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%).