Growth and nutrient uptake of site-adapted microalgae in undiluted, high-strength landfill leachates

Abstract This study evaluated a site-adapted microalgae-bacteria consortium collected from a landfill in Lindlar, Germany. Growth performance of microalgae and overall nutrient dynamics were investigated in four undiluted landfill leachates from three German landfill sites, with ammonium nitrogen concentrations of 244–934 mg L⁻ 1 , chemical oxygen demand of 502–2076 mg L⁻ 1 and phosphate phosphorous of 1.42–6.94 mg L⁻ 1 . The microalgae achieved maximum growth rates of 0.37–1.20 g L⁻ 1 day⁻ 1 and final biomass yields of 3.0–5.1 g L⁻ 1 . Growth was mainly limited by phosphate-availability, often depleted by day 8, rather than by high ammonium concentrations. Variation of pH revealed consistent microalgal growth at pH levels between 7 and 9, indicating tolerance to free ammonia concentrations of up to 176 mg L⁻ 1 as well. After 15 days, inoculated cultures showed significantly lower concentrations of phosphate, nitrite, and nitrate compared with uninoculated control cultures, while ammonium removal was not detectable, indicating a microalgal preference for oxidized nitrogen forms, generated by nitrifying bacteria. The ability of these site-adapted microalgae to thrive in undiluted, high-strength leachates without pretreatment and to tolerate extreme ammonia levels highlights their potential for integration into wastewater treatment processes to improve nutrient recovery and resource efficiency.