Low-cost Rapid Start-up Method For Straw Anaerobic Digestion

Energy shortages have become a concern of the world.Biomass fuels can replace natural gas to a certain extent,and the biogas industry around the world is booming.For large scale or mega scale biogas projects,the amount of inoculum required at the start-up is huge,and it is often impossible to collect it enough at one time.There are problems of long initiation and high start-up cost,which affect the efficiency of biogas production to some extent.In order to save the start-up cost of biogas project,shorten the initiation,and also provide a theoretical basis for the popularization and using of biogas technology,This study uses rice straw and manure to mix directly activate the anaerobic digestion system without adding inoculum.And add nutrients to improve start-up speed and methane production performance,the specific results are as followed:(1)This paper mixes rice straw with cow manure or pig manure at 4 different volatile solid(VS)ratios to start up the anaerobic digestion system without inoculum.The results showed that in addition to the mixure of straw and pig manure at the VS ratio of 4:1,the other proportions mixure of rice straw and manure could be successfully started.At the same time,the lower the proportion of straw,the faster the start-up speed and the better the anaerobic digestion performance.In the case of a sufficient amount of manure,it is recommended to start the anaerobic digestion system with a mix of straw and cow manure(or pig manure)at the VS ratio of 1:2.(2)The effects of different nutrients and different additions on the start-up speed and biogas production performance of the mixure of rice straw and cow manure start anaerobic digestion system were studied.Adding 0.3 g of glucose or phosphate(in 0.8 L effective volume)is the best option to accelerate the initiation of anaerobic digestion system of rice straw and cow manure,and the time to restore biogas production is 58.62%earlier than the experimental group without added nutrients.The VS degradation rate increased by 30.30%-45.75%,and the cumulative methane production increased by 30.10%-38.46%.When the anaerobic digestion running in CSTR reactor,the methanogenic rate during the start-up process when the rice straw and cow manure were mixed at a ratio of VS 4:1 is similiar to which in the control group with the inoculum.And the methane content during the operation was higher than the control group by 10.07%-13.40%.The group of addition of glucose or phosphate compares with the group without the addition of nutrients,having higher VS degradation rate,and the time required in the start-up phase was shorter by 11.11%-22.22%.What’s more,using rice straw and cow manure mixed at the VS ratio of 4:1 to start biogas projects compared to adding inoculum can save more than 64.39%of transportation costs.(3)The microbial community structure changes during the start-up process of the anaerobic digestion system were analyzed by high-throughput sequencing.The abundance of bacterial flora and the changes in bacterial structure during the start-up process indicated that the addition of phosphate promotes the stable conversion of the flora during the initiation of the anaerobic system.The dominant strains of bacteria and archaea in each group were the same,indicating that the community structure of the anaerbic system initiated by the mixure of rice straw and cow manure was not significantly different from adding inoculum.In summary,an appropriate ratio of mixed rice straw and cow manure can be used to initiate the anaerobic digestion system without inoculum,and the addition of glucose or phosphate can speed up the start-up.This study provides a theory to support rapid start-up biogas project without inoculum.