Biodegradation of N-methyl-2-pyrrolidone (NMP) in wastewater: A review of current knowledge and future perspectives

Abstract

N-methyl-2-pyrrolidone (NMP) is a widely-used industrial solvent with high polarity, excellent water-miscibility, and chemical stability. Its strong toxicity and teratogenicity bring environmental and health risks. Recently, numerous research papers focused on the removal (degradation, recovery, etc.) of NMP from NMP wastewater. However, no publicly available review was found. This review listed the industrial applications of NMP and the corresponding wastewater generation. Also, it comprehensively summarized and compared the main strategies used in NMP wastewater treatment, including physical-chemical separation and resource recovery, chemical degradation, and biological degradation. For high-strength NMP wastewater (≥ 10%), resource recovery strategy (physical-chemical separation methods, i.e. distillation, extraction, and pervaporation, etc.) was the preferential choice. For wastewater with relatively low concentrations of NMP, chemical/biological degradation methods were commonly used. With the advantages of low cost, less secondary-pollution, and high mineralization efficiency, biological degradation methods were further specifically discussed including (1) biological treatment process technologies, (2) isolation/enrichment of NMP-degradation strains/consortia and its bioaugmentation applications, and (3) microbial degradation pathway of NMP. Typically, the aerobic/anoxic/anaerobic degradation of NMP was systemically investigated, and NMP was frequently reported as a denitrification carbon source. Finally, research gaps need to be filled in the future to promote the development of NMP-biodegradation technologies, including aerobic granular sludge (AGS), heterotrophic nitrification-aerobic denitrification (HN-AD) bacteria, NMP degrading fungi, synthetic biology technology and microbiome engineering based on the identification of more genes and key intermediates. This review provided guidance in NMP wastewater treatment and boosted the application of novel technologies.