UBC Undergraduate Research

An Assessment of the Greywater and Composting Toilet Tea Leach Field Geochemistry at the C.K. Choi Building, University of British Columbia Vancouver Campus Larson, Leila


The geochemistry of a wetland system around the C.K. Choi Building on the University of British Columbia’s Vancouver Campus was assessed. The wetland system accepts compost tea from 5 composting toilets in the building as well as greywater from the building sinks. The system was estimated to receive approximately 400L/day and has an area of 30m2 and a depth of approximately 1m. Dilution and geochemical processes reduce the concentrations of trace metals and nutrients in the inflowing greywater and compost tea. Removal efficiencies of 99% for ammonia were observed in the system and are attributed to nitrification and dilution. Nitrate/nitrite sees removal efficiencies of 98%, due to denitrification and dilution. Manganese(IV) and Iron(III) reduction is observed to produce soluble Mn(II) and Fe(II) which are then easily adsorbed by phosphorus and precipitated as hydroxyapatite, MnHPO4, vivianite and strengite.Sulfate reduction also takes place and facilitates the precipitation of metal sulfides such as iron sulfide.

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