Assessing the potential of microalgae for nutrients removal from a landfill leachate using an innovative tubular photobioreactor

Abstract

Leachates treatment relies on the adoption of a multi-barrier strategy, involving primary, secondary, and tertiary processes. Due to their ability to grow in a wide variety of environmental conditions, and their nutritional requirements, especially in terms of nitrogen and phosphorus, microalgae appear as a promising alternative for the tertiary treatment of landfill leachates. Despite these advantages, only a few studies have promoted landfill leachates treatment using microalgae, most of them emphasizing the need for effluent dilution in water to minimize the toxicity and high color/turbidity of these effluents. An option to avoid the use of freshwater for effluent dilution would be the development of novel photobioreactors (PBRs), able to improve light absorption and, hence, light utilization efficiency by microalgae. This study evaluated the potential of Chlorella vulgaris and Tetradesmus obliquus on nitrogen (in the forms of nitrate and nitrite) removal from a pre-treated landfill leachate. Preliminary experiments using different concentrations of the pre-treated leachate were carried out in 1-L flasks. These results have shown that microalgal growth and nitrogen removal were higher in more diluted conditions. After selection of the adequate effluent concentration, a tubular PBR coupled to an optical reflector was used for biomass production. This innovative PBR is known to improve light distribution along the tube perimeter, enhancing microalgal photosynthetic activity. In fact, a significant improvement in C. vulgaris biomass productivities and nitrogen species removal efficiencies was observed in this PBR, confirming its potential as an effective platform for microalgal biomass production and tertiary treatment of landfill leachates.