Microalgal phycoremediation of landfill leachate /

Abstract

The aim of this project was to explore the use of microalgae in remediation of landfill leachate. The isolation of microalgae strains tolerant to a combination of high dissolved salts and ammonia concentrations (typical for landfill leachates) was undertaken. The experiments were set up with low temperature and light intensity which makes microalgae-based phycoremediation relevant to conditions in Ireland. The growth of several microalgal strains and the resultant nutrient depletion was evaluated in laboratory batch culture experiments. The Chlamydomonas sp. strain SW15aRL achieved the highest pollutant reduction whereby a decrease of 90.7% of ammonia-nitrogen within 24 days was observed in 10% raw leachate (~100 mg·l -1 NH4 + -N) supplemented with phosphate. Further assessment of growth and nutrient reduction of strain SW15aRL was carried out across a number of different leachate samples to determine the effects that variable leachate composition can have on the sustainable growth of microalgae, when using leachate as the sole source of nutrients. Dilutions were applied to obtain 30 to 220 mg·l -1 NH4 + -N concentrations. The strain SW15aRL was capable of growth in a variety of leachates but depended on the overall composition profile rather than just dilution. Phosphate addition appeared to be essential even though precipitation occurred in some instances. Both inhibitory and limiting factors were identified, highlighting that dilutions were needed to maintain the solubility of specific constituents and to keep the toxicity of others in check, yet the dilutions also reduced the concentrations of key nutrients and minerals. Finally, a toxicological evaluation showed microalgae treatment contributed to the reduction of pollutant levels and ecotoxicity. While the microalgae activity causes major macronutrient reduction, there are several other physicochemical processes which contribute to reduction such as precipitation and volatilisation while the contribution from coexisting bacterial communities is still poorly understood