Pretreatment Of Municipal Sludge By Ti/PbO 2 Anodization And Its Combined Method

As an inevitable byproduct of sewage treatment,municipal sludge often possesses the undesirable properties such as high moisture content,dehydration difficulty,large output,high processing costs.Then the high content of microbial pathogens easily contaminated food chain,and the perishable stink could pollute the environment.The treatment and disposal of municipal sludge has been regarded as the key difficulty in sewage disposal.Therefore it is urgent to explore efficient methods for realizing deep dehydration of municipal sludge and reducing the harm to environment.Up to now,several strategies have been developed for sludge treatment such as physical method,chemical method,biological method and combined method.However,these methods often possess some disadvantages including high energy consumption,secondary pollution or poor stability.In recent years,electrochemical oxidation technology has been regarded as a promising strategy in the field of sludge pretreatment due to its high efficiency,low energy consumption,mild reaction condition and simple operation.In this work,benefited from the excellent conductivity,robust chemical stability and high oxygen evolution potential,the Ti/PbO₂ was choosed as the electrode for the pretreatment of municipal sludge and the electrooxidation property of the Ti/PbO₂ on sludge pretreatment were investigated.The degree of sludge dewaterability was quantified by the capillary suction time（CST）and the moisture content of filter cake.And the effects of the operating parameters on sludge pretreatment performance were investigated including electrolytic voltage,electrode gap,electrolyte species,and the dosage of electrolyte respectively.The sludge oxidation mechanism was discussed by measuring the concentration of protein and polysaccharide in the supernatant of sludge and the surface images obtained by atomic force microscope（AFM）.The results showed that the optimal parameters were 20 V of voltage,2 cm of electrode distance,0.6 g NaCl and 20 min of electrolysis time.Under these optimal parameters,the CST of sludge has decreased significantly by 90 ± 3%,the moisture content of filter cake has been decreased to 49 ± 3%,the dewaterability of the municipal sludge shows effectively improved.Subsequently,the combined method of Ti/PbO₂ and H₂O₂（Ti/PbO₂-H₂O₂）was applied to pretreat the municipal sludge.The individual effect of four process parameters,i.e.dosage of hydrogen peroxide,electrolysis voltage,dosage of sodium chloride and stirring speed on capillary suction time（CST）and water content of sludge were investigated.The morphology of sludge was observed by scanning electron microscopy（SEM）.The results revealed that the CST value of sludge decreased the most significantly by 90% and the moisture content of sludge cake was below 40% as well as settling velocity was below 30% under the optimal operation conditions（1 mL H₂O₂,20 V voltage,0.6 g NaCl,mixing at 100 r/min）.The change of concentration of protein and polysaccharide as well as the SEM images of sludge showed that extracellular polymeric substances（EPS）and microbial cell of sludge was deformed and the dewaterability of sludge was improved due to the release of the cell interstitial water from sludge.In addition,the pretreatment of municipal sludge by Ti/PbO₂-O3 electrooxidation were investigated by choosing capillary suction time（CST）,moisture content of filter cake and settling velocity as a metric of the sludge dewaterability under the optimization of ozone flow,electrolysis voltage and dosage of NaCl.Meanwhile,the mechanism of sludge dewaterability was discussed according to the change of concentration of protein and polysaccharide as well as the microscopic image of sludge floc structure.The results indicated that the sludge dewaterability can be efficiently improved with CST value（10 ± 2 s）,moisture content of filter cake（35 ± 2%）and settling velocity（below 30%）under the optimal reaction conditions,i.e.ozone of 100 mL/min,voltage of 20 V,0.6 g Na Cl and electrolysis time of 20 min respectively.