Study On Sludge Reduction And Sewage Treatment Effect In Combined Systems Of ZVI+Cp Sludge Lysis And SBR Bioreactor

With the rapid development of national economy and the continuous improvement of people's living standard,a large amount of domestic and industrial sewage brings pressure to the environment.Activated sludge process,as the main method of sewage treatment at this stage,produces a large amount of activated sludge with huge volume and high moisture content.Its treatment and disposal has become a huge challenge and burden for the development of sewage treatment industry.And effective sludge reduction technologies are imperative.Among many methods of sludge reduction,in-situ sludge reduction can decrease the sludge production and its secondary pollution from the source.Sludge lysis-cryptic growth method is a simple and potential research direction.Sludge lysis treatment is the key to improve sludge reduction efficiency in this process.At present,the pHysical methods used in sludge lysis are energy-intensive and expensive,while the chemical methods are slightly inefficient and may produce some toxic by-products.In this study,calcium peroxide?CaO₂?and zero valent iron?ZVI?was used as a chemical lysis combination reagent to disintegrate activated sludge,and combined with SBR wastewater treatment system to construct a lysis-cryptic growth sludge reduction system.The optimum conditions of cell lysis were optimized by batch experiments.The reaction mechanism was determined,and the release of nutrients and the variation of extracellular polymers?EPS?in the process were investigated.Then the cell lysate was used as substrates in the sewage treatment system.The sludge reduction and sewage treatment efficiency,sludge settleability and dewatering performance and microbial community of the system were investigated.The main conclusions are as follows:The optimum conditions of CaO₂-ZVI cell-lysis test were detected to be:0.3g CaO₂/g VSS,0.1g ZVI/g VSS,initial pH=4 and reaction time=8h.PH regulation could promote the dissolution of CaO₂ and release of ferrous ion from ZVI.Then more OH·produced.Under the combined effect of strong oxidation of OH·and alkalinity,the cell lysis rate of sludge improved significantly,whichreached 19.5%?calculated by SCOD concentration?.Compared with the experiments with CaO₂only,the effect under optimum condition improved 52%,and was significantly superior to the traditional Fenton process.692.67 mg/L soluble protein,175.73mg/L soluble polysaccharide and 110.84 mg/L NH₄⁺released during the process.In addition,due to the immobilization of calcium and iron ions,PO₄^3-content was greatly reduced which was helpful to improve the phosphorus removal rate.At the same time,the structure of EPS was destroyed.Soluble EPS and LB-EPS increased significantly,and TB-EPS concentration decreased.By setting different reflux ratios,sludge lysis units and SBR bioreactors were combined to achieve cryptic growth.When reflux ratio was 0.7,excess sludge production?observation yield?and apparent sludge yield?real yield?were reduced by 59.64%and 28.3%,respectively.Excellent sludge reduction effect could be achieved.Meanwhile,it showed obvious regularity in community structure change in sludge reduction systems.Hydrolyzing bacteria?Saccharibacteria_genera_incertae_sedis,Ferruginibacter?and acidifying bacteria?Terrimonas?were effectively enriched to promote the utilization of granular carbon sources in the reflux lysate.Meanwhile,some chronic growth bacteria?Dechloromonas,Thauera?were enriched in the system.The mechanism of sludge reduction was well explained through the common role played by these bacteria from microorganism perspective.The cryptic growth-sludge reduction system also had better sewage treatment effect:the effluent COD concentration was slightly higher,which also met the first grade-A standards;the concentration of ammonia nitrogen was basically unchanged;the removal rates of total nitrogen and phosphate were strengthened and soluble microbial by-products?SMP?concentration in effluent have decreased.The sludge reduction system did not affect sludge settling performance and enhanced the excess sludge dewatering ability.