| With the increasing production of organic waste(such as sluge and food waste)in China,treating organic waste economically and scientifically becomes an urgent problem.Anaerobic digestion can not only realize organic waste reduction and harmlessness,but also produce biogas to realize resource utilization,which has a broad application prospect.However,the efficiency of organic waste anaerobic digestion is often low,which is often limited by the hydrolysis stage,the influence of high salt / oil content and the property of single material.Therefore,in order to improve the efficiency of anaerobic digestion gas production,this paper optimizes the anaerobic digestion of sludge through pretreatment,studies the influence of salt and oil on the anaerobic digestion of food waste with the optimization methods,and studies the anaerobic co-digestion of sludge and food waste.Finally,dynamic analysis and modeling are carried out to provide theoretical and technical reference for the optimization of organic waste anaerobic digestion.In this paper,first of all,in view of the speed limit of the hydrolysis stage in the process of anaerobic digestion of sludge,pretreatment is carried out to improve the hydrolysis rate,promoting the process of anaerobic digestion of sludge,and improving the gas production of anaerobic digestion.The advanced sulfate radical oxidation was researched,and the results showed that the effect of iron foil was better than iron powder in the zero valent iron-persulfate oxidation pretreatment,the cumulative methane production of optimum dosage was 53.6% higher than that of the blank group,and the dewaterablity of sludge was also improved.In the ultrasonic pretreatment,the lower the ultrasonic frequency was,the better the disintegration effect was,and under the same energy consumption,the pretreatment effect of low power with long time was better than that of high power with short time,under the optimum pretreatment conditions(20 kHz,325 w,10 min),the cumulative methane production was 78.3% higher than that of the blank group.In the alkaline pretreatment,it was found that when the NaOH addition was more than 5 g/L,the disintegration effect was not significantly improved,and when the NaOH addition was too large,the anaerobic digestion was inhibited.The gas production increased the most with the addition of 10 g/L NaOH,and the cumulative methane production increased by 31.6% compared with the blank group.Based on the study of the influence of salt on the anaerobic digestion of food waste,three methods of acclimation,osmoprotectant and water washing desalination were put forward for optimization.The experimental results showed that the biogas production can be slightly increased by the appropriate concentration of sodium,but the excessive concentration of sodium ion can significantly inhibit the effect of anaerobic digestion.In the process of acclimation,the relative abundances of kosmtoga belonging to Thermoogae with Lyelina and Longilinea belonging to Chloroflexi increased gradually;the relative abundances of Methanobcterium and Methanocorpusculum,belonging to hydrogen nutrition type methanogens,increased gradually.In the process of acclimation,the microbial community increased the proportion of bacteria for hydrolysis and nutrition provision,and obtained small molecular organics by hydrolyzing large molecular organics,and provided bacteria for nutrition provision to adapt to the high sodium environment.After acclimation,the methane production increased by 63.6%.Among the three osmoprotectants(betaine,polyethylene glycol and salicylic acid),betaine had the best effect.At the concentration of 5 g/L and 8 g/L sodium,betaine can increase the cumulative methane production by 36.4% and 45.8%.Water washing is an effective desalination method.Through the experimental study,the best technological condition of water washing was m(water)/ m(food waste)= 2,10 minutes stirring and shaking,and centrifuging at 4000 rpm for 10 minutes.The sodium content of food waste after water washing desalination was reduced from 8 g/L to 2.02 g/L.Through the study of the effect of oil on the anaerobic digestion of food waste,it is found that high oil content has certain inhibition on the anaerobic digestion of food waste.Therefore,the methods of acclimation and calcium chloride additon were proposed for the anaerobic digestion of high oil content food waste.The experimental results showed that the increase of oil content was beneficial to the increase of methane production,but the increase of oil content also inhibited the anaerobic digestion,and the oil utilization rate reached the highest at 5% oil content.In the process of acclimation,the relative abundances of Anaerolinea,Longilinea and Clostridium,which belong to Chloroflexi,increased gradually;the relative abundances of Methanobacterium,which belong to hydrogen nutrition type methanogens,increased gradually.The proportion of bacteria that decompose LCFA and provide nutrition is increased,which makes the bacteria adapt to the environment with high oil content.After domestication,the methane production is increased by 24.9%.The addition of appropriate amount of calcium chloride was beneficial to the anaerobic digestion biogas production of high oil food waste.4 g/L of calcium chloride was the optimum dosage,which can increase the anaerobic digestion methane production by 23.9% compared with the blank group.Based on the investigation of the optimal C/N of the anaerobic co-digestion,the gas production was optimized by the two methods of the thermophilic-mesophilic anaerobic codigestion and the addition of bentonite.The experimental results showed that when the solid content ratio of food waste and sludge was 60:40(C/N was 15.5),the anaerobic co-digestion had the best gas production effect,compared with single sludge or food waste anaerobic digestion,the cumulative gas production of co-digestion increased by 45.2% and 20.9% respectively.The thermophilic-mesophilic two-phase anaerobic co-digestion combined with high hydrolysis acidification rate in the early stage of thermophilic anaerobic digestion and stable VFA content in the middle and late stage of mesophilic anaerobic digestion increased gas production by 50.3% compared with that of mesophilic anaerobic digestion.A proper amount of bentonite can prevent the substrate from expanding by forming flocs,alleviate the pH fluctuation,absorb sodium ions and release calcium ions,so as to improve the gas production efficiency.When the amount of bentonite is 10 g /L,the gas production efficiency is the highest,which is 47.7% higher than the blank group.According to the fitting results,we found that Gompertz equation had some advantages in fitting accuracy and dynamic significance.The maximum methane production rate and lag time in Gompertz equation were used to evaluate the kinetics of various anaerobic digestion gas production optimization technologies.The results showed that the optimized experimental group increased the maximum methane production rate and reduced the lag time.The kinetic parameters provide a reference for the establishment of anaerobic digestion model.Finally,based on ADM1(anaerobic digestion No.1 model),the model was built on Aspen Plus software,and CSTR module was used to simulate the anaerobic digestion reactor,in which all the reactions are added.In addition,calculation blocks wrote the calculation methods of reaction rate in FORTRAN language,and associated them to each reaction equations.Combined with the kinetic parameters and the reaction rate correction calculation module,the simulation accuracy is high.Use this model to optimize the composition of feed,the results showed that the optimal ratio is protein: carbohydrate: fat = 2:7:1.Through the optimization of anaerobic digestion of organic waste,better methane production effect can be obtained,which has a broad application prospect. |
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