Removal of natural organic matter by an end-free gravity-driven membrane system combined with powdered activated carbon for household water supply

There is a considerable need for household water treatment (HWT) systems that can supply safe and affordable drinking water for low-and middle-income countries. One HWT system, an end-free gravity-driven membrane (GDM) system, has been developed to produce potable water. GDM systems can remove turbid material and pathogens but cannot reduce natural organic matter (NOM) effectively. Because chlorination has been widely used for HWT in low-and middle-income countries, there are chances of trihalomethane (THM) formation with NOM content in water. To reduce NOM, an end-free GDM system combined with powdered activated carbon (PAC) was adopted. The raw water used was groundwater and lake water spiked with a humic acid solution. For raw water with low NOM concentration, batch operation without PAC addition was preferable to prevent a significant decrease in permeability because of PAC cake layer formation. For high NOM concentrations, PAC addition was required to reduce dissolved organic carbon (DOC) concentrations and to keep total THM formation under acceptable levels, the concentration of which was theoretically calculated. In this case, to prevent permeability and pH decreases from PAC addition, sufficient PAC should be added into the raw water to maintain the PAC concentration as low as possible while still satisfying DOC removal requirements. The end-free GDM system combined with PAC would have significant potential for HWT in low-and middle-income countries.