Decomposition and mineralization of aquatic humic substances (AHS) in treating landfill leachate using the Anammox process

Aquatic humic substance (AHS) in landfill leachate is resistant to biodegradation, especially in anaerobic habitats. However, we reported here for the first time that AHS was completely biodegraded with the anaerobic ammonium oxidation (Anammox) process. As a result of aromatic-ring cleavage and mineralization, carboxylic and aliphatic organics were significantly produced, the contents of chromophores such as quinoid and ketone were remarkably decreased to decolorize the leachate, and produced carbon dioxide along with increasing carbonate was clearly presented. Of the degraded AHS of 137 mg L−1, 51 mg L−1 was owed to the oxidation with sulfate of 76 mg L−1 as electron acceptor, and the rest to other metabolic mechanism. Isolation and identification of heterotrophic bacteria revealed a diversified consortium comprising four facultative anaerobic species, Bacillus sp., Paenibacillus sp., Bacteroides sp. and Staphylococcus sp., without sulfate-reducing bacteria detected. Their contribution to AHS biodegradation and sulfate reduction under the special conditions with high oxidization–reduction potential and insufficient electron acceptors has not been known yet. Further work is underway to investigate their properties and respective duties in the consortium.