Study On The Effect Of Peroxide Pretreatment On Anaerobic Digestion Of Sludge In Wastewater Treatment Plant

Anaerobic digestion technology can convert organic waste into clean energy methane,so it is popular in sewage treatment plant sludge treatment in recent years.However,the effect of sludge anaerobic digestion is not ideal due to the slow hydrolysis process.Peroxide pretreatment is expected to promote sludge hydrolysis and increase methanogenic yield.Notably,the application type,purity and dosage of peroxide and its effect on different types of sludge remain unclear.In view of this,this paper taked different sludges generated by A²/O process as the research objects,firstly selected the best peroxide,then studied the effect of the best peroxide pretreatment on primary sludge and waste activated sludge,and finally discussed the effect of the best peroxide pretreatment dose on waste activated sludge.The aim is to provide a new idea for efficient resource utilization and ecological security of sludge based on anaerobic digestion.The main results and conclusions are as follows:（1）After pretreated with 75%and 32%Ca O₂ and 32%Mg O₂for 72 h,the dewatered sludge dissolution rates of sludge were 5.35%,5.87%and 5.84%,respectively,indicating that the three kinds of peroxide can promote the dissolution of dewatered sludge.Ca O₂pretreatment with a purity of 32%had a greater impact on the properties of waste activated sludge compare with primary sludge.In addition,the Fecal Coliform removal rate of both sludges reached 100%after 72 h pretreatment.（2）Batch tests of mesophilic anaerobic digestion（MAD）and thermophilic anaerobic digestion（TAD）were performed on dewatered sludge pretreated with 75%and 32%Ca O₂ and 32%Mg O₂ for 72 h,respectively.The results showed that the maximum methanogenic potential（P₀）and maximum methanogenic rate(R_max)of 32%Ca O₂pretreatment group were the highest at medium temperature,which were 10.42%and86.60%higher than that of the control group,respectively.Under high temperature condition,only 75%Ca O₂ pretreatment could slightly promote sludge methane production.However,32%Mg O₂ pretreatment inhibited the methane production of MAD and TAD.The above pretreatment mainly affected the production of organic matter in the early stage of digestion and reduced the concentration of PO₄^3--P in the sludge supernatant,but it may also lead to the risk of ammonia inhibition in TAD.In addition,all pretreatment increased the total phosphorus content in biogas residue and decreased the chroma and phosphorus concentration in biogas slurry.Only 32%Ca O₂ and 32%Mg O₂ pretreatment could reduce heavy metals in biogas residue.（3）After pretreated with Ca O₂ of 32%purity and 0.33 g/g VS for 72 h,the increase of alkalinity and initial acetic acid concentration of waste activated sludge was greater than that of primary sludge.The P₀ and R_max of waste activated sludge MAD were increased by 40.52%and 58.43%,respectively,but the P₀ and R_max of primary sludge MAD increased by 11.23%and 6.02%,respectively.In addition,the average concentration of PO₄^3--P in supernatant of pretreated primary sludge and waste activated sludge MAD decreased by 78.76%and 76.72%,respectively,compared with the control groups.The heavy metal contents of biogas residue of both sludges decreased and nutrient contents increased,but the total nutrient content of waste activated sludge was higher than that of primary sludge.Finally,pretreatment also reduced the chroma and phosphorus concentration of both biogas slurries,and made the biodegradability of waste activated sludge biogas slurry worse.（4）After pretreated with different dosage of Ca O₂ with a purity of 32%for 72 h,the p H,total ammonia nitrogen（TAN）,dissolved chemical oxygen demand（SCOD）,dissolved protein and dissolved polysaccharide contents of waste activated sludge were increased with the increase of Ca O₂ dosage.Three-dimensional fluorescence analysis showed that Ca O₂ could effectively decompose humic acids at all the doses used in the experiment.When the dosage of Ca O₂ was greater than or equal to 0.33 g/g VS,the Fecal Coliform removal rate reached 100%after 72 h pretreatment.（5）When the Ca O₂ dose was 0.33 g/g VS with a purity of 32%,waste activated sludge MAD had the maximum methanogenic potential and the highest initial acetic acid concentration,and the alkalinity remained high throughout the MAD process.Meanwhile,the removal rate of PO₄^3--P in sludge supernatant increased with the increase of Ca O₂dosage.In addition,the high concentration of NO₃^--N in the pretreatment groups made the initial N₂ content in MAD higher than that in the control groups.With the decrease of NO₃^--N concentration and microbial activity in the system,N₂ content in the biogas of the pretreatment groups decreased on the 5th day of MAD.