Renovated Sludge Pretreatment Technology Based On The Fenton-like Processing Methed With Fe³⁺

As a by-product of sewage treatment,sludge has the characteristics of high yield,high pollution and high water content.Therefore,pretreatment of sludge to improve sludge dewatering,sedimentation and cracking performance so that sludge subsequent treatment is the primary task of sludge treatment.Fenton process is widely used in sludge pretreatment process,but there are some problem in Fenton process,such as low utilization of Fe2+and low pH value.In order to solve the problem of traditional Fenton process,concentrated sludge is used as research object,forming a Fenton-like sludge pretreatment technology by modifying the Fenton catalyst.Screening different metal catalysts,and investigating the effects of Fenton-like dosage,reaction time,stirring speed,dosing order and mode on sludge pretreatment,determine the optimal reaction conditions for Fenton-like sludge pretreatment.Preliminary study on the mechanism of Fenton-like sludge pretreatment technology,according to cracking rule of EPS,sludge particle characteristics and the change of sludge water form.The main results are as follows:(1)Composition of seven Fenton-like reagents,H2O2 for oxidant and Fe2+?Fe3+?Cu2+?Fe?eu2+Fe2+?Fe2+Fe3+?Mn2+for catalyst.The improvement of sludge dewatering performance(such as the water content of sludge and mud cake,SRF and CST),settlement performance for example,SV and SVI),and the cracking performance(for instance,the sludge concentration,SCOD and EPS)were studied.The results showed that the optimum metal catalyst was Fe3+,the water content of the sludge and mud cake,as well as the CST tend to decrease by 97.94%,77.87%,and 17 s,whereas the parameters of SV and SVI tend to be reduced to 29%and 49.15 mL/g,the removal efficiency of MLSS and MLVSS has been made a lot more reduced to as much as to 41.35%and 40.91%,accordingly and respectively.On the other hand,the high concentrations of SCOD as well as the proteins and polysaccharides of EPS in the sludge prove to be supernatant during the Fe2+Fenton-like process.All in all,the Fe3+Fenton-like process has obvious improvement effect on sludge dewatering,settlement and cracking performance.(2)The single factor experiment of sludge pretreatment effect showed that the optimal reaction conditions of Fe3+ Fenton-like reaction were as follows:the optimum dosage of H2O2 was 90 mmol/L,the molar ratio of H2O2/Fe3+was 3:1,the reaction time was 60 min,the stirring speed was 40 r/min,the Fe3+was added first,and then the reagent was added twice.Under this condition,MLSS was 4.63g/L,CST was only 12.9s and SCOD was 302.76mg/L.(3)Based on Box-Behnken central composite design principle,response surface methodology was used to design three-factor and three-level tests with Fenton-like agent dosage,reaction time and stirring speed as influencing factors and CST as response value.The significance order of the three influencing factors of Fe3-Felton-like reaction is the reaction time>H2O2/F3+molar ratio>stirring speed,the interaction between H2O2/Fe3+ molar ratio and stirring speed was the most significant.The optimal reaction conditions of Fe3+ Fenton-like sludge pretreatment technology were:H2O2/Fe3+ molar ratio 2.7:1,reaction time 63min and stirring speed 40r/min.Under these conditions,CST was only 12.78s.The relative error between the test results and the predicted results is 2.8%,indicating that the model can more realistically reflect the impact of various factors on CST.(4)The mechanism of Fe3+ Fenton-like sludge pretreatment technology Was studied by EPS,particle size distribution and the change of water form.The results showed that after Fe3+Fenton-like pretreatment,the concentration of polysaccharides and proteins in S-EPS and LB-EPS increased,the concentration of polysaccharides and proteins in TB-EPS decreased,and a large number of TB-EPS transformed into LB-EPS and S-EPS.The median particle size,average surface area particle size and average volume particle size of sludge decreased,while the specific surface area increased,and the bound water content in sludge decreased.According to the above results,it can be considered that the mechanism of Fe3+rFenton-like is that Fe3+catalyzes the production of a large amount of·OH by H2O2,the sludge cells are oxidized and cracked,a large amount of EPS is released,and the combined water in the sludge cells and EPS is converted into free water and released.The structure of sludge floes is destroyed,and the large particles become small particles,the uniformity of sludge particles is improved,which is conducive to sludge collision and flocculation.In summary,Fe3+Fenton-like sludge pretreatment technology can effectively improve the dewatering,settlement and cracking performance of sludge.