Enhanced nutrients enrichment and removal from eutrophic water using a self-sustaining in situ photomicrobial nutrients recovery cell (PNRC)

Nutrients removal and recovery from surface water are attracting wide attention as nutrients contamination can cause eutrophication even threaten human health. In this study, a novel in-situ photomicrobial nutrient recovery cell (PNRC) was developed, which employed the self-generated electric field to drive nutrient ions to migrate and subsequent recovery as microalgae biomass. At an external resistance of 200 Ω, the current density of the PNRC reactor reached 2.0 A m⁻², more than 92% of ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃⁻-N), and total phosphorus (TP) were separated from eutrophic water, which represented <0.19 mg L⁻¹ of NH₄⁺-N, <0.23 mg L⁻¹ of NO₃⁻-N, <0.02 mg L⁻¹ of TP were left in the eutrophic water effluent. Meanwhile these separated NH₄⁺-N, NO₃⁻-N, and TP were highly enriched in the cathode and anode chambers, and further removed from the system with the removal efficiencies of 91.8%, 90.6%, and 94.4%. The analysis of microbial communities unraveled that high nitrate removal was attributed to the abundant denitrifying bacteria (Thauera, Paracoccus, Stappia, and Azoarcus). The removal of ammonia was attributed to the algae assimilation (69.3%) and nitrification process (22.5%), and the phosphorus removal was mainly attributed to C. vulgaris. The preliminary energy balance analysis indicated that the electricity generation and biodiesel production could achieve energy neutrality theoretically, further demonstrating the huge potential of the PNRC system in cost-effective nutrients recovery from eutrophic water.