The processing performance of a high-strength-wastewater treatment system was investigated by feeding the system with sugar-containing synthetic wastewater for more than one year. The system consisted of a (35°C) mesophilic upflow anaerobic sludge blanket (UASB) reactor for pretreatment, and an ambient UASB reactor and a downflow hanging sponge (DHS) reactor for post-treatment. The DHS reactor was constructed using a liquid distributor and a packing material made with sponge cubes. A portion of the final effluent was recycled to the inlet of post-treatment with a recirculation ratio in the range of 2.0-0.3. The synthetic wastewater was made with organic waste from a food factory; it consisted of about 3,000mg of CODCr · l-1, 2,000mg of BOD · l-1 and 500mg of SS · l-1. The system exhibited excellent performance in organic removal, achieving 98% CODCr and 96% SS removal rates (final effluent: 43mgCODCr · l-1, 12mgBOD · l-1 and 15mgSS · l-1) with 75% of the methane recovered from the removed CODCr under conditions of 24hrs of HRT, a CODCr volumetric loading rate of 3.0 kg · m-3 · d-1 (35°C UASB as pretreatment, 1.4 kg · m-3 · d-1; post-treatment, 1.6 kg · m-3 · d-1), and low final effluent temperatures such as 1-10°C. The proposed system effectively saves energy and decreases the amount of excess sludge. It is considered as a novel process to treat high-strength wastewaters up to a discharge quality level.
