Alternative Carbon Source Produced From Citric Acid Production Wastewater For Biological Treatment Of Wastewater

With the increasingly stringent wastewater discharge standards,the high cost of citric acid production wastewater?CAPW?treated by traditional anaerobic-aerobic biological process in standard has brought great economic and environmental burdens to enterprises.Based on the discharge characteristics of CAPW,the resource potential of citric acid production wastewater as an alternative carbon source for the biological treatment of domestic and industrial wastewater was evaluated.From the perspectives of economy and resource,a pilot-scale process was established successfully,which could effectively recover the nitrogen and phosphorus elements in CAPW and the residual high-concentration organics was used as composite alternative carbon source?CACS?.The development of the process have important significances for solving the CAPW pollution issue,improving the comprehensive utilization efficiency of resources,achieving the coordinated development of the industry's environment and economy,and promoting the upgrade of the entire wastewater treatment system.The performance of CACS as alternative carbon source for enhancing the treatment of domestic and industrial wastewater was comprehensively evaluated.The differences of using NaAc and CACS as co-metabolic substrates for enhancing the treatment of low-concentration polyether wastewater?LCPW?were comparatively analyzed,and the performance differences between NaAc and CACS were elucidated from the variations on extracellular polymeric substance?EPS?content,dehydrogenase activity?DHA?and microbial community structure.The effect of CACS and NaAc as alternative carbon source for enhancing the biological nutrients removal and their influences on the characteristics of activated sludge were also comparatively analyzed.The mechanisms were further elucidated from the aspects of specific denitrification rate,denitrification potential and microbial growth factors.The main research contents and conclusions were shown as follows.?1?Optimization of operation parameters on CACS produced by CAPWApproximately 83.5%of chemical oxygen demand?COD?contained in CAPW was removed in 5 h biochemical reactions,indicating that the organics in CAPW had a good bioavailability,and a potential to be used as an alternative carbon source for enhancing the domestic and industrial wastewater treatment.Polyaluminum chloride?PAC??20%,w/w;calculated as suspended solids?SS??was added in CAPW after adjusting the pH to 9.5 via calcium oxide suspension?CaO??30%,w/w?.After solid-liquid separation,the removal efficiencies of total phosphorus?TP?,total nitrogen?TN?and SS were up to 92.1%,16.1%and 96.1%,while the loss efficiencies of COD and carbohydrates were only 11.0%and 13.2%,respectively.The ratios of COD/TN,COD/TP and biochemical oxygen demand?BOD₅?/COD in CACS was improved from 64.2,116 and 0.53 into 71.8,1358 and 0.65,respectively.The organic components of CACS are mainly organic acids and carbohydrates.High proportions of nitrogen and phosphorus elements were removed,indicating that CaO and PAC showed a good synergistic effect in improving CACS quality.?2?Complex and single carbon sources as co-metabolic substrates for enhancing the treatment of LCPW and theirs mechanismEfficient treatment of LCPW was difficult to be achieved via the unacclimated activated sludge?CK-AC?.Both NaAc and CACS can be used as co-metabolic substrates to acclimated activated sludge for the standardized treatment of LCPW.During the acclimation period of activated sludge,adding NaAc showed more efficient COD removal effect than that of CACS?P<0.01?.The activated sludge acclimated by NaAc and CACS?namely NaAc-AC and CACS-AC?could directly treat LCPW to meet the standards.Meantime,the removal effect of COD in CACS-AC was higher than in NaAc-AC?P<0.01?.Three-dimensional fluorescence analysis indicated that the fluorescence intensity of tryptophan proteins,soluble organic compounds and humic acids in seed sludge,NaAc-AC,CACS-AC and CK-AC were gradually decreased.Compared with seed sludge,the extracellular polymeric substance?EPS?and dehydrogenase activity?DHA?in NaAc-AC,CACS-AC and CK-AC were all gradually decreased,in which the downtrend in NaAc-AC and CACS-AC was moderate,and they could maintain higher EPS content and DHA,whereas the EPS content and DHA in CK-AC were separately decreased by 3.10-folds and 22.3-folds.It was indicated that the co-metabolic substrates reduced the damage of toxic pollutants on the metabolic system of activated sludge,and promoted the adaptation and retention of functional microorganisms.High-throughput sequencing analysis revealed that the bacteria diversity in seed sludge,CACS-AC,NaAc-AC and CK-AC were decreased gradually.Function microorganisms of seed sludge related to biological nutrient removal?e.g.,Nitrosomonadaceae and Rhodocyclaceae?could be reserved with a higher proportion in NaAc-AC and CACS-AC.In contrast,some microorganisms involved in degradation of toxic and macromolecule pollutions showed significant differences.Phycisphaeraceae?10.3%?and Lentimicrobiaceae?14.3%?were enriched in CACS-AC and NaAc-AC,respectively.The higher microbial diversity in CACS-AC may be the reason why it showed the best LCPW treatment performance.?3?Construction and analysis of CACS production process on pilot-scaleCoupling with the utilization of the excessive low-quality heat source and the CACS production parameters,a process with economic and production feasibilities was developed on pilot-scale.The volume yield of CACS during the solid-liquid separation process was over95.0%.The quality of CACS could be further improved after concentration process,in which the ratios of COD/TN and BOD₅/COD of CACS were separately improved to 83.8±1.22 and0.78±0.02.The improvement of CACS quality was due to the hydrolysis of partial polysaccharides and the stripping of free ammonia under the higher temperature condition.Ca?35.94%?,O?32.36%?,P?8.79%?,Si?7.32%?and C?6.91%?were the top five elements in ash of the residual solid matter from CACS production process.Given that the supplementary materials and the reaction types during CACS production process,the main components of the solid matter could be inferred as calcium phosphate,calcium oxide,perlite and a minimal amount of organics.The solid matter had a potential to be used as acid soil conditioner.Compared with the traditional anaerobic-aerobic biological process,the economic benefits of the CACS production process was more significant,and the profit and profit rate were separately up to 7.6 yuan/ton and 20.2%,showing a good prospect of engineering application.?4?NaAc and CACS enhanced the biological nutrient removal of municipal wastewater and theirs mechanismBoth NaAc and CACS could be used as alternative carbon sources for enhancing biological nutrient removal.The performance of NaAc for enhancing nitrogen removal was more significant?P<0.05?,while the performance of CACS for enhancing phosphorus removal was more efficiently?P<0.05?.In contrast of NaAc,some Ca²⁺and Mg²⁺carried in CACS can bridge the points of negative charge.Hence,CACS showed the characteristics of increasing the particle size and decreasing the absolute value of Zeta potential for activated sludge.The mean volume particle size and the absolute value of Zeta potential of activated sludge acclimated with CACS and NaAc were 54.46?m,41.06?m and 8.9±0.30 mV,12.6±0.33 mV,respectively.The gain effect brought by CACS may be that the divalent cations,such as Ca²⁺and Mg²⁺,can bridge the negative charge on the surface of activated sludge,and enhance the removal of phosphorus via chemical reaction.The denitrification process was fitted by the zero-order equation to characterize the denitrification efficiency of different organic components carried in CACS and NaAc.During the rapid degradation of carbon source,the specific denitrification rate of CACS was 10.0 mg-TN/?g-VSS·h?,which was 78%of NaAc.Based on the 95%removal rate of TN,the denitrification potential?P_D?and microbial growth factor?Y_D?of NaAc were 0.43 and 0.20g-TN/g-COD,which were separately 65%and 1.67-folds of CACS.Compared with NaAc,CACS could take into account both the maintenance of biomass and the supply of electron donors.Thus,long-term addition of CACS as an alternative carbon source of wastewater treatment system may have better application effects.