| The amount of excess sludge produced continues to increase with the continuous improvement of the degree of sewage treatment.Due to the high water content and hardly dewatering,the excess sludge in the sewage treatment plant has become a key and difficult point in the sewage treatment.In recent years,electrochemical oxidation pretreatment of excess sludge had attracted the attention due to its simple reaction conditions,easy operation,high efficiency and low cost.In this study,the treatment methods of excess sludge by electrochemical anodic oxidation and electro-Fenton oxidation technology were studied.The relevant parameters were optimized,and a better sludge cracking reduction effect was obtained.With RuO2/Ti as the anode,the optimal conditions for treating the sludge were obtained:solids content of 2.0%,current density of 40 mA/cm2,plate spacing of 2 cm,initial pH of 3.By electrolysis treatment for 40 min,the MLVSS removal rate was 15.27%,the sludge SRF reduction rate was 28.19%,and the sludge SV30min also decreased from 90.5%to 76.9%.The dewaterability and sedimentation performance were improved to a certain degree,and the degree of cracking was positively related to the improvement of sludge dewatering performance within a certain range.RuO2/Ti anode and activated carbon fiber(ACF)cathode were used to construct electro-Fenton system to pretreat the sludge.When the initial sludge solid content was 2.0-2.5%,the initial pH was 3,and the current density was 40 mA/cm2,after 40 min of electrolysis,the dewaterability of the sludge was significantly improved compared to the anodic oxidation.At this time,the MLVSS removal rate was approximately 35%,the sludge SRF reduction rate was approximately 60%,and the SV30min was approximately 55%.While the sludge dewaterability increased,the contents of soluble COD and various forms of nitrogen and phosphorus in the system increased,indicating that the electro-Fenton oxidation caused the sludge extracellular polymer and microbial cells to rupture,releasing large amounts of organic substances.With solution layer(S-EPS)and loose layer(LB-EPS)content increasing and tight layer(TB-EPS)reducing,organic matter in TB-EPS was released into S-EPS and LB-EPS by sludge cracking after anodic oxidation and electro-Fenton oxidation.The moisture bound by the EPS in the sludge was effectively released,improving the sludge dewaterability.Combined with kinetic analysis,under electro-Fenton system,not only the highest amount of EPS transferred,but also faster in rate.3D-EEM results showed that the content of humus acid-like substances in S-EPS and LB-EPS increased,and the Zeta potential of the sludge approached 0 after electro-Fenton reaction,indicating that the charged substances were condensed into polymers,which promoted the surface of the sludge with low charge,and it is conducive to sludge dewatering.The analysis of the correlation between the strength of different types of organic matter in various forms of EPS and sludge SRF showed that the intensity of humus acid-like substances and soluble microbial by-product-like substances in S-EPS showed a strong negative correlation with the sludge SRF,indicating that S-EPS was the dominant role of sludge dewatering under electro-Fenton system.Scanning electron microscopy(SEM)was used to observe the microscopic structure of the sludge.It was found that after anodic oxidation,the sludge became thinner and the structure was more compact After the electro-Fenton action,the sludge was broken into fine pieces of flake,no complete structure and pores were formed,and the combined water transformed into free water,which reduced the water holding capacity of the sludge and realized the separation of sludge and water.The results showed that the electro-Fenton oxidation technology improved the sludge dewaterability to a certain extent compared to the anodic oxidation,the SRF reduction rate increased by about 30%,and the MLVSS removal rate increased by about 20%.The degree of sludge reduction was significant. |
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