Study On Enhanced Anaerobic Degradation Of N-methylpyrrolidone By Electrical Stimulation

As an important chemical raw material,N-methylpyrrolidone（NMP）is widely used in the production of lithium batteries,the pharmaceutical industry,and the production of insulating materials.As a result,a large amount of NMP wastewater is released into the environment.Due to the biological toxicity of NMP,the traditional anaerobic biological treatment showed poor performance on the removal of NMP in wastewater.Thus,in order to reduce the environmental pollution,it is of great importance to develop an effective treatment method to remove NMP.In this study,an up-flow electricity-stimulated anaerobic system was designed for the enhanced biodegradation of NMP wastewater.Firstly,electrochemical system,anaerobic biological system and electricity-stimulated anaerobic system were set up and the NMP degradation performances of these systems were compared.Among the three systems,the electricity-stimulated anaerobic system showed the highest degradation efficiency on NMP,whose removal rate was even higher than the sum of the electrochemical system and anaerobic biological system.It indicated that electrochemistry and microorganisms probably had a synergistic effect during the degradation process of NMP.Secondly,the influence of key factors on the removal efficiency of NMP,including applied voltage,influent loading rate,electron donor dosage and nitrate concentration,was further studied.The removal efficiency of NMP was increased with the growth of applied voltage（0-0.4 V）and the amount of electron donors(400-800 mg·L^-1),while it decreased with the increase of NMP loading rate(6.06-12.12 mol·m^-3·d^-1)and nitrate concentration(0-150 mg·L^-1).Under the optimal reaction conditions(the applied voltage was 0.4 V,the influent NMP loading rate was 6.06 mol·m^-3·d^-1,the sodium acetate concentration was 800mg·L^-1,no nitrate),the removal efficiency of NMP and TOC in the electricity-stimulated anaerobic system was about 93%and 90%,respectively.The degradation products were analyzed by gas chromatography and liquid chromatography-mass spectrometry,and the anaerobic degradation pathway of NMP in the electricity-stimulated microbial system was speculated.According to the bacterial taxonomic analysis,it was found that electrical stimulation facilitated the growth of heterotrophic NMP-degrading bacterias（Rhizobium）,autotrophic NMP-degrading bacterias（Paracoccus and Pseudomonas）,electrochemically active specie（Pseudomonas）,ammonifiers（Rhizobium and Pseudomonas）,fermentative specie（Bacteroidetes）,homoacetogen（Proteiniclasticum）and methanogen（Methanosaeta）,which contributed to the enhanced degradation and mineralization of NMP.Based on the bacterial taxonomic analysis and the identified intermediates,a possible metabolic mechanism dominating the enhanced anaerobic biodegradation of NMP in the electricity-stimulated anaerobic system was proposed.