Study On Pretreatment Of Sludge By Potassium Ferrate Combined With DBD Plasma

A large amount of excess sludge is produced in the daily operation of sewage treatment plant.The effective disposal of excess sludge is particularly important for environmental protection.How to efficiently break the sludge and release the organic matter in the sludge for subsequent treatment and disposal is the main research direction of many researchers.Based on the combination of advanced oxidation method and chemical pretreatment method,this study focused on the factors influencing the cracking effect of sludge pretreatment and the mechanism around the efficiency of excess sludge cracking and anaerobic fermentation.Potassium ferrate is widely used as a strong oxidant,which has the characteristics of strong oxidation ability,non-toxic by-products,decolorization and deodorization.Dielectric barrier discharge(DBD)plasma treatment is a kind of advanced oxidation method widely used in sewage and sludge treatment experiments,which has the characteristics of green environmental protection,fast onset,rich active substances and so on.Considering that the activation factors such as UV light,· oh and ozone can not be fully used in the discharge reactor,and some studies have shown that microwave,ozone,alkali and other active substances can promote the activation of potassium ferrate.Therefore,in this paper,DBD plasma and potassium ferrate are combined to form a coupling system to explore the effect of the coupling system for sludge pretreatment.It provides a reference for the follow-up treatment of domestic sludge.The main research results are as follows:(1)Under the condition of discharge voltage of 11 k V and frequency of 12 k Hz,after pretreatment with DBD plasma for 30 min,the release of SCOD reached the maximum of 865.4mg/L,and the protein concentration,polysaccharide concentration and DNA content of sludge supernatant were increased to 215.21mg/L,99.59mg/L and 533.29μg/L,respectively.Meanwhile,the sludge dewatering performance was greatly improved,and the CST value decreased from 132.6s to 30.5s.(2)The experimental data showed that only potassium ferrate could effectively destroy sludge flocs and release organic matter.When potassium ferrate dosage was1000mg/L,the peak value of SCOD and protein in sludge supernatant reached1010.96mg/L and 230.02mg/L respectively.When potassium ferrate dosage was800 mg /L,the peak values of polysaccharide and DNA in sludge supernatant were156.69mg/L and 1000.46μg/L respectively.The peak value of VFAs was 367.14mg/L at the dosage of 600mg/L,which may be due to the decrease of VFAs content due to the reaction between VFAs and excessive potassium ferrate in liquid phase.(3)Design expert was used to analyze the correlation of the influencing factors of the pretreatment experiment.Under the optimal conditions of coupling treatment,the peak values of SCOD,protein,polysaccharide and DNA in the sludge supernatant increased by 65.38%,26.35%,17.21% and 30.52% respectively compared with potassium ferrate pretreatment alone.According to the RSM optimization experiment,there is a significant interaction between the discharge voltage,frequency and potassium ferrate dosage.According to the experimental results,the model was established to predict the optimal parameters of the combined system under the experimental conditions: potassium ferrate dosage 714.63mg/L,potassium ferrate reaction time 37 min,discharge frequency 11.61 k Hz,discharge voltage 10.63 k V,discharge time 17.18 min.According to the predicted conditions,the difference between the measured results and the predicted values is less than 5%.(4)Anaerobic fermentation experiments were carried out on sludge pretreated by different methods.The results showed that the gas production of untreated sludge was58.5m L in 30 days of anaerobic digestion.The peak gas production of sludge pretreated by DBD,potassium ferrate and combined pretreatment reached 271.5m L,219.8m L and389.2m L respectively,which was 4.6,3.7 and 6.6 times of the original sludge.