Research On The Recovery And Utilization Of Excess Sludge Based On Enzymatic Hydrolysis Pretreatment

The development direction of wastewater treatment is the resource and energy utilization of wastewater.The excess sludge is rich in organic matter and nutrients such as nitrogen and phosphorus,and has great potential for recycling.The hydrolysis of extracellular polymer macromolecules and the process of microbial cell disruption are the rate-limiting steps for the recycling of excess sludge.In this study,the excess sludge was pretreated by enzymatic hydrolysis to promote rapid hydrolysis and cell cracking of organic particles,and significantly increased the rate and amount of phosphorus release.Phosphorus was recovered from the supernatant after enzymatic hydrolysis by struvite crystallization and vivianite crystallization method,and phosphorus crystals were obtained by solid-liquid separation.The residue is rich in organic matter such as humic acid,which is used to adsorb heavy metal ions after recovery.Research on the recovery and utilization of excess sludge based on enzymatic hydrolysis pretreatment,the excess sludge is recycled and utilized for phosphorus and carbon resources more thoroughly.The main research results are as follows:（1）The excess sludge was pretreated by enzymatic hydrolysis,and the effects of different enzyme types,temperature and addition amount on phosphorus release effect were combined,and the optimal enzymatic hydrolysis conditions were as follows:2%mixed enzyme was added,enzymatic hydrolysis was performed at 45°C and 150 r/min for 11 h,and the mass concentrations of PO₄^3-and NH₄⁺in the supernatant after enzymatic hydrolysis were 163.58mg/L and 140.21mg/L,and the molar ratio of N/P was 4.57.Phosphorus recovery by struvite crystallization,and the optimal crystallization conditions were as follows:p H 9.5,Mg/P molar ratio 1.6,reaction time 20 min,standing aging for 2 h.At this time,the recovery rates of P and N were 99.56%and 35.92%,respectively.（2）The excess sludge was flocculated by ferric chloride to obtain iron-rich phosphorus sludge,and the iron-rich phosphorus supernatant was obtained by enzymatic hydrolysis for 11h.At this time,the p H was 4.14,the mass concentration of PO₄^3-was 186.34 mg/L,the mass concentration of Fe²⁺was 242.18 mg/L,and the molar ratio of Fe/P was 2.21.The optimal crystallization conditions were as follows:first adjust the p H to 6,centrifuge at 4°C and 10000r/min for 10 min to recover crude protein,then adjust the p H to 7.5,and react for 2 h at 25°C,at which time the recovery rate of phosphorus was 99.62%and the purity of vivianite was97.44%.（3）Humic acid was extracted from the excess residue after crystallization,and the adsorption kinetics and isothermal adsorption test showed that the adsorption process of humic acid to Pb²⁺,Cr²⁺and Zn²⁺was divided into three stages:fast adsorption,slow adsorption and dynamic equilibrium,and the adsorption amounts during adsorption equilibrium were 6.98mg·g^-1,4.97 mg·g^-1 and 4.85 mg·g^-1,respectively.The quasi-secondary kinetic equation is more consistent with the humic acid adsorption process,and the Freundlich model is better than the Langmuir model.