Improvement of biosand filtration systems using silver-impregnated clay granules

Abstract Decentralized water treatment systems provide a viable cost-effective medium tolong term solution for the improvement of water quality under normal circumstances and particularly during a pandemic. Low-cost biosand filters (BSF) have been widely adopted in over 180 countries worldwide. However, they produce inconsistent flow rates and have a lower removal efficacy for Escherichia coli and turbidity during the first 4 weeks of use. Their improvement in terms of filtration rate, microbial and turbidity removal has been a new facet of this area of the study. A 3-month longitudinal study was conducted to evaluate the performance of a modified biosand filter (MBSF) in terms of flow rates in addition to removal of turbidity, and waterborne pathogens (E coli, Cryptosporidium parvum and Giardia lamblia) from drinking water by the addition of 5 cm silver embedded clay granules and a diffusion disk between the layers of sand. The mean physicochemical parameters of surface water used as feed for the filters were as follows: pH (7.1), temperature (28 °C), turbidity 112 nephelometric turbidity units (NTU), E. coli (log10 4.8 CFU/100 mL), C. parvum (11 oocysts/mL) and G. lamblia (32 cysts/mL). Results revealed a notable difference between the two filters in terms of turbidity removal; ranging between (51–92 %) and (98.6–98.8 %) for the BSF and MBSF, respectively. An addition of a diffusion plate between the layers resulted in an increased flow rate from 18.2 to 38.7 L/hour. The MBSF further demonstrated a higher removal efficiency of E. coli (99.8 %), C. parvum (100 %) and G. lamblia (100 %). Having successfully tested and improved a typical BSF to produce WHO compliant drinking water, this may serve as an appropriate decentralised treatment option for drinking water during the current pandemic and beyond; to meet sustainable development goals (SDGs).