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More than a billion people in the developing world lack access to safe and reliable sources of drinking water. Point of use (POU) household water treatment technology allows people to improve the quality of their water by treating it in the home. One emerging POU technology is the biosand filter (BSF), a household-scale, intermittently operated slow sand filter. Laboratory and field studies examined Escherichia coli reductions achieved by the BSF. During two laboratory studies, mean E. coli reductions were 94% and they improved over the period of filter use, reaching a maximum of 99%. Field analysis conducted on 55 household filters near Bonao, Dominican Republic averaged E. coli reductions of 93%. E. coli reductions by the BSF in laboratory and field studies were less than those typically observed for traditional slow sand filters (SSFs), although as for SSFs microbial reductions improved over the period of filter use. Further study is needed to determine the factors contributing to microbial reductions in BSFs and why reductions are lower than those of conventional SSFs.

Hydrophilic NOM caused little permeate flux decline and was poorly rejected compared with hydrophobic NOM. The influence of natural organic matter (NOM) composition on the rejection of total organic carbon (TOC), permeate water flux, and the strength and amount of NOM association with the membrane was examined in bench‐scale nanofiltration studies. NOM composition was manipulated by fractionation into hydrophilic and hydrophobic components and by powdered activated carbon (PAC) pretreatment with subsequent dilution to control for TOC concentration. Hollow‐fiber nanofilters made of negatively charged polysulfone were used in a batch recycle system. Hydrophobic NOM was shown to be responsible for nearly all permeate flux decline and was more highly rejected by the membrane than hydrophilic NOM. Using membrane‐feed solutions with the same TOC concentration, the authors found that the NOM remaining in solution after PAC pretreatment caused greater permeate flux decline and was more poorly rejected than the original mixture of NOM. NOM recovered from the membrane after nanofiltration was predominantly high‐molecular‐weight material (i.e., > 30,000 daltons).

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