Biogas Production And Microbial Community In Solid-state Anaerobic Digestion Of Swine Manure

As an agricultural country,the rapid development of intensive and large-scale aquaculture.about 3.49 billion tons of animal manure and 992 million tons of straw waste being generated annually in China.Unreasonable treatment and disposal have caused serious environmental pollution.Animal manure and straw are the better biomass resources which contain a great deal of organic matter.Anaerobic digestion?AD?is an effective method which achieves resource utilization of agricultural waste and relieves the pressure of environmental pollution simultaneously in a number of processing technologies.Solid-state AD?SS-AD?has the lower energy consumption,higher organic loading rate and biogas production than liquid AD?L-AD?,therefore it is widely used in the treatment of agricultural waste.This paper carry out the SS-AD experience of different treatments which sole-swine manure,mixture of swine manure and straw,layered seeding with the mixture.Study the effect of different treatments on fermentation performance.Meanwhile,reveal the community structure and variety of microbial by the Miseq high-throughput sequencing,and clarify the relationship with biogas production.In addition,three kinetic models which included first-order kinetics,modified Gompertz and Cone models are chosen to fit the methane production.The main results are as follows:?1?Layered seeding can shortening the start-up time,increase the biogas production.The time that CH₄ content and specific methane yield?SMY?of layered seeding reach the maximum earlier than the sole,and the cumulative SMY which 89.0%higher than the sole?111.90 mL/g VS?is 211.48 mL/g VS.Because of the acidification,the SMY of the mixture is always lower,and the CH₄ content which increase slowly is not reach 50%until on the 70th.?2?Layered seeding can improve the process of hydrolysis,acidogenic and methanogensis,relieve the acid inhibition,and increase the stabilization of fermentation system.The soluble chemistry oxygen demand?SCOD?of the layered seeding,the mixture and the sole increase the maximum of 24.71,21.60 and 18.88mg/g on the 8th,23th and 23th day,respectively.The soluble sugar and protein have a higher concentration than the other two treatments.The concentration of VFAs of the layered seeding and the sole fermentation reach the highest level on the 15th and 20th day,respectively,are 33.03 mg/g,31.51 mg/g,then falling rapidly and the concentration of layered seeding is lower than the sole.The value of the mixture is 31.30 mg/g on the 20th day,not decrease later and cause acidification.The concentration of ammonia nitrogen are all keep stable relatively after increase gradually,the layered seeding with the lowest level is 2.68±0.33 mg/g.?3?The richness and diversity of bacteria are higher than that of the archaea.Layered seeding can enhance the richness and diversity of bacteria and archaeal,and they increased by prolonging the experience time.however the mixture can only increase that of bacteria.?4?Firmicutes is the dominant bacterial in all digesters.Clostridium shows the absolute predominance.The relative abundance of Clostridium show tendency of first increasing and then decreasing between 43.06%-67.70%,54.62%-76.40%,33.55%-74.68%respectively,and negative correlations with the specific methane yield.Clostridium sensu stricto,Romboutsia showed extremely significant positive correlation with VFAs and SCOD.?5?Euryarchaeota is the dominant archaeal in all digesters.Methanosphaerula?Hydrogenotrophic methanogens,HM?and Methanothrix?acetoclastic methanogens,ACM?show the absolute predominance.HM which the relative abundance higher than 66.93%is the dominant pathway in all digesters.In the late of the sole and the mixture,the relative abundance of ACM archaeal increase from 15.84%and 21.03%to 29.33%and 28.15%,but decrease from 21.03%to 20.86%in the layered seeding.Methanothrix showed significant positive correlation with VFAs.?6?Modified Gompertz model?R²:0.9907-0.9976?has the best fitting degree and the least residual value than first-order kinetic and Cone model for SS-AD.The simulative cumulative methane production and lag phase of the modified Gompertz model are 3.80 mL/g VS·d and10.90 d,all superior to the sole?2.65 mL/g VS·d?26.32 d?and the mixture?1.52 mL/g VS·d?79.52 d?.