Effects of temperature and biomass concentration on the performance of anaerobic sequencing batch reactor treating low strength wastewater

The studies were carried out with simulated domestic wastewater (300±10 and 500 mg COD/L) and real domestic wastewater (290±10 mg COD/L). During these studies different organic loading rates (0.29, 0.82 and 1.1 kg COD/m3d for Set I and Set II, and 0.29 and 0.62 kg COD/m3d for Set III), hydraulic retention times (11, 15, 25 h), temperatures (10, 15, 25 °C) and at different anaerobic sludge concentrations (about 5, 10 g VSS/L) in the reactor were applied and the performance of the reactor was tested. It was observed that treatment of low strength wastewaters under low temperature was possible. Even at the lowest temperature applied and lowest sludge amount the total organic matter (COD) removal was 65.2%. However, the COD removal and methane production decreased with decreasing temperature and HRT. The COD removal efficiencies decreased when the system was fed with settled real domestic wastewater probably due to more complex structure of the domestic wastewater and the presence of suspended solids even in small concentrations. These results showed that the ASBR process can be used for treatment of low strength wastewaters at low temperatures.

Research Highlights
► Anaerobic sequential batch reactor is a promising treatment alternative for domestic wastewater, and can be operated effectively under low temperatures.
► The system achieved high COD removal efficiency (> 93%) at 9.6±0.4 gVSS/L.
► But, at 5.3±0.2 g VSS/L, the system performance decreased to 33%.
► Longer hydraulic retention time and cycle time were required at lower operational temperatures (>15 °C) and lower reactor VSS content.