Design of a Subsurface Waste Disposal System with Biological Denitrification

摘要

Nitrogen was removed from septic tank effluent in a nitrification-denitrification system, using greywater as the organic carbon source in the denitrification step. A preliminary study showed greywater from a typical home contained abundant soluble carbon that biodegraded at the same rate as methanol, which, until this study, appeared to be the most promising source of organic carbon for such a system. A second laboratory study used aerobic sand column reactors to nitrify unfiltered septic tank effluent, and fixed media columns consisting of stones. Greywater, settled sewage, and methanol were added prior to the denitrification step to determine their suitability as possible sources of organic carbon. A field demonstration model was then built, using an aerobic subsurface sand filter bed for blackwater nitrification and an anoxic denitrification reactor based on a five day liquid detention time. Some of the greywater from the household acted as the carbon source for denitrification, removing up to 99% of the available nitrate.