The Mechanisms Investigation On Short Sludge Retention Time Enhancing Sewage Phosphorus Bological Removal And Phosphorus Fixation Enhancing Dewaterability Of The Anaerobically Digested Sludge

With the putting forward of the national’s strategy of“carbon neutrality”and the policy of sewage sesource,the technical reform that toward to upgrating the level of sewage resource has become a new development trend and requirement in the sewage treatment industry.The organic matters concentration of the sewage in our country is generally low,but the concentrations of mud and sand are inversely high,which restricts the development and application of sewage sludge resource treatment technologies seriously.Therefore,technical modifications to improve the organic content in waste activated sludge（WAS）and technical innovations of key node to accelerate the resource level upgrating should be cond ucted from the original of sewage treatment process.This study combined the characteristics of the Adsorption-degradation（A-B）process which was commonly employed in sewage resource recovery with the configuration of wastewater treatment plant that is currently in operation,suggesting that short sludge retention time（S-SRT）biological phosphorus removal be employed as the technological schoice of the A stage to achieve simutanious and effective removal of carbon and phosphorus,the operational effectiveness and mechanism for enhancing biological phosphorus removal in treating real domastic sewage are investigated.Secondly,the WAS anaerobic digestion is necessary for the A-B process to realize resource recovery,but it pruducts a large amount of anaerobically digested sludge（ADS）that is difficult to dewater.This study proposes a dewaterability enhancing strategy,which combines oxidation disintegration with natural flocculants to realize the transformation of soluble phosphorus from the supermatant to the solid phase simutaniously,isintended to provide assistance for the safe treatment of ADS as well as the resource utilization.The ultimate goal of this study is to develop a technical method for the resource utilization of sewage and sludge with the core of“Short sludge retention time biological phosphorus removal-sludge anaerobic digestion-phosphorus fixation enhanced dewatering”,which will accelerate the process of innovation at currently operating waste water treatment plant toward resource utilization.Two sequencing batch reactor（SBR）opareted in anaerobic/oxic（A/O）mode were constructed and named as SBR_S-SRTand SBR_control.During the SRT adjustment period,when the SRT of the SBR_S-SRT was reduced from 5 d to 3 d,there were no appreciable differences between it and the SBR_control（SRT=10 d）in terms of chemical oxygen demand（COD）and phosphorus removal efficienc y.With the shorting of the sludge retention time（SRT）of SBR_S-SRT,the yield of organic containted in WAS(Y_WAS-organic)increased consistently.Based on the comprehensive analysis,this study selected SRT of 3 d as the operating condition for the SBR_S-SRTsystem during the short sludge retention time operational period,the COD removal efficiency was equal to that of the control system(SBR_control,2.5 h for oxide phase).Additionally,the average removal efficiencies for PO₄^3--P and total phosphorus（TP）were 92.78%and 90.78%,respectively,while the control system’s removal efficiencies were just 57.52%and 63.02%.The poor NH₄⁺-N removal performance,with an average removal efficiency of 16.06%,revealed the severe nitrification inhibition of the SBR_S-SRT.The SBR_S-SRT system did,however,continued to maintain good sludge settlebility.Compared to the control system,the content of mixed liquor volatile suspended solid（MLVSS）was much higher.The Y_WAS-organicof the SBR_S-SRT was 27.40%higher than that of the control system.The semi-continuous anaerobic digestion test verified that the WAS from the SBR_S-SRThad a methanogenic efficiency of 2.26 times that of the control system.The results showed that the S-SRT biological phosphorus removal technique could increased the content and yield of organic matter in sludge while effectively removing organic carbon in sewage.It could also improve the WAS’s biodegradability.It confirmed that S-SRT niological phosphorsu removal was a potential strategy for accomplishing the A stage goals,simultaneously removing COD and phosphorus,and speeding the resource recovery of sewage.The SBR_S-SRT system’s SRT was shorted during the SRT adjustment period,which enhanced the growth of polyphosphate accumulating organisms（PAOs）and eliminated nitrifying bacteria.Thus,the competition for organic carbon in the anaerobic phase between the release of phosphorus and denitrification was successfully reduced.The predominant genera of PAOs were Tetrasphaera,Halomonas,Hydrogenophag and unclassified＿f＿＿Comamonadaceae et al in the sludge samples from the S-SRT operational period.The relative abundance of main genera belonged to PAOs in the sample group of SBR_S-SRT was higher than those of the control system,according to the significantce analysis of differences among sludge samples from different operation times.Additionally,Moreover,the anaerobic phosphorus release and aerobic phosphorue uptaken activities of the SBR_S-SRT system’s sludge were 2.08 and 2.84 times those of the control system,respectively.The SBR_S-SRT system’s sludge contains significantly more phosphorus in the fraction of non apatite inorganic phosphorus（NAIP）and in the extracellular polymeric substance（EPS-P）.The results verified that the nitrifer was wash out caused nitrification to be severely inhibited,which reduced the carbon competition between denitrification and the release of phosphorus,ensured the carbon source demond of PAOs,realized the enrichment of PAOs,encouraged the sludge’s phosphorus uptaken activities,and ultimately achieved the enhancement organic carbon and phosphorus removal efficiency in the domastic sewage through the combination of biological polyphosphorus uptaken and biosorption.Due to the interaction of significant free radical oxidation and alkalinity,sodium percarbonate（SPC）and calcium peroxide（Ca O₂）,oxidants of“solid hydrogen peroxide”,were able to disintegrate sludge efficiently.However,Ca O₂effectively fixed the phosphorus that was released during disintegration process efficiently in situ,and it can be employed as the oxidant and phosphorus fixation agent in the process of synchronous phosphorsu fixation and oxidation combined with chitosan to improved the ADS’s dewaterability.The optimal Ca O₂ and chitosan dosages,as determined bu this investigation,were 0.12 g/g TSS（Total suspended solid,TSS）and 0.02 g/g TSS,respectively.This resulted in a reduction of the moisture content of dewatered ADS sludge cake to 61.27%.Mg²⁺was the ideal phosphorus fixation agent in the asynchronous phosphorus fixation and oxidation process,and the determined optimal dosage ratio of Mg²⁺and supernatant-contented PO₄^3--P in stoichiometry was 1.2:1.Under the optimal conditions,the SPC and chitosan were added at dosages of 0.05 g/g TSS and 0.03 g/g TSS,respectively.This resulted in a moisture content of the dewatered ADS sludge cake of 67.16%and a sludge resistance filtration（SRF）of 2.79×10⁸ m/kg.The transfer efficiency of phosophorus from sewage to dewatered ADS sludge cake was shown by t he mass balance of phosphorus in the combined processe of asynchronous and synchronous with SBR_S-SRT to be 86.6%and 87.9%,respectively.The main mechanisms for the two methods to enhance the dewaterability of ADS are the synergistic effect among those processes which include the release of non-free water along with the dissolution of organic matter during the disintegration of ADS floc caused by oxidation,and the reaggregation of chitosan on dissolved organic matter and cracked ploc particles.The S-SRT SBR technique for enhancing phosphorus removal and the ADS dewaterability enhancing technologies developed in this study have significant promise for practical application and can help with the targe of recovery resources from sewage sludge.