Basic Application Research Of Anaerobic Co-Digestion Of CaO₂ Pretreated Sludge And Municipal Organic Waste

With the accelerated urbanization in China,the sludge production in municipal wastewater treatment plants is increasing rapidly,and more attention has been paid to effectively realize the "reduction,stabilization and resourceization" of sludge.Anaerobic digestion of sludge treatment can obtain both environmental and economic benefits.However,the anaerobic digestion of single sludge has some problems such as difficult hydrolysis,poor system stability,and poor gas production,so most previous studies have attempted to pretreat it or co-digest it anaerobically with other suitable organic matter.CaO2 as an oxidant can significantly promote sludge hydrolysis,but increase the pH of sludge significantly,thus affecting subsequent anaerobic digestion probably.In view of this,in this study,the pretreated sludge was co-digested with acidic food waste and fecal sludge,from municipal organic waste.This study is expected to provide the technical support for incremental methane production in anaerobic digestion of sludge pretreated by CaO2.The main results and conclusions obtained in the experiment are as follows:(1)When anaerobic co-digestion of CaO2 pretreatment sludge with food waste,the system gas production is significantly improved when the ratio of kitchen waste to CaO2 pre-treated sludge is less than 7:3 and 9:1(based on volume).Among them,the treatment group with the sludge to food waste volume mixing ratio of 9:1(V-9:1)had the highest cumulative methane production of 348.4 mL/g VS,which was 206.15%higher than that of the control group(CK);and the average methane content reached 64.26%,which was 2.28%higher than that of the CK.Meanwhile,the fit results of the modified Gompertz model showed that the maximum methane production potential(P0)and maximum methane production rate(Rmax)of the V-9:1 group were increased by 245.19%and 61.48%,respectively.(2)When CaO2 pretreated sludge was anaerobically co-digested with fecal sludge,the gas production effect of the system gradually increased with the increase of the fecal sludge ratio.Among them,the best gas production was achieved in the treatment group with the sludge to fecal sludge volume mixing ratio of 5:5(V-5:5),the cumulative methane production was 370.4 mL/g VS,which was 157.94%higher than that of the control group(CKss);and the average methane content was 70.14%,which was 5.59%higher than that of the CKss.The fit results of the modified Gompertz model showed that the P0 and Rmax of the V-5:5 group were increased by 205.44%and 47.51%,respectively,compared to the CKss group.(3)Methane production was enhanced in anaerobic co-digestion of CaO2 pretreatment sludge with food waste and fecal sludge,respectively,mainly due to the significant increase in total volatile fatty acids(TVFAs)and dissolved chemical oxygen demand(SCOD).Compared to fecal sludge,the hydrolysis of kitchen waste increased the SCOD and TVFAs concentrations more significantly,with the SCOD and TVFAs concentrations increasing by 127.87%to 567.21%and 104.96%to 635.30%,respectively,with acetic acid and butyric acid as the main acid-producing types.However,significant increases in the concentration of TVFAs can also prolong the systemic lag period(λ)and even risk acid inhibition.(4)The addition of suitable proportion of food waste and fecal sludge can return the system pH to the suitable methanogenic range(6.8～7.2)in the early stage of anaerobic digestion.Moreover,the introduction of food waste and fecal sludge can significantly increase the TAN concentration in the system.Meanwhile,the FAN concentration increased significantly in the late stage of anaerobic digestion,but it did not exceed the threshold value of gas production inhibition(≤600 mg/L),so there was no risk of gas production inhibition.(5)The test results of anaerobic co-digestion of CaO2 pretreated sludge with food waste and fecal sludge showed that the combination of CaO2 pretreated sludge with fecal sludge and food waste in the ratio of 4:2:1(based on solids content)was the optional condition.Under this condition,the cumulative methane production reached 354.4 mL/g VS,an increase of 186.04%compared with the CKss.Meanwhile,the average methane content in the biogas reached 70.59%,a further increase of 8.14%compared with the CKss.