing process.

Hydrogen and methane production from cassava wastewater using two-stage upflow anaerobic sludge blanket reactors (UASB) with an emphasis on maximum hydrogen production

The objective of this study was to produce hydrogen and methane from cassava wastewater using two steps of upflow anaerobic sludge blanket reactors (UASB), emphasizing maximum hydrogen production. For the first hydrogen production stage, the UASB system was operated at 37 °C and pH 5.5 at different COD loading rates. A maximum specific H2 production rate of 0.39 l H2/l d and a maximum H2 yield of 39.83 l H2/kg COD removed were found at a COD loading rate of 25 kg/m3d and the gas produced contained 36.4% H2, and 63.6% CO2 without methane. For the second methane production stage, the UASB was fed by the effluent produced from the hydrogen production step operated at the optimum COD loading rate. A maximum specific CH4 production rate of 0.91 l CH4/l d and a maximum CH4 yield of 115.23 l CH4/kg COD removed were found at a COD loading rate of 8 kg/m3d. The inhibition levels of organic acids to acidogens and methanogens were found to be 10,000 and 400 mg/l as acetic acid, respectively.

Advanced nitrogen removal via nitrite from municipal landfill leachate using a two-stage UASB–A/O system

A system consisting of a two-stage up-flow anaerobic sludge blanket (UASB) reactor and an anoxic/aerobic (A/O) reactor was used to treat municipal landfill leachate. Denitrification took place in the first stage of the UASB reactor (UASB1). The chemical oxygen demand of the UASB1 effluent was further decreased in the second stage (UASB2). Nitrification was accomplished in the A/O reactor. When diluted with tap water at a ratio of 1:1, the ammonia nitrogen concentration of the influent leachate was approximately 1200mg·L−1, whereas that of the system effluent was approximately 8–11mg·L−1, and the corresponding removal efficiency is about 99.08%. Stable partial nitrification was achieved in the A/O reactor with 88.61%–91.58% of the nitrite accumulation ratio, even at comparatively low temperature (16°C). The results demonstrate that free ammonia (FA) concentrations within a suitable range exhibit a positive effect on partial nitrification. In this experiment when FA was within the 1–30mg·L−1 range, partial nitrification could be achieved, whereas when FA exceeded 280mg·L−1, the nitrification process was entirely inhibited. Temperature was not the key factor leading to partial nitrification within the 16–29°C range. The inhibitory influence of free nitrous acid (FNA) on nitrification was also minimal when pH was greater than 8.5. Thus, FA concentration was a major factor in achieving partial nitrification.

Optimization of separate hydrogen and methane production from cassava wastewater using two-stage upflow anaerobic sludge blanket reactor (UASB) system under thermophilic operation

The objective of this study was to investigate the separate hydrogen and methane productions from cassava wastewater by using a two-stage upflow anaerobic sludge blanket (UASB) system under thermophilic operation. Recycle ratio of the effluent from methane bioreactor-to-feed flow rate was fixed at 1:1 and pH of hydrogen UASB unit was maintained at 5.5. At optimum COD loading rate of 90kg/m3d based on the feed COD load and hydrogen UASB volume, the produced gas from the hydrogen UASB unit mainly contained H2 and CO2 which provided the maximum hydrogen yield (54.22mlH2/g COD applied) and specific hydrogen production rate (197.17ml/gMLVSSd). At the same optimum COD loading rate, the produced gas from the methane UASB unit mainly contained CH4 and CO2 without H2 which were also consistent with the maximum methane yield (164.87mlCH4/g COD applied) and specific methane production rate (356.31mlCH4/gMLVSSd). The recycling operation minimized the use of NaOH for pH control in hydrogen UASB unit.

Anaerobic-aerobic treatment of swine wastewater in uasb and batch reactors in series

In this work it was evaluated the performance of two systems of swine wastewater treatment consisting of two-stage upflow anaerobic sludge blanket (UASB) reactors, with and without post-treatment in sequencing batch reactor (SBR), fed continuously, with aerobic phase. The UASB reactors in the first stage had 908 L in the sets I and II, and in the second stage 350 and 188 L, respectively. In the set II the post-treatment was performed in a SBR of 3,000 L. The hydraulic detention times in the anaerobic treatment systems were 100, 75 and 58 h in the set I; 87, 65 and 51 h in the set II; and 240 and 180 h in the SBR. The volumetric organic load applied in the first stage UASB reactors ranged from 6.9 to 12.6 g total COD (L d)-1 in the set I and 7.5 to 9.8 g total COD (L d)-1 in the set II. The average removal efficiencies of total COD, total phosphorus (Ptotal), and Kjeldahl and organic nitrogen (KN and Norg) in the anaerobic treatment systems were similar and reached maximum values of 97%, 64%, 68%, and 98%. In the SBR, the removal efficiencies of total COD and thermotolerant coliforms were up to 62 and 92% resulting, respectively, in effluent concentrations of 135 mg L-1 and 2x10(4)MPN (100 mL)-1. For Ptotal, total nitrogen (TN) and Norg, the average removal efficiencies in the SBR were up to 58, 25 and 73%, respectively.

Anaerobic treatment of concentrated latex processing wastewater in two-stage upflow anaerobic sludge blanket

This study aims to investigate treatment performance of the two-stage upflow anaerobic sludge blanket (UASB) applied to concentrated latex processing wastewater in Thailand. First, optimal conditions including the hydraulic retention time (HRT) in the acid tank and the UASB tank, pH, and temperature (mesophilic and thermophilic) were determined. It was found that the HRT at 24 h and 48 h were the optimal HRT for the acid tank and the UASB tank, respectively. The pH of the system should be controlled at 7 to prevent rubber coagulation and to achieve high treatment performance, and the mesophilic condition (35°C) was found to be the optimal temperature. Second, the two-stage UASB was applied with the optimal conditions mentioned earlier with real wastewater at a latex mill. It was found that methane production was about 0·116 L CH4/g COD removed (16·3 – 22·8 m3CH4/d), and average chemical oxygen demand (COD) and suspended solids (SS) removal efficiency were about 82% and 92%, respectively. In case of SS removal, the results revealed that the two-stage UASB was capable of overcoming the limitations of the single-stage UASB in treating concentrated latex effluent. The results indicated that application of the two-stage UASB to concentrated latex processing wastewater is feasible. Nevertheless, combination with other treatment systems (e.g., oxidation pond, aerated lagoon) is necessary to meet Thailand's industrial effluent standards (in the case of COD).

Performance of Two-Stage Upflow Anaerobic Sludge Blanket Reactor Treating Wastewater from Latex-Processing Factory

AbstractIn this study, a relatively high-rate treatment (hydraulic retention time ≤2.5 days) of latex-processing wastewater was achieved in a two-stage upflow anaerobic sludge blanket reactor. A maximum acid production rate of 1.8 g L−1 d−1 acetic acid was obtained when the acidogenic reactor was operated over a hydraulic retention time (HRT) of 4 hr. Total chemical oxygen demand (COD) and sulfate removal efficiencies of the system were 51.6 and 75.9%, respectively, when the methanogenic reactor was operated over an HRT of 24 h. The specific acidogenic activity of granular sludge in the acidogenic and methanogenic reactor varied between 1.33–2.02 g COD g volatile suspended solids (VSS)−1 d−1, and the specific methanogenic activity ranged from 0.0078 to 0.0138 g COD-CH4 g VSS−1 d−1. Microbial diversity monitoring using the denaturing gradient gel electrophoresis technique revealed that there was more sulfate-reducing bacteria in both reactors than archea bacteria.

Two-stage UASB reactor converting coffee drink manufacturing wastewater to hydrogen and methane

In this study, the feasibility of a continuous two-stage up-flow anaerobic sludge blanket (UASB) reactor system, consisted of thermophilic (55 °C) dark fermentative H2 production and mesophilic (35 °C) CH4 production from coffee drink manufacturing wastewater (CDMW), was tested. A recently proposed operational strategy was used to overcome a major drawback of the long start-up period of the UASB reactor. Firstly, a completely stirred tank reactor (CSTR) was operated for 8 days to prepare seeding. The seed was then directly transferred to the UASB reactor. Microbial aggregation took place in the initial period, and the floc size was gradually increased over time. In UASB reactor, the maximum H2 yield of 2.57 mol H2/mol hexoseadded and a stable H2 production rate of 4.24 L H2/L/h were observed at a hydraulic retention time (HRT) of 6 h and substrate concentration of 20 g Carbo. COD/L. In this novel method using CDMW, thermophilic H2-producing granules with an average particle size of 1.3 mm was successfully developed after 100 days. The more bioenergy recovery was attempted in a post-treatment process using a mesophilic UASB reactor for CH4 production from the H2 fermented effluent. The maximum CH4 yield of 325 mL of CH4/g COD was achieved with removing 93% of the COD at an organic loading rate of 3.5 g COD/L/d. The developed two-stage UASB reactor system achieved biogas conversion by 88.2% (H2 15.2% and CH4 73%) and COD removal by 98%.

Sequential treatment of PTA wastewater in a two-stage UASB process: Focusing on p-toluate degradation and microbial distribution

Two-stage upflow anaerobic sludge blanket (UASB) process was investigated as an efficient process configuration option for the treatment of purified terephthalic acid (PTA) wastewater. To study its feasibility in a defined condition, synthetic wastewater containing only the major pollutants (i.e., acetate, benzoate, terephthalate and p-toluate) was used. By focusing the role of the second stage on the p-toluate degradation, improved overall COD and p-toluate removal capacities of 4.18 and 1.35 g-thCOD/L·day could be achieved together with a complete COD removal efficiency. In this situation, all the pollutants except p-toluate were completely degraded in the first stage while 38 and 62% of p-toluate originally present in the wastewater were consecutively degraded in the individual stages. The concomitant methane production rate in each stage was 0.91 and 0.35 L/L·day respectively, and the methane yield on p-toluate was determined to be 0.12 L/g-thCOD. Batch tests using the granules obtained from each stage revealed that the acidogenic microorganisms enriched in both stages had a universal ability to degrade all aromatic pollutants present in the PTA wastewater. Moreover, image analysis using scanning electron microscope and confocal laser scanning microscopy combined with fluorescence in situ hybridization technique elucidated that the distribution of acidogens and methanogens within the granule was varied in each stage, which influenced the mass transfer regime resulting in the different pollutant degradation rates during the batch tests.

Water-recycled Cassava Bioethanol Production Integrated with Two-stage UASB Treatment

Considering limited success in target-hitting discharge from alcohol industry, our attention was directed toward a recycling use of distillery spentwash (DS) in cassava bioethanol production by using a two-stage up-flow anaerobic sludge blanket bioremediation (TS-UASBB). With the TS-UASBB, SO 4 2−, COD, N and P in the effluent from the DS degraded significantly and their concentrations were kept at 0.2 g·L −1, 2.0 g·L −1, 1.0 g·L −1 and 15 mg·L −1, respectively, in 13 batch processes for water-recycled ethanol fermentation. With the effluent used directly as dilution water, no heat-resistant bacteria were found alive. The thirteen-batch ethanol production individually achieved 10% after 48 h fermentation. The starch utilization ratio and total sugar consumption were 90% and 99.5%, respectively. The novel water-recycled bioethanol production process with ethanol fermentation and TS-UASBB has a considerable potential in other starchy and cellulosic ethanol production.

Anaerobic treatment of concentrated latex processing wastewater in two-stage upflow anaerobic sludge blanketA paper submitted to the Journal of Environmental Engineering and Science.

This study aims to investigate treatment performance of the two-stage upflow anaerobic sludge blanket (UASB) applied to concentrated latex processing wastewater in Thailand. First, optimal conditions including the hydraulic retention time (HRT) in the acid tank and the UASB tank, pH, and temperature (mesophilic and thermophilic) were determined. It was found that the HRT at 24 h and 48 h were the optimal HRT for the acid tank and the UASB tank, respectively. The pH of the system should be controlled at 7 to prevent rubber coagulation and to achieve high treatment performance, and the mesophilic condition (35°C) was found to be the optimal temperature. Second, the two-stage UASB was applied with the optimal conditions mentioned earlier with real wastewater at a latex mill. It was found that methane production was about 0.116 L CH4/g COD removed (16.3–22.8 m3CH4/d), and average chemical oxygen demand (COD) and suspended solids (SS) removal efficiency were about 82% and 92%, respectively. In case of SS removal, the results revealed that the two-stage UASB was capable of overcoming the limitations of the single-stage UASB in treating concentrated latex effluent. The results indicated that application of the two-stage UASB to concentrated latex processing wastewater is feasible. Nevertheless, combination with other treatment systems (e.g., oxidation pond, aerated lagoon) is necessary to meet Thailand's industrial effluent standards (in the case of COD).