Research On Process Of Municipal Wastewater Resourcelization With Enhancing Carbon Capture Efficiency And Energy Production

Municipal wastewater treatment usually uses the conventional activated sludge process(CAS)and its variant process to remove pollutants and achieve effluent quality compliance.However,wastewater itself is a valuable resource that contains high-value reclaimed water,nutrients and chemical energy.The traditional treatment method removed pollutants with high energy consumption,but failed to recover the corresponding resources.Therefore,wastewater resourcelization,which transforms wastewater treatment into wastewater resource recovery through the technology changes,is expected to become an important way to achieve sustainable development of water environment management.The main goal of wastewater resourcelization is to achieve the capture of organic carbon,the recovery of energy and the production of reclaimed water on the premise of the effluent quality reaching the standard.However,the existing process often has low carbon capture efficiency and poor energy production.Therefore,this paper carried out the research on the process of biosorption MBR combined with RO to enhance carbon capture,nutrient concentration,energy production and removal of nitrogen and phosphorus.Through investigating the performance of organic matter capture,concentrate capacity and removal of nitrogen and phosphorus,as well as analyzing the mechanism of carbon capture,sludge breaking and autotrophic denitrification,an efficient wastewater rcsourcclization system was established.The main research results were as follows:(1)A high-load membrane biorcactor(HL-MBR)and a novel high-rate contact stabilization membrane bioreactor(HRCS-MBR)were constructed.The results showed that with the increase of sludge retention time(SRT)(0.5-1.8 d),the effluent quality and biosorption performance of the two MBRs were gradually improved,and the cfficicncy of carbon capture were gradually reduced,while the membrane fouling was also relieved.Compared with HL-MBR,HRCS-MBR had a better biosorption performance under the same SRT condition.The inner and outer layers of the sludge were in an "empty stomach" state before entering the contact tank.After entering the contact tank,the extracellular polymeric substances(EPS)concentration rose rapidly and the sludge biosorption performance improved rapidly.At the SRT of 0.5 day,the carbon capture efficiency in HRCS-MBR achieved 56.9%.Membrane fouling analysis showed that the main components of the MBR membrane cake were protein and polysaccharide.HRCS-MBR had superiority over HL-MBR in membrane fouling control.Microbial community analysis showed the enrichment of Chloroflex was beneficial to the improvement of sludge flocculation performance.At the SRT of 1.2 days,the methane yield per unit concentrate of HRCS-MBR was 1073 mL·L-1,and the conversion of electric energy was 4.28×10-3 kW h.The above results proved that the novel HRCS-MBR was a highly effective and promising carbon capture process for municipal wastewater resourcelization.(2)Reverse Osmosis(RO)membrane was used to produce reclaimed water,and capture nutrients and residual organic matters from MBR effluent.HRCS-MBR-RO and UF-RO dual-membrane systems wereconstructed,respectively.The results of continuous operation showed that the quality of reclaimed water produced by the dual-membrane systems was good,and the concentration efficiency of the single RO membrane for total nitrogen(TN),total phosphorus(TP)and COD reached 71%,80%and 71%,respectively.Compared with MBR,the COD concentration in the effluent of direct UF membrane was higher,resulting in more serious membrane fouling of RO.For the same raw wastewater,the biochemical methane potential(BMP)of UF-RO concentrate was higher than that of MBR-RO,which indicated that UF-RO had advantages in organic matter recovery,but MBR-RO was more feasible in terms of membrane fouling control and energy consumption.(3)Through the combination of anaerobic digestion and anaerobic ammonia oxidation process,the organic matter removal,biogas recovery and autotrophic nitrogen removal of concentrated liquor were realized.A combined system of anaerobic membrane bioreactor(AnMBR)and completely autotrophic nitrogen removal membrane bioreactor(CANON MBR)were constructed.The results showed that AnMBR achieved rapid biological start-up within 37 days.CANON MBR that inoculated with Anammox after ammonia-oxidizing bacteria(AerAOB)enrichment achieved the nitrogen removal rate of over 78.2%within 27 days.The continuous operation test of the combined system showed that the methane yield was 223 mL·(g COD)-1,and the TN removal rate was 81.4%.Fluorescence in situ hybridization(FISH)analysis showed that AerAOB and Anammox coexisted in the sludge as dominant bacteria.(4)A composite CANON MBR system was constructed to enhance nitrogen removal and enrich Anammox using suspended media.The SEM results showed that the characteristics of the crater of Anammox biofilm on the inner wall of the media.A biofilter reactor with pyrite(BP)was constructed to strengthen the denitrification and realize the nitrogen and phosphorus removal of the concentrate.The TN and TP removal efficiency of 96.0%and 91.7%respectively were achieved in the combined CANON MBR and BP reactor,illustrating the advantages of the system.Illumina Miseq analysis showed that the family Brocadiaceae of typical Anammox was predominant in the biofilm of CANON MBR,while the family Nitrosomonadaceae of typical AerAOB had an advantage in suspended sludge.Thiobacillus and Sulfurimonas with autotrophic denitrification function were dominant in the BP reactor.According to the nitrogen removal performance and microbial community analysis,three nitrogen removal paths of the treatment system were determined and nitrogen removal mechanism clarified.(5)Pretreatment of HRCS-MBR sludge concentrate by combined Free Nitrous Acid(FNA)and Peroxymonosulfate(PMS)process was investigated.The batch experiment results showed that the dissolution of volatile solid.The batch experiment results showed that the dissolution of volatile solid COD increased by 0.158 mg·(mg VS)-1 while soluble Kjeldahl Nitrogen(SKN)and NH4+-N increased by 123.69 mg·L-1 and 64.42 mg·L-1,respectively compared with the raw sludge.The results showed that the coupling reaction could significantly enhance the sludge breaking efficiency and increase the dissolution of COD and N in cells.Continuous operation test showed that the combined treatment increased the dissolved COD,decreased the insoluble COD in the reactor,increased the hydrolysis rate of insoluble COD by 7.06%.and increased the methane yield by 36.69%.It proved that the combined treatment had a significant enhancement effect on the methane production of the system.Mechanisms analysis showed that PMS oxidized the sludge flocs,resulting in the breakup of insoluble cells in the flocs,which were diffused and transformed into the soluble organic matter.FNA could directly act on the cytomembrane and dissolve DNA,resulting in the breakdown and decomposition of sludge.(6)The continuous operation of wastewater resourcelization system showed that the RO membrane effluent met the quality requirements of irrigation water and industrial water from urban sewage reclamation in China,and the carbon capture efficicncy was stable at 53%-62%.After pretreatment of sludge and treatment of the concentrate,the average methane yield per concentrated liquid was 200.30 mL·(L Concentrate)-1,and the converted electric energy was 1.19 kW h.The removal rate of TN was 95.9%.The TP concentration was stable below 1.0 mg·L-1.The process technology route and material balance of the integrated process for wastewater resources recovery were set up.According to the calculation results of the experiment,the integrated process can achieve 74.7%of total water output,43.7%of total organic matters for methane energy recovery.70.8%of TN removal by complete autotrophic nitrogen removal process and 61.4%of P removal.Techno-economic analysis of the system showed that wastewater resourcelizationprocess can achieve partial energy self-sufficiency of 39.48%.After deducting the electrical energy consumption expense,the operation cost reduced to CNY 1.06 per ton of wastewater and actual profit of the integrated treatment project was CNY 1.42 per ton of wastewater,which achieved good economic benffits.