Improving reverse osmosis concentrate treatment and nutrients conversion to Chlorella vulgaris bioenergy assisted with granular activated carbon

Landfill leachate (LL), especially the reverse osmosis concentrate (ROC), is a societal burden due to high toxicity but may have intrinsic values attributing to copious nutrients and organics. ROC bioremediation by microalgae has attracted much attentions benefiting from its extra advantage of bioenergy production. However, efficient microalgae cultivation with ROC is still a challenging task attributing to notorious ROC characteristics, like high chromaticity and toxicity. To alleviate these negative influences, a technique integrating granular activated carbon (GAC) pretreatment and microalgae bioremediation was proposed, with which nitrogen and phosphorus removal efficiencies achieved 100% along with an optimized microalgal biomass concentration of 1.44 g/L and lipid yield of 482.4 mg/L. Furthermore, a total volumetric energy yield of 33.6 kJ/L was acquired, which was conducive to realize energy valorization. The visualization evidence of three-dimensional fluorescence spectroscopy revealed chromaticity degradation mechanism of ROC as humic acids reduction and transfer to family of soluble microbial by-products. Meanwhile, contributions of GAC adsorption and microalgae assimilation on nutrients removal were analyzed. Together, this work provides a promising method and valuable information for ROC bioremediation with microalgae.