An experiment on simultaneous operation of nitrification and denitrification of municipal landfill leachate in a single reaction tank

Abstract

Leachate from municipal disposal landfill brings a significant load of ammonia in receiving waters. Since phosphorus and degradable organic carbon are mostly filtered out from the leachate in the course of subsurface runoff, conventional treatment technology such as activated sludge process is not available for nitrogen removal from the leachate. The authors are developing a new biological technology of low-cost leachate treatment which consists of nitrification with micro-bubble (MB) aeration and denitrification by using fatty acid compounds, FAC. Laboratory experiments showed that denitrification was in progress even in an aerobic reactor, when carriers coated with FAC were equipped in the aeration tank. The result indicates that both the nitrification and denitrification simultaneously occurred in a single reaction tank, which suggests there is the possibility to devise an economically feasible treatment system with a very simple structure. The biochemical nitrogen removal mechanism involved in the proposed system is considered to be like the following. First, the anoxic leachate was nitrified by the MB aeration and most of ammonia was oxidized into nitrate. Secondly, the nitrate was reduced and denitrified in an anoxic sub-layer of denitrifying bacteria biofilms that were formed on the surface of carriers. In the denitrification process, FAC contributes to denitrification in two ways. The first is to consume dissolved oxygen and to create anaerobic environment. The second is to nourish denitrifying bacteria as a hydrogen donor and carbon source. Such biochemical processes were experimentally investigated by analysing water quality balance. This study provides an insight into scientific background for labour and energy saving technology of leachate treatment.