Study On Fenton-like Conditioned Sludge For MEC Hydrogen Production And Phosphorus Recovery

Excess sludge is a by-product of the sewage treatment,and the sewage has large amount,high water content,and complex composition.Its main components are functional microorganisms and extracellular polymers?EPS?which are rich in organic matter,and the necessary growth elements,N,P,K,etc.The utilization of sludge resources has become a worldwide research hot topic.In this dissertation,the utilization of excess sludge has achieved in the following three aspects:first,the establishment of a neutral PCA?Protocatechuic acid?and Fe³⁺/H₂O₂ system for the conditioning of excess sludge,and the optimization of neutral PCA/Fe³⁺/H₂O₂ system operationparameters through single-factor tests and response surface methodology to achieve;secondly,excess sludge af-ter the neutral PCA/Fe³⁺/H₂O₂ treatment was further processed in an microbial electrolysis system?MES?;Thirdly,struvite was synthesized with both chemical systhesis and MEC supernatant to have phosphate recoved from excess sludge.The following conclusions were achieved:1.The contribution order of the final primary?Soluble chemical oxygen demand,SCOD?and secondary factor?Total phosphorus,TP?was H₂O₂ dosage>reaction time>n?PCA?:n(Fe³⁺)>Fe³⁺dosage by single factor test extreme results.The results of sin-gle-factor tests showed that the best condition of PCA/Fe³⁺/H₂O₂ system for conditioning excess sludge effected by each independent factor were:the reaction time was 120 min,n?PCA?:n(Fe³⁺)=1.5:1,the dosages of Fe³⁺and H₂O₂ were 12 mmol/L and 0.4 mol/L,re-spectively.The results of the RSM optimal condition analysis showed that the optimal value of Fe³⁺dosage and H₂O₂ dosage on the excess sludge was 12.4 mmol/L and 0.45mol/L.The R² of the excess sludge TP content in the liquid phase and the SCOD were0.9062 and 0.8431,respectively.In the regression equation,and the quadratic equation model was significant.Under the optimized conditions,the actual values of TP and SCOD in the liquid phase of the remaining sludge were 60.14±0.08 mg/L and 3337.67±66.37mg/L,respectively.The actual and predicted RSD were 1.79%and 5.19%,respectively,which indicates that the RSM optimization results are highly reliable.2.The effect of sludge condition on sludge disintegration was analyzed from the aspects of sludge particle size,changes of EPS organic components,and the microstructure of sludge.The volume mean diameter of the conditioned sludge was reduced by 22.78%,and the specific surface area was increased by 58.94%,confimed the sludge flocs were disintegrated into smaller sizes,the soluble polysaccharide and soluble protein in the extracellular polymer released to the supernatant to a certain extent,which induced the SCOD content in the supernatant increased by more than 5 fold.Through the operation of MEC,the effect of the condition process on the performance of MEC was analyzed.The TCOD removal rate of conditioned sludge was increased by 30.03%.However,the removal rate of polysaccharide was increased by 50.16%,the removal rate of protein was increased by 97.31%,and the utilization rate of organic acids for the sludge increased in MEC,and the propionic acid content in the condition sludge was significantly less,only45.57%of the original sludge.The total isobutyric acid and butyric acid content in the conditioning sludge were 83.57%of the original sludge.In terms of electrochemical indicators of MEC,after the sludge condition,the energy conversion rate of MEC reached119.30%,the hydrogen conversion rate and hydrogen yield of MEC increased by 1.31times,and the hydrogen production increased significantly,which increased the effect of sludge recycling.3.The chemical synthesis of struvite was the best when the reaction time was 90 min,the components(Mg²⁺,NH₄⁺and PO₄^3-)concentration were 10 mmol/L,the initial pH was 11 and n(Mg²⁺):n(PO₄^3-)=1.2:1.Phosphorus recovery in MEC sludge supernatant by ectopic struvite crystals was feasible,and the effect was the best when the initial pH was 10,the Mg²⁺dosage was 0.056 mol/L,and the NH₄⁺dosage was 0.08 mol/L.The mass of struvite crystal was up to 7.61 g/L supernatant and the top crystal purity was88.30%,77.55%of the phosphorus in the supernatant was recovered in the form of struvite.