Domestic wastewater treatment by slow sand filtration: A pretreatment to ultrafiltration
Sachin Madhavrao Kanawade
The present study investigates the effects of biologically active slow sand filtration (SSF) as a pre-treatment process prior to a pressurized ultrafiltration (UF) on a pilot-scale. The investigations were conducted with secondary effluent of sewage treatment plant. A series of filtration experiments under various operating conditions were conducted to investigate the subsequent performance of the UF. Transmembrane pressure (TMP) development of the UF unit shows that SSF reduces the foulant concentration in treated wastewater and causes much slower TMP increase versus run time compared with no pre-treatment. Experiments under different operating conditions show that applied filtrating flux and backwash interval (BWI) influence the performance of UF process to a large extend. Under certain presented operating condition sustainable operation of UF is achievable. In a further approach fouling critical operating conditions at high permeate fluxes and long BWI were applied. Three kinds of chemicals were added into the backwash permeate to compare the effect of enhanced backwash. The results demonstrate that by using hydrogen peroxides (H2O2 20 mg/L) or sodium hypochlorite (active chlorine 8-10 mg/L) in backwash process, the TMP was efficiently controlled during long operation time. Sodium hydroxide (pH 12) was not suitable as backwash reagent because of serious inorganic scaling under the conditions of Berlin secondary effluents.