Study On Enhanced Residual Sludge Dewatering Technology Based On Pre-oxidation Conditioning

The rapid urbanisation of China in recent years has led to a dramatic increase in domestic wastewater,and the treatment of wastewater inevitably generates a large amount of sludge,and an integral part of the subsequent treatment and disposal of sludge is sludge dewatering.In general,the residual sludge from wastewater treatment plants is characterised by high hydrophilicity,high organic matter content,fine particles and high bound water content,and the polymer wrapped around the surface of the sludge particles forms a barrier separating the free water from the bound water,which affects the release of bound water,thus resulting in poor sludge dewatering.Therefore,how to improve sludge dewatering has become a popular topic in the field of sludge disposal.In this thesis,a new sludge conditioning agent and its mechanism of action are investigated to improve the dewatering properties of sludge.In this study,strong oxidants potassium permanganate（KMn O₄）and Na Cl O were used in combination with acid conditioning treatment and Fe Cl₃,respectively,to improve sludge dewatering and to investigate its dewatering mechanism,with the main research content as follows.（1）The effects of sludge p H adjustment and the addition of KMn O₄ on the oxidation of sludge extracellular polymer（EPS）were investigated and the combined use of p H and KMn O₄ to condition sludge to improve its dewatering properties was investigated.It was shown that p H/KMn O₄ oxidation of sludge changed the distribution of proteins and polysaccharides in EPS and that the combined conditioning was effective in improving the dewatering performance of the sludge.The protein content of soluble EPS（S-EPS）increased and the protein content of loosely bound EPS（LB-EPS）and compact EPS（TB-EPS）decreased as the p H of the sludge was reduced and KMn O₄at 0-25 mg/g TS was added.The experimental data showed that at p H 3.0 and KMn O₄addition of 25 mg/g TS,the sludge specific resistance decreased from 12.94 x 10 ¹²m/kg to 9 x 10 ¹¹ m/kg and the capillary water absorption time（CST）decreased from167.3 s to 30.1 s.The water distribution of the sludge was significantly changed by low magnetic field NMR.The overall shift to the right with time indicates a reduction in bound water in the sludge.After acidification and oxidation of the sludge,the C-OH and C-O peaks in the S-EPS are enhanced,the zeta potential of the sludge is less negative,the bound water content is reduced and the dewatering of the sludge is significantly improved.Finally,the correlation data for each indicator was obtained by analysis.（2）The principle of improving sludge dewatering by adding different combinations of agent conditioning was investigated with the oxidant coupling potential Na Cl O-Fe Cl₃.The dewatering effect of the sludge was improved by pre-oxidising the sludge EPS with Na Cl O and destroying the proteins and other substances in the EPS,followed by the addition of Fe Cl₃ to reduce the sludge Zeta potential.The highest dewatering efficiency was achieved when Fe Cl₃ was added at 100mg/g TS,and the specific resistance of the sludge decreased from 1.86×10 ¹⁰ m/kg to 3.24×10 ⁸ m/kg in the original sludge;the absolute value of the Zeta potential also increased,and the CST decreased from 125.3 s to 35.3 s in the original sludge.The protein and polysaccharides in the S-EPS layer gradually increased after the oxidative coupling potential adjustment of the sludge,with the LB-EPS layer showing the most significant decrease in protein and polysaccharides,and the TB-EPS layer also showing a decrease in protein and polysaccharides.In order to understand,more intuitively,the changes inside the sludge cells,firstly,the degree of cell lysis using DNA characterisation,and it was found that potentially coupled cell lysis using Fe Cl₃ after first oxidation was effective;finally,cell lysis was observed using cell visualisation depth,and it was found that at the Na Cl O dosing level of 50mg/g TS and Fe Cl₃ dosing level of 100 mg/g TS,the This result reflects that the oxidative coupling potential has a significant role in the improvement of sludge dewatering performance in the NaClO-FeCl₃ system.