Anaerobic treatment of low strength wastewaters in temperate regions

In this study, two identical lab-scale Upflow Anaerobic Sludge Bed Reactors (UASBR) with an effective volume of 6.45 l were used and operated as continuous systems for about 12 months. The mesophilic UASBR was operated at 35°C±2.0°C, whereas the psychrophilic UASBR was operated at room temperature to start with and reduced to around 10°C step by step. In the study, synthetic wastewater characterizing domestic sewage was fed to the reactors. Results indicated around 80% COD removal at 16°C at a HRT of 4.8 h, while at the same HRT the COD removal could be observed above 85% at 35°C. The total biogas productions were observed about the same amount between the HRT's of 10-4 h in both reactors. However, when the temperature in the psychrophilic reactor was reduced to 10°C, total biogas production decreased significantly at the beginning, but improved afterwards. The average methane content in the psychrophilic reactor was always found higher (93%) than it was in the mesophilic reactor (90%). Although the COD removal at 10°C decreased to 74%, anaerobic treatment of low strength wastewaters could be well established and a more feasible system due to no heating requirement could be achieved successfully.