Optimization Of Methane Fermentation Parameters And Microbial Community In Ethanol-Methane Coupling Fermentation Process From Food Waste

The disposal of large quantities of food waste has caused significant environmental pollution and financial cost globally.Compared with conventional disposal methods(including landfill,incineration,and composting),fermentation and anaerobic digestion is a promising technology for food waste management.In china,approximately 6.0*107 tons of food waste are generated per annum.Ethanol fermentation from food waste is a plausible alternative for management and disposal of this waste.However,the major challenge of ethanol fermentation from food waste was the dispose of huge amounts of wastewater,which has special characteristics of saline and oil contents.The discharge of ethanol wastewater(stillage)without appropriate treatment would cause serious pollution of water resources and soil.Wastewater treatment or dewatering of large amounts of liquid waste is costly and requires a high-capacity treatment facility or energy-intensive processing.With the above background,integrated system optimization study was planned to evaluate potential of bioethanol and biomethane production,through ethanol-methane coupling fermentation system.Furthermore,study of the relationship between process performance and dynamics of microbial communities could maintain stability and sustainability of this system.Ethanol obtained from food waste is 49.5 g/L for 9.6 g VSin and pH 5.4,and methane yield of stillage is 569 mL/g VS.The methane potential production was simulated by modified Gompertz model.Rmax indicated the maximal methane production rate from stillage was(51.45 mL/g VS/d),and the rate constant k in the first order kinetic model,which indicated the biodegradability efficiency of stillage contents was high(0.189/d),suggesting rapid degradation of organic contents and elevated methane yield.Further,volatile fatty acids(VFAs)concentrations had no inhibition effect because of the stable pH values ranging from 7.0 to 8.02,in favor of methane production.Ammonium-nitrogen concentration showed remarkable inhibition for methane production in the coupling system after 20 days of progress with concentration of more than 2000 mg/L.Magnesium hydroxide(Mg(OH):)succeeded for ammonium ions removal from anaerobic digestion system by three different methods,with removal rate of more than 80%and the corresponding methane yield had increased 2-fond.Biochemical methane potential tests(BMP)were conducted to be perceived that pH and temperature play an important role governing methane production from ethanol wastewater.The highest yield was 164 ml/gVS,obtained at temperature 550C and pH 7.The microbial communities in ethanol-methane coupling fermentation reactor showed that Clostridia(hydrogen producer)was the dominant species throughout the whole process at genus and phyla level.In addition,the high abundance of archaea methanogens species(aceticlastic methanogens)with more than 92%can contribute to the utilizing both acetate and hydrogen to produce methane.Moreover,lactic acid bacteria species(Lactococcus)was dominate in ethanol reactor(35%),suggesting the efficient conversion of food waste to lactic acid,which could continue its conversion to ethanol.Interestingly,high amount of ammonia,salts,and VFAs(including high acetate)could promote SAO pathway in coupling fermentation system.Results for ethanol fermentation using recycled water indicated that fermentation time was reduced by 50%using both electrodialysis effluent and microbial fuel cell effluent recycling.Among the different recycled water,electrodialysis effluent recycling in ethanol fermentation motivated yeast growth;yielding highest ethanol of about 47 g/L.The pH changes in the fermentation systems during 60h using the different recycled waters were found within the optimal range of ethanol fermentation(pH 4.0-5.0).Moreover,the highest content of acids found in the fermentation systems were 15 g/L and 1 g/L lactic and formic acid respectively,less than inhibition values reported.There was no significant inhibition on ethanol fermentation system due to VFAs presence.This study will aid the development of an integrated treatment plant for food waste and biofuel production.Finally,LCA was performed to assess the environmental impact of ethanol-methane coupling fermentation system.The characterization permits seeing the percentage contribution of each process to the total environmental impact of a given system.Acidification represents the highest impact category(71%)in the ethanol fermentation stage(S1).Global warming potential accounts the highest contribution impact category(72%)in the methane fermentation stage.The outcomes depicted that ethanol-methane coupling fermentation from FW has high emissions towards GWP and AP.At comparative basis,methane stage has higher GWP and AP emissions than ethanol stage.While,ethanol has more POCP emissions than methane.