| China produces more than 200 million tons of agricultural waste each year,of which corn stalks account for about 30%.The use of corn stalks as raw materials for anaerobic fermentation can obtain biogas and biogas fertilizer,which is of great significance to make up for energy shortage,environmental protection and ecological restoration..In the anaerobic fermentation process,due to the poor sedimentation of corn stalk itself,it is easy to float to form a scum layer to affect the methanogenic efficiency.Whether the scum layer depends mainly on the water absorption of the corn stalk,according to the composition and structural characteristics of the straw,the naturally dried corn stalk has sedimentation if it absorbs enough water.At present,many studies have proved that pretreatment of corn stover can affect its lignocellulosic state,and the destruction of dense structure has a certain influence on its sedimentation.In order to further explore the effects of different pretreatment methods on the scum layer and gas production of straw biogas production process,two kinds of industrially easy to implement corn stalk pretreatment methods: aerobic hydrolysis and straw extrusion molding technology were adopted.After the treatment,the changes of lignocellulose in the substrate,the state of scum layer in the anaerobic fermentation stage and the results of gas production were analyzed.The main results and conclusions were as follows:(1)The aerobic hydrolysis of corn stover can reduce the volume ratio of scum layer in anaerobic fermentation stage and increase the yield of VS.Orthogonal test and comprehensive weighted score were used to determine the optimal combination conditions of aerobic hydrolysis for corn stover: 45 °C hydrolysis temperature,2h aeration 10 min aeration mode and 12 h hydrolysis time.Compared with the direct anaerobic fermentation of corn stover,the methanogenic rate of the corn stalk VS under the combined conditions was 264.27 m L/g,which was 73.09% higher;the initial scum layer volume ratio was 18.22%,which was a relative decrease of 35.18%..(2)Applying high temperature and high pressure to corn stover during extrusion process,destroying the microstructure and porosity of corn stover,improving the water absorption and sedimentation of corn stover,and reducing the volume ratio of scum in the initial stage of anaerobic fermentation.And to some extent increased the degradation rate of lignocellulose.Compared with the initial anaerobic fermentation,the initial scum layer volume ratio of the anaerobic fermentation control group is reduced by 50% compared with the initial scum layer volume ratio of the anaerobic fermentation,which is lower than the initial scum layer of the aerobic hydrolysis treatment group under the optimal conditions.The volume ratio was reduced by 30% and the scum layer disappeared at 21 d.The methanogenic rates of TS and VS were 199.71 m L/g and 246.55 m L/g,which were 58.32% and48.46% higher than those of the direct fermentation control group.(3)Extrusion of granular corn stover and aerobic hydrolysis can further reduce the volume ratio of the scum layer in the initial stage of anaerobic fermentation,and the disappearance time of the scum layer is greatly reduced,and the methane yield is also improved.Orthogonal test and comprehensive weighted scores were used to determine the most suitable combination conditions for aerobic hydrolysis of corn stalk extrusion pellets: 40 °C hydrolysis temperature,1 h aeration 10 min aeration and 4 h hydrolysis time.Compared with the direct anaerobic fermentation of corn stalk extrusion granules,the VS methanogenic rate under this condition was 274.32 m L/g,which was 11.26% higher;the initial scum layer volume ratio was 11.34%,and the relative reduction was 23.17%;The time required for the layer to disappear is 11.73 d,which is a relative shortening of 44.54%.Compared with the optimal conditions for aerobic hydrolysis of corn stover,the required hydrolysis temperature and hydrolysis time are reduced,but the aeration rate is improved. |
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