The Release Of Internal Carbon Source Via Thermophilic Micro-aerobic Digestion Of Excess Sludge To Promote Biological Denitrification For Low Carbon Nitrogen Wastewater

The carbon source has an important influence on the release of phosphorus in the anaerobic stage,denitrification and denitrification and the metabolism of heterotrophic microorganisms in the biochemical treatment of wastewater.It is generally believed that the normal denitrification reaction can only be carried out when the C/N(carbon to nitrogen ratio)in the wastewater biochemical treatment system is not less than 2.86,and the C/P(carbon to phosphorus ratio)required for the phosphorus removal process must reach at least18-20.In the actual application of the project,when the influent C/N is lower than 3.4,a supplementary carbon source is required to improve the efficiency of biochemical treatment.When the carbon source of the sewage treatment plant is low,measures or approaches such as methanol and sodium acetate can be used to meet the carbon source demand of the wastewater treatment process,but it will increase the operating cost of the sewage plant and increase the output of sediment.Compared with the traditional anaerobic fermentation that releases the carbon source in the sludge,the reaction process is slow and the release rate of the carbon source is low.This study uses the thermophilic micro-aerobic digestion(TMAD)technology to release the carbon source in the sludge and put it into the high temperature digestion system.Magnesium salt is added and process parameters such as pH are adjusted at the same time to increase the ratio of C/N and C/P in the digested supernatant,and optimize the quality of carbon source in the sludge.The carbon source of the obtained sludge was supplemented to the SBR reactor,and the effect of biological nitrogen and phosphorus removal from the wastewater was verified by simulated wastewater and actual domestic sewage,which provided high temperature micro-aerobic digestion to release the internal carbon source of the sludge to enhance the biological treatment efficiency of low-carbon nitrogen wastewater.Technical support and theoretical guidance.The effects of pH conditions,dosage of magnesium salt and dosing method on the carbon source release process in the sludge were investigated in the continuous operation of the TMAD digestion system.The appropriate process conditions were obtained: the molar ratio of magnesium to phosphorus is 1.4,and the magnesium chloride reagent is added at one time.Adjust the pH of the digestion system to 9.0 every 24 hours.When the reactor was operated under optimized conditions,the C/N and C/P in the digestion system at the 144 th hour were 20.9 and 139.0,respectively.Three-dimensional fluorescence spectrum analysis showed that the organic matter in the supernatant after sludge digestion contained microbial by-products and proteins,and increasing the dosage of magnesium salt could promote the transformation of microbial by-products.Under alkaline conditions,the higher the pH value,the more easily the protein in the digestive system will be metabolized and degraded to low molecular matter,and the protein substance cannot be detected in the system with pH 10.0 in the late reaction period.XRD analysis confirmed that struvite,a precipitated substance in the digested sludge,fully reflects that the reduction of nitrogen and phosphorus content in the digested supernatant is closely related to the addition of magnesium salt.In semi-continuous operation,after magnesium salt is added to the digestion system,the ratio of short-chain fatty acids SCFAs to chemical oxygen demand SCOD in the digested supernatant is 34.8～37.5%;the released protein and polysaccharides are usually quickly degraded,and the protein in the digestive juice the ratios of polysaccharides and SCOD were 2.0% and 2.8%,respectively.The molecular weight test results of organic matter showed that the proportion of substances with MW<10 KDa and MW<1 KDa in the total organic matter in the digestion process was maintained at 65.0～84.0%.When the TMAD system reached stable digestion under semi-continuous operation conditions,the organic matter in the digestive juice was mainly Small molecule substances.The sludge is digested and treated with high temperature and micro-oxygen technology,and the released sludge carbon source is added to the low-carbon nitrogen wastewater biochemical treatment system.The appropriate conditions for the SBR process system are as follows: DO 3.0～4.5 mg/L,C/N 7.0,digestion supernatant dosing amount 15 mg/L.SBR process aerobic operation for 2.5 hours,anoxic reaction for 3 hours,precipitation for 0.5hours and then drainage,the entire operation cycle time is controlled to 6 hours.When the SBR process is running continuously,the contents of SCOD,TN,and TP in the effluent are all in line with the first-class discharge standard stipulated in the "Emission Standard for Pollutants for Urban Wastewater Treatment Plants".When the TMAD technology is used to develop the internal carbon source of sludge,the cost of supplementing the carbon source of the low-carbon nitrogen wastewater biochemical treatment system will be lower than that of directly adding carbon sources such as ethanol.The developed technology is also conducive to the reduction of sludge in sewage treatment plants.