Wastewater-leachate treatment by microalgae: Biomass, carbohydrate and lipid production

Increases in wastewater discharges and the generation of municipal solid wastes have resulted in deleterious effects on the environment, causing eutrophication and pollution of water bodies. It is therefore necessary to investigate sustainable bioremediation alternatives. Wastewater treatment using consortia of microalgae-bacteria is an attractive alternative because it allows the removal and recycling of nutrients, with the additional advantage of biomass production and its subsequent conversion into valuable by-products. The present study aims to integrate wastewater and landfill leachate treatment with the production of microalgal biomass, considering not only its valorization in terms of lipid and carbohydrate content but also the effect of nutrient limitation on biomass formation. The effect of treating a mixture of raw wastewater with different leachate ratios (0%, 7%, 10% and 15%) was investigated using a microalgae-bacteria consortium. Two microalgae (Desmodesmus spp. and Scenedesmus obliquus) were used. Nutrient removal, biomass concentration, carbohydrate, lipid and Fatty Acid Methyl Ester (FAMEs) content and morphological changes were evaluated. Removals of 82% of NH₄⁺ and 43% of orthophosphate from a wastewater-leachate mixture (containing 167 mg/L NH₄⁺ and 23 mg/L PO₄^3-) were achieved. The highest final yield was obtained using Desmodesmus spp. (1.95 ± 0.3 g/L). The microalgae were observed to accumulate high lipid (20%) and carbohydrate (41%) contents under nutrient limiting conditions. The concentration of Polyunsaturated Fatty Acids (PUFAs) also increased. Morphological changes including the disintegration of coenobia were observed. By using a mixture of wastewater-leachate it is possible to remove nutrients, since microalgae tolerate high ammonia concentrations, and simultaneously increase the algal biomass concentration containing precursors to allow biofuel production.