Household greywater treatment in water-stressed regions in cold climates using an ‘Ice-Block Unit’: Perspective from the coldest capital in the world

Abstract This note from the field shows a novel, hybrid concept of a constructed wetland for the first time in a water-stressed region in the coldest capital in the world, Ulaanbaatar, Mongolia. After selecting a suitable household compound, an ‘Ice-Block Unit’ was designed and constructed to assess its technical performance and capacity to reduce greywater-borne hazards during 2013 and 2014. This system was based on storing water during the winter freezing period as an ice block, and then starting treatment during the summer/non-freezing period. Results showed that the maximum removal rates of chemical oxygen demand (COD), NH 4 + , NO 2 − , total suspended solids (TSS), PO 4 − , and Escherichia coli were up to 100%, 99%, 97%, 97%, 87%, and 98%, respectively. The effluent met the neighbouring country, China's, municipal discharge standard of A grade effluent and could also be considered restricted and unrestricted irrigation water as reported in other studies. The system has proven potential from a technical point of view and can be scaled up to community or cluster levels. This would enable reduction of greywater-borne hazards in low, middle and high income countries with similar contexts.