| Corn stover are a large number agricultural by-product that accompanies the corn harvest.After harvest,the stover will become dry and yellow due to dehydration,and the rate of natural decay is slow.Therefore,the stover is often returned to the field through incineration,which not only causes waste,but also pollutes the environment.Anaerobic fermentation technology can simultaneously realize the preparation of clean gas fuel and pollutant reduction.However,due to the recalcitrant internal structure,the anaerobic fermentation conversion rate is slow and the gas production efficiency is poor.Therefore,pretreatment is an effective method considered to improve its anaerobic fermentation performance.The output of corn stover in the low-cold regions of northern my country accounts for 70%of the total output of the country.Therefore,the study of high-efficiency pretreatment methods at low temperatures can provide support for solving the problem of stover resource utilization in the north.Based on the natural conditions of autumn and winter when corn is harvested in northern China,this paper studies the effects of NaOH pretreatment of corn stover at low,medium and high temperatures in order to achieve pretreatment in natural environments and improve the anaerobic fermentation performance of stover-like lignocellulosic materials.The main research contents and results are as follows:Using corn stover as raw material,the effect of NaOH pretreatment on raw material structure and gas production performance at medium/high temperature was studied.The experimental results show that NaOH pretreatment has a significant effect on the lignin composition and the mass fraction of N element in the raw materials at medium/high temperature.Among them,the removal rate of lignin is 1.5%NaOH,70?,treatment for 7 h,and solid-liquid ratio of 1:15.It can reach up to 80.98%,and the N element removal rate can reach up to 100%.The optimized pretreatment conditions of response surface experiments were 2.5%NaOH,30?,treatment for 12 h,and solid-liquid ratio of 1:10.Under the optimized conditions,the methane production rate was 314.40 mL/g VS,which was 102.10%higher than that of untreated corn stover.Combined with the climatic conditions during the storage of stover in the north,the effects of freeze-thaw combination on the raw material structure and anaerobic fermentation performance after NaOH pretreatment were studied.The experimental results show that only from the difference of pretreatment additives,alkaline freeze-thaw pretreatment>water freeze-thaw pretreatment>freeze-thaw pretreatment,the process parameters are 2.5%NaOH concentration,solid-to-liquid ratio 1:4,4 times freezing During the melting cycle,the removal rate of lignin in the raw material can reach 67.76%.At the same time,the surface of the raw material has irregular pits due to the formation of ice crystals and local high concentration of NaOH.The methane production rate of samples pretreated by alkali freeze-thaw can reach 326.83 mL/g VS,which was 43.77%higher than that of the freezing-thawing treatment without added group.Based on the temperature conditions of northern stover stored in winter,the effect of freezing on the sample structure and anaerobic fermentation performance after NaOH pretreatment was studied.SEM,XRD and FTIR analysis showed that the surface of the raw material appeared alkali-etched and frozen-fractured structure after freezing treatment,and the crystallinity showed a trend of first rising and then decreasing.At the same time,the H-O bond inside the raw material was broken after pretreatment.The experimental results show that the pretreatment of freezing alkali>the pretreatment of chilled water>the pretreatment group without addition.The 30-day freezing pretreatment process parameters are 2.5%NaOH concentration,solid-liquid ratio 1:4,and freezing treatment at-20? for 30 days.At this time,the lignin removal rate in the sample can reach 16.85%,and the raw material methane production rate can reach 304.10 mL/g VS,an increase of 80.90%compared with the freezing treatment group without added raw materials.On the basis of the above research,using response surface optimization conditions of 2.5%NaOH,30?,treatment for 12 h,solid-to-liquid ratio of 1:10,the stover is used as raw material,and the semi-continuous feeding and discharging method is adopted to optimize the process conditions and investigate the Operational stability of oxygen fermentation process.The experimental results show that the system has the best operating stability when the alkali-treated samples are not washed with water and the reflux process is used;the operating performance of the other experimental groups is in order of washing alkali-treated samples+reflux experimental group>water-washed alkali treatment+non-reflux experimental group>Unwashed alkali treatment+non-reflux experimental group>raw material+reflux experimental group>raw material+non-reflux experimental group.When the alkali-treated sample is not washed with water,and when the reflux process is used,the maximum daily methane production rate of the sample is 375.58 mL/g VS,the cell volume gas production rate is(0.46±0.09)L/L/d,the pH value of the fermentation broth is 7.26-7.49,and the final content of VFA It is acetic acid 4105.60 mg/L and propionic acid 455.56 mg/L.This article uses the typical northern agricultural crop waste corn stover as raw materials,takes raw material gas production performance and system operation stability as indicators,and combines the northern low temperature climate conditions to optimize the NaOH pretreatment and anaerobic fermentation operating process conditions,in order to increase raw material gas production Performance and improving the stability of system operation provide the basis for preliminary research. |
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