Effects Of Temperature And Organic Loading Rate On Co-digestion Of Food Waste And Waste Activated Sludge

In China,increasing rates of food waste(FW)and waste activated sludge(WAS)production have exceeded 10% in recent years,due to industrial development and urbanization.Among them,FW is labile and readily biodegradable organic waste which is difficult to be collected,transported and treated.WAS is the byproduct of waste water treatment process,it contains a lot of pathogens,heavy metals and other toxic compounds.Anaerobic digestion(AD)is more sustainable and is an efficient way to realize harmlessness,reduction and resource utilization.Compared with mono-digestion,co-digestion of FW and WAS has been demonstrated to be more efficient and stable because of the dilution of toxic compounds,the improvement in nutrient balance and the synergistic effect of the microorganisms.Temperature is a crucial factor to affect the AD process,therefore,the effects of temperature on co-digestion of FW and WAS was conducted by batch tests in order to know to kinetics of AD process involving hydrolysis,acidogenesis,acetogenesis and methanogenesis.The kinetic parameters were obtained by simulation using Gompertz equation.Results showed that high temperature significantly accelerated the hydrolysis rate,but the higher hydrolysis rate also resulted in the more severe accumulation of VFAs.The methane yield of mesophilic and thermophilic co-digestion was 296 and 546 mlCH4/gTS,respectively.Both of them were higher than the theoretical value,indicating co-digestion was more efficient than mono-digestion.In order to the effects of temperature and OLR on the stability and efficiency of co-digestion of FW and WAS,the long-term experiment was conducted in continuous stirred tank reactor(CSTR).The OLR was increased from 2.69 to 15.93 gVS/L/d by shortening HRT from 30 d to 5d.The results showed that with OLR increasing,the methane yield increased first and then decreased.The me thane yield of thermophilic system was obviously higher than mesophilic system,and the maximum methane yield were 407.92 mL/gVS and 357.86 mL/gVS,respectively.VFAs accumulation occurred under both mesophilic and thermophilic condition with OLR increasing,and butyrate was the main component of accumulated VFAs.After the OLR increased to 15.93 gVS/L/d,thermophilic system was still robust,while mesophilic system has been failure accompanied by the sharp decrease of pH.The results of specific methanogenic activity(SMA)experiments at different stages showed that acetate could be converted to methane rapidly under both thermophilic and mesophilic conditions,but the SMA of butyrate and propionate was significantly lower than acetate.The low conversion rate from butyrate to methane should be the main reason for the accumulation of butyrate at high OLR.Finally,the energy consumption analysis indicated that the energy consumption turned to production when the OLR was higher than 5.05 gVS/L/d.The net energy production of thermophilic system was significantly higher than of mesophilic system under high O LR,indicating thermophilic system has the advantages of high methane production and stability.Therefore,thermophilic co-digestion of FW and WAS greater prospects.