Refractory dissolved organic matter as carbon source for advanced nitrogen removal from mature landfill leachate: A review and prospective application

Partial nitrification-anammox is a promising process in mature landfill leachate treatment, but there is 11% residue nitrate to be removed. Denitrification or partial denitrification process can be used to remove the nitrate in the presence of carbon source to achieve advanced nitrogen removal. However, there is a lack of biodegradable organic matter in mature landfill leachate which can be used as carbon source for denitrification. Fortunately, refractory dissolved organic matter has been exploited to be used as a potential carbon source for denitrification in recent years, which is expected to achieve advanced nitrogen removal in mature landfill leachate treatment. Bacteria such as Chloroflexi can biodegrade refractory dissolved organic matter in mature landfill leachate as readily biodegradable organic matter by sludge adsorption-degradation mechanism, which can promote advanced nitrogen removal in anammox-based process. Furthermore, in order to improve the refractory dissolved organic matter utilization efficiency, several methods to improve the biodegradability of refractory dissolved organic matter are summarized, which include extended hydraulic retention time, prolonged sludge retention time, bioaugmentation and advanced oxidation processes. A novel integrated anammox-based process is proposed for mature landfill leachate treatment, in which ozonated nanofiltration concentrate is recirculated to provide carbon source for advanced nitrogen removal. Compared with conventional treatment process, this proposed process has the advantage of both economical- and environmental-effective in mature landfill leachate treatment. [Display omitted] •The lack of denitrifying carbon source in mature landfill leachate is discussed.•The feasibility and mechanisms of rDOM as denitrifying carbon source are reviewed.•Methods to improve the biodegradability of rDOM are summarized.•A new process is proposed for advanced nitrogen removal with NFC recirculation.