Anaerobic Co-digestion Of Sludge And Food Waste And Improved Dewaterability Of Anaerobic Digestate As Well As Phosphorus Resource Recovery

By December,2020,production of 80%moisture content sewage sludge has exceeded6.00×10⁷ tons in China.Anaerobic digestion is an effective way for sludge stabilization and resource utilization.However,due to the low content of organic matter（generally 40%～60%）of sludge in China,anaerobic digestion of sludge often faces the dilemma of low biogas yield in engineering application,which largely limits the implementation of this technology.In addition,the increased alkalinity,smaller particle size and more difficult solid-liquid separation（dewatering）of the products after anaerobic digestion bring great challenges to the subsequent transportation,composting and incineration.Therefore,how to improve the efficiency of anaerobic digestion of sludge and improve the dewaterability of digestion products is an urgent technical problem.In this paper,sludge and food waste were mixed for anaerobic digestion.Effect of material mixing ratio on gas production characteristics of anaerobic digestion,mechanism of thermally activated persulfate to improve the dewaterability of anaerobic digestate and effect of modified biochar on adsorption and removal of phosphorus from filtrate of anaerobic digestate were investigated in this study.The purpose of this study is to provide a technical reference for the collaborative and efficient anaerobic treatment of sludge and food waste.The main results are as follows:（1）Anaerobic digestion of sludge and food waste can significantly improve biogas production and methane production.Under the optimal mixing ratio of sludge and food waste of 1:1（VS）,the cumulative biogas production and methane production were 430.1 m L/g VS and 218.1 m L/g VS,which were 94.9%and 77.5%higher than that of anaerobic digestion of sludge alone.The addition of food waste accelerated the hydrolysis of materials and improved the conversion efficiency of organic matter,and the concentration of SCOD in fermentation broth was significantly increased,The removal rate of VS increased from 30.3%to 52.7%.However,when the proportion of food waste in the system is relatively high,it is easy to cause the accumulation of VFAs,thus reducing the p H of the system and affecting the whole methanogenic process.（2）Thermally activated PDS oxidation significantly improved the dewaterability of the sludge-food waste anaerobic digestate,and that the extent of the improvement in the dewaterability increased with the increase in temperature.The optimal conditions for thermally activated PDS treatment were as follows:temperature of 70℃,the reaction time of 240 min,and sodium persulfate dosage of 4 mmol/g DS.After the PDS treatment,the CST of the anaerobic digestate decreased from 1064.9 s to 39.4 s.The moisture content of sludge cake after air compressor pressure filtration decreased from 82.4%to 60.1%,and the supernatant is clear.The heavy metal concentration in the filtrate was all within the emission standard range,but the phosphorus concentration in the filtrate increased from 4.7 mg/L to258.7 mg/L.Cl^-had little effect on CST of thermally activated PDS,but CO₃^2-and HCO₃^-had different degrees of inhibition on CST of thermally activated PDS.These results suggest that during thermally activated PDS treatment,the production of SO₄^?-and?OH resulted in the destruction of the floc structure of anaerobic digestate and protein degradation in TB-EPS,which may be responsible for the improvement in the dewaterability of the sludge-food waste anaerobic digestate.（3）The modification method of biochar has great influence on the effect of phosphorus removal by adsorption.The Mg modified biochar can effectively adsorb phosphorus in the filtrate,and reach the adsorption equilibrium in about 8 h.The adsorption capacity at equilibrium is 28.4 mg/g.the adsorption kinetic process conforms to the pseudo second order kinetic equation.The phosphorus adsorption is mainly chemical adsorption,and the isothermal adsorption process conforms to the Langmuir isothermal adsorption equation,which is monolayer adsorption.The combination of phosphorus with biochar through electrostatic attraction and precipitation may be responsible for the removal of phosphorus in the filtrate.