Microalgal bioremediation of nitrogenous compounds in landfill leachate – The importance of micronutrient balance in the treatment of leachates of variable composition

Abstract

Landfill leachate is a type of wastewater which is challenging to treat. Phycoremediation has been proposed as an alternative biological treatment for removal of ammonia nitrogen. Several studies have shown microalgae based bioremediation to be possible with ammonia tolerant microalgal species, provided that an optimal dilution is used and the initial molecular N:P ratio is adjusted.The composition of landfill leachate varies between sites and throughout the year. The performance of selected microalgal strains and their susceptibility to variation in landfill leachate composition is poorly understood. This study compares the growth of Chlamydomonas sp. strain SW15aRL in a variety of leachate samples. The leachate samples are from different sites including leachate sampled on different occasions from the same site. These substrates were diluted to obtain ammonia nitrogen concentration within the range of 30 to 220 mg·l−1.Results showed that strain SW15aRL was capable of growth in a variety of leachates but was dependent on the overall composition profile of the landfill leachate rather than just its dilution. Growth was negatively affected in two of the leachates tested, due to metal toxicity and mineral bioavailability or deficiency. Phosphate addition was essential for growth in the landfill leachates even though precipitation occurred in some instances. Ammonia nitrogen decrease varied between 70% and 100% in the substrates where microalgae could successfully grow.This study indicates that due to their overall mineral profile some landfill leachates are more suited for microalgae based remediation than others. Furthermore, this study indicates that a better understanding of other physicochemical processes that take place concurrently during the growth of microalgae in landfill leachate and which contribute to overall nutrient reduction is required.