Treatment of diluted landfill leachate using a granular microalgae–bacteria consortium

Landfill leachate is a complex wastewater, characterized by high concentrations of organic matter, ammonia nitrogen and refractory compounds, requiring the development of efficient and sustainable treatment technologies. In this study, the performance of a granular microalgae-bacteria consortium was evaluated for the treatment of diluted landfill leachate under controlled phototrophic conditions. The consortium consisted of the microalgal species Chlorella sp., Lobochlamys segnis and Phormidium sp., combined with activated sludge-derived bacterial communities, and was cultivated in a laboratory-scale photobioreactor operated in sequencing batch mode using leachate diluted to 2% (v/v). The treatment process was evaluated by monitoring organic matter, nutrients, biomass development and color removal. The granular consortium achieved high organic matter removal efficiencies, with COD reductions ranging from 74÷88% and BOD5 removal reaching 95%. Ammonium removal increased progressively during operation, reaching 92%, while total phosphorus removal reached 72%. The absence of nitrite accumulation and the presence of nitrate suggested the occurrence of nitrification processes within the consortium. Chlorophyll a concentration increased from 8.05 to 24.43 mg L⁻¹, indicating increased photosynthetic activity and successful adaptation of the biomass to leaching of deposits. Macroscopic observations revealed a continuous growth of granules, with diameters increasing from approximately 0.4 cm to over 1 cm. Despite the efficient removal of organic matter and nutrients, color removal remained limited (16÷56%), highlighting the persistence of refractory humic substances. The results demonstrate that granular microalgae-bacteria biomass represents a promising and sustainable approach for treating landfill leachate, combining pollutant removal with biomass production and nutrient recovery potential.