The role of clogging in intermittent sand filter (ISF) performance in treating rural wastewater retention pond effluent

Abstract

Although biofilm growth caused clogging is often considered detrimental to the performance of intermittent sand filters (ISF), the presence of biofilm in ISF is indispensable for wastewater treatment. In this study, the role of biofilm growth clogging in ISF performance is studied by pilot experiments and biokinetic simulation. Both the pilot experiments and the simulation demonstrate that biofilm growth is significantly enhanced in the top layers of ISF and is dominantly comprised of heterotrophs. The clogging development zone was responsible for the majority of organic carbon and NH4+−N removal. Simultaneous nitrification and denitrification (SND) also occurred in the clogging development zone. The development of clogging can also enhance the organic carbon and NH4+−N removals as well as SND. Monte Carlo analysis indicated the lifetime of an ISF is negatively related to influent strength and hydraulic loading rate (HLR), and is more sensitive to influent strength than HLR. Although biofilm clogging is impacted by wastewater strength, HLR increase can send more biological removal burdens to layers below the clogging development zone, and thus negatively impact effluent quality due to reduced hydraulic retention time (HRT) within the ISF. Conservatively managed HLRscan reduce clogging development and limit biological removal burdens within the clogging development zone due to increased HRT. This study highlights the merit of managed biofilm growth in ISF and calls for research on advanced strategies to balance the positive and negative aspects of biofilm growth clogging in ISFs.