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).
