Study On Strengthening Anaerobic Methanogenesis Performance Of High Salinity Organic Wastewater

A large amount of high salinity organic wastewater（HSOW）was produced in many industrial sectors,such as food processing,pharmaceutical manufacturing and leather processing industry.Anaerobic technology is widely used for treating HSOW,because of the advantage of low cost,good economic benefit and resources recycling.However,high content of salt could cause inhibitory and toxic effect on anaerobic microorganisms,and result in a lower growth rate of anaerobic microorganisms,even lead to cell rupture or death.Then,the anaerobic methanogenesis process will be severely inhibited,and the methane production efficiency will be reduced.Therefore,it is of great necessity to find an efficient method for enhancing the anaerobic methanogenesis performance of HSOW.Based on this,the influence of salt content on the anaerobic methanogenesis performance of HSOW was firstly analyzed,which could provide basic information for strengthening the anaerobic methanogenesis performance of HSOW.Then,nano-magnetite was used to enhance the anaerobic methanogenesis performance of HSOW,and the related mechanism was analyzed.At the same time,the optimal addition dosage of nano-magnetite was obtained.After that,KCl was used as the osmo-protectant,and nano-magnetite was added to the anaerobic reactor at the same time,to further enhance the anaerobic methanogenesis performance of HSOW.The synergistic effect of simultaneous addition of nano-magnetite and KCl on anaerobic methanogenesis of HSOW and involved mechanism was clarified.Finally,the anaerobic reactor was used to treat the HSOW.The promotion effect of the simultaneous addition of nano-magnetite and KCl in the start-up and long-term operation performance of the anaerobic reactor was explored.It could provide a foundation for the practical application of this method.The main results are as follows:（1）The anaerobic digestion methanogenesis performance of HSOW was analyzed under different salt concentration（0-4%）.The results showed that,the anaerobic methanogenesis performance of wastewater decreased with the increase of salt concentration.Especially,when the salt concentration was above 3%,methane production significantly decreased,acid accumulation occurred in the reactor,a large amount of acetic acid,propionic acid and butyric acid remained in the effluent,and the anaerobic digestion process was inhibited.（2）Nano-magnetite was used to enhance the anaerobic methanogenesis performance of HSOW,and the involved mechanism was analyzed.The results showed that,when the addition dosage of nano-magnetite was 200 mg/L,the cumulative methane production was the highest,which increased by 11.06%compared with the control group that without nano-magnetite.Under this condition,the COD removal rate increased,the VFAs degradation was accelerated,and the anaerobic methanogenesis performance was enhanced.The addition of nano-magnetite enhanced the activities of dehydrogenase,acetate kinase and F_420.The oxidation reduction potential（ORP）of the anaerobic system was reduced,which provided a better reducing environment for growth of anaerobic mocroorganism.At the same time,the activity of electron transport system（ETS）was improved impling the improved electron transport rate.Extracellular polymer（EPS）secretion of anaerobic mocroorganism was enhanced.In addition,nano-magnetite addition with the dosage of 200 mg/L elevated the richness and diversity of microbial population.In particular,hydrogenotrophic methanogens Methanolinea and Proteobacteria which could degrade small molecules of organic matter into acetic acid were enriched in the anaerobic system supplemented with 200 mg/L of nano-magnetite,and as a result the hydrotrophic methanogenic process and acetic acid production were enhanced.（3）The anaerobic methanogenic performance of HSOW with the simultaneous addition of nano-magnetite and KCl was analyzed.The results showed that,when KCl（0.174%）and nano-magnetite（200 mg/L）were simultaneously added,the cumulative methane production was the highest,which was 124.85%higher than that of the control group,and the corresponding effluent COD was reduced.The addition of nano-magnetite and KCl had a synergistic effect on the anaerobic methane production performance of HSOW,accelerated the degradation of acetic acid,propionic acid and butyric acid in the anaerobic system,and promoted the activities ofα-glucoside hydrolase,dehydrogenase,acetic kinase and F₄₂₀.Under such conditions,the richness and diversity of microorganisms in the anaerobic digestion system of HSOW were elevated.The hydrogenotrophic methanogen Methanoregulacea took acetate as necessary growth substrate,and Syntrophobacteraceae could decompose propionic acid into acetic acid by oxidation.Methanoregulaceae and Syntrophobacteraceae were enriched in the anaerobic digestion system.These results indicated that the simultaneous addition of nano magnetite and KCl not only promoted the conversion of propionic acid,but also further enhanced hydrogenotrophic methanogenesis pathways.（4）Four group of reactors,that is G1（control）,G2（200 mg/L nano-magnetite）,G3（0.174%KCl）and G4（0.174%KCl+200 mg/L nano-magnetite）,were used to treat HSOW.The promotion effect of nano-magnetite and KCl on anaerobic reactor start-up and long-term operation performance was analyzed.The results showed that,the acclimation of microorganism in anaerobic sludge was promoted,and the rapid start-up of the anaerobic treatment reactor of HSOW was achieved when KCl and nano-magnetite were simultaneously added.After that,as the organic loading rate greadually alevated and potassium ion concentration greadually decreased,and the COD removal rate of G4 anaerobic reactor remained at about 70%.Under this condition,the acclimated anaerobic microorganism could maintain good anaerobic methanogenesis performance.In addition,metagenomic analysis showed that the addition of nano-magnetite and KCl enhanced both acetoclastic and hydrogenotrophic methanogenesis pathway,increased the abundance of genes related to signal transduction,and decreased the abundance of genes related to K⁺,Na⁺transport and EPS secretion.This indicated that the synergistic effect of KCl and nano-magnetite improved the efficiency of microbial energy metabolism and signal transduction,and strengthened the start-up performance of anaerobic reactor for treating HSOW.