Study On The Influence Of Diversion Conditions On Sludge And Dissolved Organic Matter In Sidestream Enhanced Biological Phosphorus Removal Reactor

The sidestream enhanced biological phosphorus removal(Side-stream enhanced biological phosphorus removal,S2EBPR)process has stable biological phosphorus removal performance.The anaerobic fermentation of the side flow reactor can effectively reduce the dependence of traditional enhanced biological phosphorus removal(Enhanced biological phosphorus removal,EBPR)process on external carbon sources,and achieve the effect of functional microbial screening and sludge reduction through anaerobic fermentation of sludge.However,at present,there are few reports on the release of organic matter in the biological chemical process of the side flow reactor,as well as the characteristics of the system sludge and the changes of dissolved organic matter(Dissolved organic matter,DOM)under different diversion conditions.Therefore,this article uses the established S2EBPR process experimental platform to study the release patterns of soluble microbial products(Soluble microbial products,SMP)and extracellular polymers(Extracellular polymeric substances,EPS)under different anaerobic durations in the sidestream reactor.Based on this,the changes in sludge characteristics and DOM migration and transformation patterns of the S2EBPR process are analyzed,providing a theoretical basis for the development of sustainable low-carbon source wastewater treatment methods.The main research findings are as follows:(1)The appropriate anaerobic duration improves sludge dewatering and flocculation performance(relatively stable at 72～144 hours),and the sludge volume index(SVI)is basically stable at 107.6±0.7 mL/g at 0～72 hours.After 72 hours,microbial death leads to a significant increase in SVI and a decrease in sludge settling performance.The absolute value of the surface change of sludge showed no significant change between 72 and 144 hours,and reached its minimum value(7.75 mV)at 72 hours,at which point the electrostatic repulsion of sludge was the smallest.Anaerobic conditions have an impact on the morphology of sludge.Before anaerobic conditions,sludge microorganisms accumulate in multiple forms,and the cell surface is relatively smooth.After anaerobic conditions,there are obvious holes and depressions on the surface of sludge.The chemical components in SMP and layered EPS during different anaerobic periods are mainly protein and humic acid,but there are differences in material composition.SMP is mainly humic acid,while layered EPS is mainly protein.The difference in anaerobic duration affects the form and content of nitrogen and phosphorus release.TN concentration increases with the increase of anaerobic duration(up to 17.79 mg/L),and the released nitrogen element is mainly composed of NH4+-N and dissolved organic nitrogen(Dissolved organic nitrogen,DON).The average concentration of TP in the mud water mixture is 116.6 ± 1.7 mg/L,and the released phosphorus is mainly composed of PO43--P,EPS-P,and Poly-P.The concentration of PO43--P in the supernatant gradually increases with anaerobic time,mainly due to the release of extracellular phosphorus(EPS-P)and the hydrolysis of Poly-P.Anaerobic screening reduces the diversity of microbial communities,and excessive anaerobic duration inhibits the activity of phosphorus accumulating bacteria(Phosphate-accumulating organisms,PAOs).(2)The changes in diversion ratio conditions and sidestream sludge retention time(SRTss)have an impact on the sludge characteristics and micro morphology of the sidestream reactor.With the increase of SRTss,the capillary water absorption time(Capillary suction time,CST)and particle size of sludge first decrease and then increase,achieving good dewatering performance within the range of 20%to 10%diversion ratio(SRTss=72～144 hours).The protein content of loosely bound EPS(Loosely bond extracellular polymeric substances,LB-EPS)in the S2EBPR reactor sludge is the highest(41.67±13.95%),while the humic acid content of tightly bound EPS(Tightly bound extracellular polymeric substances,TB-EPS)is the highest(41.67±5.19%).The increase in DNA content in sludge EPS may be related to the decrease in sludge dewatering performance.Proteins may promote the aggregation of activated sludge microorganisms,increase the volume and particle size of sludge,and change the flocculation and sedimentation performance.The fluorescent substances in sludge EPS are mainly composed of protein tryptophan like substances,soluble microbial byproducts,and humic acid like substances.The phosphorus form of sludge is composed of PO43--P,EPS-P,and intracellular polyphosphate(Poly-P),with EPS-P mainly present in TB-EPS.The relative proportion of intracellular Poly-P in mainstream PAOs ranges from 51%to 76%,and the reactor has better phosphorus removal ability under 20%to 10%diversion ratio conditions(SRTss=72～144 hours).The increase in SRTss caused by the decrease in diversion ratio leads to the hydrolysis of Poly-P by sidestream PAOs,releasing more phosphorus.Changes in diversion conditions affect in situ sludge reduction in the S2EBPR process,with an apparent sludge yield(Yobs)of 0.26±0.03 g MLSS/g COD.The sludge reduction effect is equivalent to that of the aerobic sedimentation anaerobic(Oxic-settlinganaerobic,OS A)process,which is at least 25.7%higher than the traditional EBPR process listed in this study.(3)The chemical composition of the mainstream and sidestream DOM in the S2EBPR reactor is similar to that of the sludge EPS,mainly composed of humic acid,protein,polysaccharide,DNA,and contains a small amount of lipids.The total amount of DOM chemicals is approximately 14.26±3.01 mg/g VSS,and the decrease in diversion ratio conditions(increase in SRTss)accelerates the utilization of sidestream proteins,polysaccharides,and other substances,accompanied by the synthesis of humic acids.DOM fluorescent substances are composed of fulvic acid,humic acid,and protein like substances.The proportion of fluorescence intensity of sidestream humic acid and fulvic acid substances increases with the decrease of diversion ratio,and protein like substances continue to decompose,indicating that microbial hydrolysis and utilization of organic substances such as proteins is one of the internal reasons for the higher degree of side flow humification than the mainstream.The newborn DOM comes from mixed sources and is mainly endogenous.The nitrogen forms in the DOM of the S2EBPR system are mainly NO3--N and DON,which account for about 86.7%of the TN.The TN concentration in the sidestream reactor shows a trend of first decreasing and then increasing with the increase of SRTss.Under the condition of 20%diversion ratio(SRTss=72 hours),the concentration of TN in the sidestream is the smallest,only 7.83 mg/L.Under the range of 20%to 10%diversion ratio conditions(SRTss=72～144 hours),the proportion of effluent DON and effluent TN content were lower than other conditions,ranging from 6～13%and 12.18～13.91 mg/L,respectively.At this time,the denitrification performance of the reactor was relatively stable.The correlation analysis results of DOM indicate that a decrease in DOC content is accompanied by an intensification of DOM humification,an increase in mainstream DOM chemical substance content is accompanied by an increase in phosphorus element content,and an increase in chromophoric dissolved organic matter(Chromophoric dissolved organic matter,CDOM)content is mainly related to the increase and accumulation of humic acid and fulvic acid in the reactor.