Enhanced Release Characteristics Of Carbon,Nitrogen And Phosphorus By Microwave Heat Treatment Of Excess Sludge

At present,the upgrading of wastewater treatment plants is imminent.For low-carbon sewage in some areas of China,TN is the main indicator that restricts the discharge of wastewater treatment standards.In order to meet increasingly stringent effluent standards,domestic sewage plants mostly use extra carbon sources to increase operating costs.The excess sludge is rich in“carbon source”.The recovery of carbon source in the sludge is the key to reducing the cost of sewage treatment in future sewage treatment plants.Organic substances such as proteins in intracellular and extracellular polymers?EPS?are difficult to release due to the inhibition of microbial cell walls or cell membranes in the sludge and the binding of sludge flocs.The microwave treatment of excess sludge and the promotion of the release and utilization of organic matter in sludge have been the research hotspots of scholars at home and abroad.However,the current research focuses on microwave treatment of low solid content?1%to 6%?sludge,high water content,large processing volume,and waste of microwave processing energy.The viscosity of the sludge increases after microwave heat treatment of high solid content sludge,and the organic matter in the sludge is cracked or adsorbed,the dewatering property of the sludge is deteriorated,and the solid liquid phase is difficult to be separated,resulting in a decrease in the effective dissolution amount of the organic matter.The inorganic components in the sludge are complex,and the microwave cracking solution is difficult to recycle directly.The release and transformation process of the matrix such as carbon,nitrogen and phosphorus in the microwave heat treatment sludge is not clear.This topic intends to use the elution technology to promote the separation of organic matter and solid phase in the microwave heat treatment sludge.It is expected to enhance the release of high solid content sludge matrix by microwave washing through panning,thereby improving the effective dissolution of organic matter in the solid content sludge.rate.The main research contents include:release characteristics and influencing factors of microwave heat treatment matrix of residual sludge,and enhanced release characteristics of sludge matrix in microwave heat treatment,and explore the practical application feasibility of the elution technology to enhance the release of high solid content sludge matrix by microwave heat treatment.The research on sludge carbonization provides theoretical basis.The results show that:?1?The single factor influence experiment of microwave shows that:the microwave power was 800W,and the maximum COD dissolution rate of sludge was23.43%.The ratio of C/N in the cracking solution is 13.54,the ratio of C/P is 44.39,the ratio of NH₃-N/TN is increased to 0.43,the ratio of PO₄^3--P/TP is increased to 0.59,and the microwave power is increased in the sludge.The hydrolysis of organic substances such as proteins and amino acids into NH3-N and the decomposition of polyphosphates and organic phosphorus into PO₄^3--P promotes.When the solid content of sludge is 6%,the maximum COD dissolution rate of sludge is 23.53%.When the solid content of sludge is gradually increased to 17%,the COD dissolution rate of sludge is gradually reduced to 9.1%.It can be seen that the microwave treatment of high solid content sludge,the low dissolution rate of sludge organic matter,and the microwave treatment of high solid content sludge have limitations.When the microwave time is 10 min,the COD dissolution rate in the cracking solution is 23.32%;The microwave treatment time is prolonged to the extent of sludge floc and microbial cell wall damage,and the dissolution rate of sludge organic matter is no longer significantly increased;The microwave treatment temperature and the dissolution rate of sludge COD can be well fitted into a straight line,and there is a positive correlation between them?R²=0.951?.The prolonged microwave treatment time had limited damage to sludge flocs and microbial cell walls,and the organic matter dissolution rate of sludge did not increase significantly.The optimum experimental conditions for microwave heat treatment of excess sludge are as follows:power 800W,solid content 6%,microwave time 10 min,COD dissolution rate 24.12%,C/N and C/P14.6 and 44.13 respectively.?2?When the sludge with high solid content is treated by water washing and microwave,the maximum COD dissolution rate in the sludge was 18.04%,and the COD dissolution rate was increased by 6.2%compared with that before the panning.When the sludge was washed with lye?0.10 mol/L NaOH solution?,the maximum COD dissolution rate in the sludge was 39.21%,and the dissolution rate of COD was increased by 25.31%.?3?By studying the effect of alkali concentration of eluent on sludge matrix release,it is found that when NaOH concentration exceeds 0.1 mol/L,the increase of COD dissolution is not significant.From the economic point of view,attention should be paid to controlling alkali concentration in the actual process of application so as to save costs.This study suggests that alkali concentration is 0.10 mol/L.?4?When the sludge is washed with alkali and water,the maximum dissolution rate of sludge is 39.21%.Compared with washing with alkali solution,the dissolution rate of COD does not increase significantly.From the point of view of practical application,the best combination method is alkali and water washing.When the solid content is between 13%and 15%,the ratio of organic matter in eluent can meet the demand of nitrogen and phosphorus removal,and it has the potential to be used as a carbon source for subsequent resource utilization.?5?By analyzing the relationship between COD dissolution rate and energy consum ption of MW,MW-washing and MW-alkali-washing,it is found that the energy consumption of microwave is nearly three times that of microwave-washing,which indicates that the method of washing increases the effective utilization rate of microwave energy.In addition,the problems of organic matter being wrapped and adsorbed after microwave heat treatment of high solid content sludge were solved by washing method,which promoted the release of organic matter in sludge and improved the effective dissolution rate of organic matter.