Bioconversion of mature landfill leachate into biohydrogen and volatile fatty acids via microalgal photosynthesis together with dark fermentation

Landfill leachate (LL) is endowed with double roles as refractory wastewater and nutrients/energy sources due to inherent vast inorganics and organics. Bioconversion of LL's nutrients into biohydrogen and volatile fatty acids (VFAs) via eco-friendly dark fermentation (DF) is a promising approach to simultaneously deal with environment deterioration and energy crisis, but its application is severely restricted by poor fermentative performance attributing to strong toxicity of LL and vulnerable vitality of fermentative bacteria. Herein, a novel conversion strategy was proposed by coupling microalgal photosynthesis with DF, which was capable of reclaiming nutrients and organics from LL to produce biohydrogen and VFAs relying on robust microalgae coupled with DF. Results demonstrated that microalgae grew well in 10% LL with maximum biomass concentration of 1.41 g/L. More importantly, 86.12% NH4+ and 53.00% organics were recovered from LL and stored as carbohydrates (26.4%), proteins (48.7%) and lipid (15.9%) in microalgal cells. The accumulated intracellular carbohydrate and protein were then converted into biohydrogen and VFAs via DF, producing 16.37 kJ/L of output energy with overall energy conversion efficiency of 11.76%. Transformations of macromolecular organics and possible conversion mechanism of microalgae biomass to bioenergy were detailed discussed. Together, this work may provide a promising strategy for better dealing with LL disposal.