The role of filter media in removing suspended and colloidal particles in an anaerobic reactor treating domestic sewage

A column packed with clean sheets of reticulated polyurethane foam was fed with either raw sewage, synthetic sewage or skimmed milk for a short time t o evaluate the mechanism of physical entrapment and filtration of particles . The results revealed that clean media were effective in the removal of su spended chemical oxygen demand (COD) (>75%) even with hydraulic retention t ime (HRT) as low as 0.5 h or upflow velocity as high as 10 m/h. However, th e removal of colloidal COD remained poor under all experimental conditions. The treatment of raw sewage and paper-filtered sewage in a fed-batch recir culation system under anaerobic conditions resulted in average removal effi ciencies for colloidal COD of 63% and 81%, respectively at a temperature of 24 +/- 1 degrees C. Therefore, the presence of an anaerobic biofilm and th e removal of suspended solids (SS) from the influent increased the removal efficiency of colloidal COD in the treatment of domestic sewage in an anaer obic polyurethane-foam filter. (C) 1999 Elsevier Science Ltd. All rights re served.