| A large amount of kitchen wastes is generated in China every year,if these wastes are not effectively treated,it will cause environmental pollution and waste of resources.Anaerobic digestion technology can convert the organic matter in the kitchen waste into biogas for combustion and power generation,and the remaining biogas slurry and digestate can be used as organic fertilizer.Although the development of anaerobic digestion technology for kitchen waste in China has been accelerated,many problems such as poor stability and low efficiency were still exist,which directly affects economic benefits.Therefore,this paper aims at the problems of poor stability and low efficiency of kitchen waste anaerobic digestion by bioaugmentation strategies,and investigate the effect of different methanogenic culture addition dosage and frequency to improve the digestion performance and system stability;The mechanism of bioaugmentation were revealed from the aspects of microbial community succession and gene function;In addition,based on laboratory-scale experimental data,the economics of different methanogenic culture addition dosage and frequency was preliminarily analyzed.The results showed that the application of bioaugmentaion can improve the kitchen waste anaerobic digestion performance,in the term of increasing the organic loading rate?OLR?and biogas production performance.Improvement of reactors with various addition mode were different,but the digestion performance of all of them are better than that of without bioaugmentaed reactor.The system?R1?with high dosage and high frequency,i.e.,adding 0.25g VSmethanogenic cultures/L/d every 3 days had the best improvement.It has a maximum OLR of4.4g VS/L/d,with a volume biogas production and a specific biogas yield of 3.31±0.10 L/L/d and 0.75±0.02 L/g VS,respectively.High dosage and low frequency,that is,the system?R2?with methanogenic culture added 0.25 g VSmethanogenic culture/L/d every 5 days followed by the second,the maximum OLR,volume biogas production,specific biogas yield were 3.3 g VS/L/d,1.95±0.15 L/L/d and 0.59±0.05 L/g VS,respectively.The system?R3?with 0.15 g VSmethanogenic cultures/L/d every five days?low dosage and low frequency?still had a strengthening effect,and the maximum OLR,volume biogas production,and specific biogas yield were 1.5 g VS/L/d,0.86±0.08 L/L/d and 0.57±0.05 L/g VS,respectively.However,reactor without bioaugmentation could not be operated for a long–term.When the OLR was 1.0 g VS/L/d,the biogas production stopped after running to 53 d.In terms of microorganism structure,the bioaugmentation stragtegy could maintain the relative abundance of Methanosarcinales and Methanothrix,with a relative abundance of80.59%-86.29%and 80.53%-95.04%,respectively.Methanosarcinales is the only archaea that can use acetate to generate methane at the order level,and Methanothrix is an acetoclastic methanogen that can convert acetic acid to methane.The maintenance of its quantity can ensure that the acetate in the system is consumed in time,while deferring decrease of pH due to the accumulation of acetate,and created a better digestion environment for microorganisms,thereby improving the stability and performance of anaerobic digestion of kitchen waste.Bioaugmentation had little effect on the bacterial community structure.In terms of gene function,the obtained protein genes were annotated based on the KEGG database,and the differences in functional gene abundance between different samples were compared.The results showed that,in the level 3 metabolic pathway,bioaugmentation maintained a good proportion of Methane metabolism.Methane metabolism is an indispensable life activity during anaerobic digestion.Its protein gene proportion can reflect the system's methanogenic potential.When the system collapsed,the relative abundance of Methane metabolism drops dramatically,while the relative abundance of Biosynthesis of amino acids,Purine metabolism,Pyrimidine metabolism Starch and sucrose metabolism and Lysine biosynthesis at the level 3 metabolic pathway rose rapidly,which may be related to the growth of some acid–resistant bacteria.In the metabolic pathway of methanogenesis,bioaugmentation mainly enhanced and maintained the metabolic modules of from acetate to methane,from carbon dioxide to methane,from methanol to methane,from methylamine to methane,acetyl coenzyme A synthesis,coenzyme B synthesis,coenzyme M synthesis and coenzyme F420synthesis,to stable and efficient the process of methane production.Bioaugmentation did not significantly affect the level 1 and level 2 metabolic pathways of KEGG.Although bioaugmentation has shown excellent results in improving the anaerobic digestion performance of kitchen waste,it has also increased the cost of investment.To this end,the economic benefits of each methanogenic cultures addition mode in different scenarios were analyzed.The results showed that when the quantity of food waste is fixed at 21.4 tons/d,which was the daily production of Guangzhou Higher Education Mega Center,only the net income of R1 was significantly different from Rc?without adding methanogenic cultures?.The daily net income of R1 was 1766 yuan higher than Rc,while that of R2 was similar to Rc,and that of R3was lower than Rc.This indicated that the addition moded of 0.25 g VSmethanogenic culture/L/d every3 days was suitable for scenario 1.When the volume of the digester was set to 1500 m3,the economic benefit of digestion systems increased with the dosage and frequency of methanogenic culture.R1 can maximize the food waste processing capacity of the digester,so it got the maximum daily net income of 3589 yuan.However,when the volume of the digester is fixed at 1500 m3,and the quantity of food waste is not enough to be processed at the maximum OLR?Scenario 3?,the excessively high dosage of methanogenic culture will increase the economic investment of the digester.At this time,the addition dosage and frequency of methanogenic cultures should be appropriately reduced to reduce economic investment and achieve better economic benefits. |
PDF Full Text Request