Algal purification of pretreated landfill Leachate

The efficiency of microalgae in removing various pollutants in landfill leachate after pretreatment by free stripping or air stripping was tested by a laboratory batch system. The results showed that Chlorella pyrenoidosa and Scenedesmus sp. had similar removal efficiencies with regard to ammoniacal‐nitrogen, oxidized‐nitrogen, orthophosphate and chemical oxygen demand (COD). The COD removal by algal treatment was better in Junk Bay (JB) leachate than in Gin Drinkers’ Bay (GDB) leachate (14–21% and 0.4–7% respectively). No significant difference (P > 0.05) was found in removing other nutrients including ammoniacal‐nitrogen, oxidized‐nitrogen and orthophosphate between leachate from the two landfills, regardless of the pretreatment used. The removal efficiencies of ammoniacal‐nitrogen and phosphorus were found to be higher in air‐stripped leachate than in free‐stripped one. Removal of ammoniacal‐nitrogen and phosphorus in air‐stripped leachate was 30% and 87% respectively. Poor removal of ammoniacal‐nitrogen was probably due to a deficiency in phosphorus (high N : P ratio) for algal growth in leachate. The two‐stage leachate treatment (ammonia stripping followed by algal purification) resulted in overall reduction of COD (38–51%), ammoniacal‐nitrogen (72–96%) and orthophosphate (79–96%).