Slow sand filtration for water and wastewater treatment – a review

Water pollution is a serious global issue. Various technologically advanced treatment methodologies, for example, activated sludge process, upflow anaerobic sludge blanket, membrane bioreactor, trickling filter, rotating biological contractor, oxidation ditch, are widely studied, well documented and adopted in practice. However, attention to promising low-investment-cost technologies, such as slow sand filtration (SSF) techniques, is surprisingly miniscule. SSF (at a flow rate of 0.1–0.2 m3/h) is quite effective water treatment technology. It is also efficient in removing coliform microorganisms such as Giardia, Cryptosporidium, Salmonella, Escherichia coli, total coliform (TC) and fecal coliform, fecal streptococci, bacteriophage, MS2 virus from water/wastewater. Apart from reduction of pathogenic load, which is ascribed to the biological processes, SSF can efficiently remove turbidity, suspended solids and toxic metals in treated water. The SSF treated effluent conforms to the discharge standards for potable (drinking) and/or non-potable (such as irrigation) uses. The paper reviews the basic mechanism, design criteria for achieving the best treatment efficiencies in SSF, along with its potential application areas. Further research is, however, needed to focus upon the composition and characteristics of schmutzdecke layer at molecular level.