Research On Chelator-assisted Electrochemical Activation Of CaO₂ To Improve Sludge Dewatering Performance

Reducing sludge water content is the most effective way to reduce sludge transportation costs and disposal difficulties.Advanced oxidation process is the key research direction in the field of sludge pre-conditioning technology before dewatering.In this project,a combined system of oxalic acid（OA）with dicarboxylic acid as chelating agent and auxiliary electrochemical（EF）activation of calcium peroxide（CaO₂）was constructed to deeply improve sludge dewatering performance.Firstly,the effects of current strength,initial p H,CaO₂and OA dose on sludge dewatering performance were investigated by designing different single-factor experiments with sludge water content（Wc）and specific resistance to filtration（SRF）as dewatering performance indicators.Then,the mechanism of the combined conditioning system to improve sludge dewatering performance was investigated in terms of the release of sludge bound water before and after conditioning,changes in surface contact angle,zeta potential,average particle size,settling performance and surface microstructure,migration of organic components in EPS and changes in sludge hydrophobicity.Finally,the mechanism of OA in the enhanced electrochemically activated CaO₂conditioning system was analyzed by monitoring the changes of Fe²⁺,total dissolved iron and H₂O₂concentrations during the reaction.The research results provide more scientific attempts and theoretical support for the combination of chelating agent and advanced oxidation technology to achieve deep dewatering of sludge,and also provide new ideas for the subsequent disposal and utilization of sludge cake.The main research results obtained in this study are as follows:（1）The EF-CaO₂conditioning system without the introduction of OA can only reduce the sludge Wc and SRF by 16.4%and 86.2%under the optimal working conditions,and the sludge at the end of the reaction is in a strongly alkaline state,which is poorly usable.After the introduction of OA,the p H rise of the reaction process was suppressed and the dewatering effect was significantly improved.The results showed that the constructed EF-CaO₂/OA combined conditioning system reduced the sludge Wc from 97.7%to 68.3%of the original sludge and SRF from 1.43×10¹³m/kg to 4.43×10¹¹m/kg under the conditions of 1A current,0.14 g/g TSS CaO₂dosing,0.18 g/g TSS OA dosing and no adjustment of the initial p H of the sludge.The sludge at the end of the reaction was still in a neutral environment,and the availability of sludge cake was obviously improved.（2）All four conditioning methods,EF,CaO₂,EF-CaO₂and EF-CaO₂/OA,could change the basic physicochemical properties of sludge,and the effects were increasing in order.After conditioning with EF-CaO₂/OA,the median particle size of sludge was reduced to 45.33μm;the zeta potential was reduced to-1.89 m V;the surface contact angle increased from 64.69°to 109.8°;the release of bound water reached the maximum;the microstructure of sludge surface changed from the dense platelet structure of the original sludge to a loose three-dimensional structure with a large number of random pores,indicating that the sludge flocs were decomposed and released bound water under the strong oxidation of the system.The surface microstructure of sludge changed from dense platelet structure to loose three-dimensional structure with a large number of random pores,indicating that the sludge floc was decomposed and released bound water under the strong oxidation of the system.The protein,polysaccharide and DNA in each EPS layer of sludge were quantified and characterized by UV spectrophotometer and 3D fluorescence spectroscopy,and it was found that the protein and polysaccharide contents of T-EPS layer of sludge conditioned by EF-CaO₂/OA decreased significantly,and the DNA content of S-EPS increased significantly,indicating that the sludge EPS and cells were damaged,which was the main mechanism for the release of bound water.By XPS,FTIR and the second-order derivative resolution enhanced curve fitting analysis of the amide I band of FTIR spectra,the protein structure of sludge conditioned by EF-CaO₂/OA was changed,and the proportion ofα-helical,β-folded and irregularly curled structures in the secondary structure was reduced,indicating that the protein hydrophobic sites were exposed,which was the most important reason for the improved hydrophobic performance of sludge.（3）It was found that the Fe²⁺and H₂O₂concentrations in the EF-CaO₂system were always at trace levels.When OA was introduced,the concentrations of Fe²⁺,H₂O₂and total dissolved iron in the EF-CaO₂/OA system increased,and the trend of change with the reaction proceeded flatly.It is proved that OA is enhancing the oxidation efficiency of the system and strengthening the sludge dewatering effect by accelerating CaO₂dissolution to improve H₂O₂yield and increasing the catalytic solubility to ensure the catalytic efficiency in two aspects.It further proves that the combination of chelating agent and advanced oxidation technology has good development potential for sludge dewatering field.