Study On Optimization Of Key Impactors For Alkaline-thermal Hydrolysis Of Excess Sludge

Activated sludge method was a widely used sewage biological treatment method,which was accompanied by the generation of excess sludge.With the urban construction and industrial development,the amount of sewage was increasing year by year,and the output of excess sludge was also increasing.In the context of global carbon cycle and carbon neutrality,the country no longer regarded excess sludge as waste,and attached great importance to the recycling of valuable resources in excess sludge.Excess sludge contained a large amount of organic matter,mainly protein,polysaccharide and oil,of which protein accounted for about30% ～ 60%.The protein was separated and extracted from the excess sludge,and it is used as the production raw material of foaming agent,soil conditioner,etc.It can realized the harmlessness of excess sludge and realized its resource utilization,which had good practical value.This study takes the surplus sludge of a sewage treatment plant in Shanxi as the treatment object,uses the alkali heat combined hydrolysis technology to extract the sludge protein,studies the Cao addition strategy dissolved by the extracellular polymer(EPS)of the surplus sludge,and optimizes the process conditions for extracting the protein from the surplus sludge from different sources.On this basis,the influence of the extracellular polysaccharide and oil content in the surplus sludge on the alkali heat hydrolysis effect of the surplus sludge is studied.The main research contents and results are as follows:(1)Research on Ca O addition strategy based on the dissolution of extracellular polymers from excess sludge.Ca O addition time,reaction time and Ca O addition amount all affected the EPS dissolution of excess sludge,while the Ca O addition method had no significant effect on EPS dissolution.At the beginning of the reaction,adding 20% powdered Ca O and reacting at80 °C for 50 min,the dissolution effect of EPS from the excess sludge is better.At this time,the concentrations of soluble protein and polysaccharide in the hydrolysate were 1263.89 and644.80 mg/L respectively,and the content of EPS in the hydrolysate was 2.89 mg / g TS.(2)Research on the optimization of protein extraction process by alkaline thermal hydrolysis of excess sludge from different sources.Four types of residual sludge from different sources were subjected to alkaline thermal hydrolysis under the same conditions,and the protein extraction rate and the solid-liquid separation performance of the hydrolyzed liquid were quite different,which was mainly due to the composition,content and spatial location of the organic matter in the excess sludge.of.Comprehensively considering the protein extraction effect and solid-liquid separation performance of the four types of excess sludge,when the addition of Ca O is 20%,the reaction temperature is 130 °C and the reaction time is 90 min,the protein extraction rate and solid-liquid separation performance of the four types of excess sludge are better.At this time,the protein extraction rates of excess sludge A-D were 33.08%,45.49%,23.65% and 46.06%,respectively.(3)Study on the effect of extracellular polysaccharide content on alkali-thermal hydrolysis of excess sludge.The increase of exopolysaccharide content has obvious inhibitory effect on the protein effect of excess sludge,and is not conducive to the solid-liquid separation of hydrolyzate.When the exopolysaccharide content was 350 mg/g TS,the extraction rate of protein was 29.62%,the DNA content in the hydrolyzed residue was 233.33 mg/g TS,the filtrate volume was 23.60 m L,and the viscosity of the hydrolyzed solution was 545.33 mp s.Three dimensional fluorescence spectrum and confocal scanning microscope observation showed that with the increase of extracellular polysaccharide content,the Maillard reaction between polysaccharide and protein increased,and the area coverage of polysaccharide increased,which were not conducive to the extraction of protein from excess sludge.(4)Study on the effect of oil content on alkaline thermal hydrolysis of excess sludge.The increase of oil content has an inhibitory effect on the extraction of protein by alkaline thermal hydrolysis of excess sludge,and the solid-liquid separation performance of the hydrolyzate deteriorates.Compared with the blank control group,when the oil content increased to 100mg/g TS,the protein extraction rate was 35.55%,the DNA content in the hydrolysis residue was283.10 mg/g TS,the filtrate volume was 27.75 m L,and the viscosity of the hydrolysis solution was 379.00 mp·s.The increase in the oil content of the excess sludge hinders the hydrolysis and lysis of the excess sludge,which in turn leads to a decrease in the extraction rate of protein and the deterioration of the solid-liquid separation performance of the hydrolyzate.