Highly efficient reverse osmosis concentrate remediation by microalgae for biolipid production assisted with electrooxidation

Phytoremediation of reverse osmosis concentrate (ROC) with microalgae can simultaneously achieve multi-functions of ROC treatment, CO2 mitigation and microalgae biolipid production. But the performances are usually inhibited by high free ammonia nitrogen (FAN) concentration and chromaticity of ROC. To offset these negative effects, an integrated technique including electrooxidation pretreatment and Chlorella vulgaris remediation was proposed, in which the ROC was first pretreated with electrooxidation to decrease FAN and chromaticity, and then the oxidized ROC was remediated with microalgae to reclaim nutrients and produce biolipid. Results showed that FAN was sharply reduced from 53.0 mg N/L to 13.9 mg N/L and chromaticity was decreased from 1600 to 100 Pt–Co via electrooxidation. Possible reaction mechanism of nutrients removal was discussed via electron mass balance. Explanation on chromaticity decrease was revealed by analyzing humic acid conversion path with fluorescence characteristics. During microalgae remediation process, nutrients removal rate, microalgae biomass concentration and lipid yield were effectively enhanced in electrooxidized ROC. Energy balance analysis indicated that microalge lipid energy under current density of 3.25 mA/cm2 basically compensated total input energy despite ROC sterilization. This work provided a promising strategy for large-scale ROC treatment and microalgae biolipid production. [Display omitted] •Free ammonia nitrogen and chromaticity was greatly reduced via electrooxidation.•Humic acid was degraded into family of soluble microbial by-products.•Precipitation of nitrogen and phosphorus occurred based on electron mass balance.•Microalgae growth and lipid synthesis were enhanced via electrooxidation.•Microalgae lipid energy almost compensated total input energy despite autoclaving.