Biodegradation of N-Methylpyrrolidone (NMP) with a rotating algae-bacterial biofilm system

N-Methyl-2-pyrrolidone (NMP) is widely used in the lithium battery manufacturing industry, and residual NMP is discharged with production wastewater. Traditional physicochemical methods for treating NMP-containing wastewater face challenges such as high energy consumption, complex operations, and environmental risks. Considering NMP as a nitrogenous heterocyclic compound, this research investigated the potential of an algal-bacterial symbiotic system for the effective treatment of NMP wastewater. In this treatment approach, NMP was used as the exclusive source of nitrogen and carbon in the wastewater. The results demonstrated that in sequential batch experiments with NMP concentrations of 1000 mg/L and 4000 mg/L, removal efficiencies of COD, TOC, and TN all exceeded 95 %. Ammonium nitrogen produced from NMP degradation was efficiently absorbed by the algae within the biofilm, ensuring that the treated effluent met the wastewater discharge standards of the lithium battery industry. In semi-continuous flow experiments, maintaining a HRT of 72 h resulted in average removal efficiency of COD, TOC, and TN for 1000 mg/L NMP wastewater at 70.9 ± 3.7 %, 92.4 ± 0.7 %, and 37.8 ± 8.9 %, respectively. Microbial community analysis revealed that the presence of NMP enhanced the species richness within the biofilm. Heterotrophs Chitinophagales，Phormidesmiales were the most abundant bacteria, likely contributing to TOC degradation, while autotrophs Phormidesmiales and Trebouxiophyceae, Chlorella, Chloroflexales, Chloronema potentially playing a role in ammonium nitrogen absorption and fixation. The presence of protists and micro-metazoans such as Amphileptus, Rhabditida and Phascolodon, within the biofilms demonstrates a more complete biological chain within the biofilms, which contributes to the removal of pollutants from the wastewater. These insights offer a novel biological treatment technology for the efficient management of lithium battery wastewater.