Effect Of Cattle Farm Wastewater On Pretreatment And Anaerobic Fermentation Characteristics Of Rice Straw

With the gradual reduction of the storage of fossil energy such as oil and coal,widely distributed biomass resources have gradually entered people’s field of vision.As an important raw material for anaerobic fermentation to produce methane（CH₄）,straw can replace fossil energy to a certain extent.However,in actual production,people often ignore its huge potential.In the process of straw biochemical utilization,the complex structure formed by lignocellulose needs to be destroyed first,so as to improve the utilization efficiency of straw.Straw pretreatment can effectively solve such problems.Cattle farm wastewater has the characteristics of high suspended solids（SS）,high chemical oxygen demand（COD）,and high nitrogen and phosphorus content.Most of the nitrogen in livestock and poultry manure is excreted in the form of organically combined state,about 70%of the nitrogen is in the dissolved state,and most of the dissolved nitrogen exists in the form of ammonium ions（NH₄⁺）.Ammonia is a good straw ammonia pretreatment reagent.It exists in many forms,including liquid ammonia,ammonia water,ammonium carbonate,urea,etc.Therefore,using livestock and poultry breeding wastewater to pretreat straw can not only make full use of wastewater NH₄⁺in and can replace expensive pretreatment reagents.However,the ammonia nitrogen content in the cattle farm wastewater is lower than the ammonia content required for ammoniated pretreatment.Therefore,the large specific surface area of the straw itself and its good adsorption characteristics for water are used to improve the ammonia nitrogen content by filtering the cattle farm wastewater.Nitrogen content is beneficial to achieve better pretreatment effect.In addition,some actinomycetes,fungi and bacteria in livestock manure can hydrolyze lignin under micro-aerobic conditions,but the ammoniated pretreatment is usually carried out under sealed conditions.In view of the above problems,the main research contents and conclusions of this paper are as follows:（1）Filtration test was performed on rice straw as a filter material at 2 mm,5 mm and 8 mm particle size,respectively.The test conditions are:the fill height is 4.50 cm,the filter layer is0.17 g·cm^-3,the ratio of rice straw and the cattle field wastewater is 1:5（w/w）,the filtration time is 10 min.Studies have shown that during the filtration,with the decrease in the particle size of the straw,the higher the ammonia nitrogen adsorption rate of straw against the cattle farm wastewater,the lower the ammonia nitrogen content in the filtrate,the larger the TS and VS,the lower the C/N.When the rice straw particle size is 2 mm,the ammonia nitrogen adsorption rate can reach 33.73%.（2）Six pretreatment methods were screened under the conditions of pretreatment temperature of 30°C,pretreatment time of 10 d and straw particle size of 5 mm,as follows:Cattle farm wastewater soaking seal,cattle farm wastewater soaking semi-sealing,cattle farm wastewater soaking opening;cattle farm wastewater filtration seal,cattle farm wastewater filtration semi-sealing,cattle farm wastewater filtration opening.The results showed that in addition to the opening test group,other treatment methods have good removal effect on the lignocellulose of rice straw,the lignin removal rate is around 60%,the residual rate of cellulose and hemicellulose reaches 83%-87%and 77%-79%,respectively.The ammonia nitrogen concentration of the soaking sealing test group was raised after the pretreatment,and the nitrate nitrogen and dissolved oxygen content showed a decrease in trend,soaking semi-sealing and soaking opening test group liquid component change laws were opposite.The analysis found that it is feasible to realize the ammonia nitrogen pretreatment of rice straw by using the ammonia nitrogen in the wastewater of the cattle farm.（3）Systematic study of the influence of pretreatment temperature（20°C and 30°C）,pretreatment time（4 d,7 d and 10 d）,straw particle diameter（2 mm,5 mm and 8 mm）and pretreatment method（cow farm wastewater soaking seal,cow farm wastewater soaking semi-sealing;cow farm wastewater filter seal,cow farm wastewater filter semi-sealing）on the removal rate of lignin,cellulose and hemicellulose from rice straw,relatively high,low solid content under conditions the law of wastewater pretreated rice straw,explains the mechanism of rice straw pretreatment with cattle farm wastewater.The results showed that the removal rate of rice straw lignocellulose during pretreatment was positively correlated with the pretreatment time and the pretreatment temperature,negatively correlated with the straw particle size.Different pretreatment methods the removal effect of lignocellulose is characterized by superior sealing group,and the soaking group is better than the filtration group.The optimal pretreatment conditions of the 4 pretreatment methods were:pretreatment temperature 30°C,pretreatment time 10 d,the straw particle diameter is 2 mm,the lignin removal rate is 68.08%,65.61%,61.26%and 60.65%;the remaining rate of cellulose is 83%-90%;the remaining rate of hemicellulose is 76%-86%.（4）The dynamic law of the gas production,methane production and VFA content of rice straw pretreated with cattle farm wastewater in the process of mesophilic anaerobic fermentation at 35°C was systematically studied.Elucidating the effect of cattle farm wastewater pretreatment on the gas production characteristics of rice straw anaerobic fermentation.The results showed that the pretreatment of cattle farm wastewater significantly improved the methane production and methane production efficiency of rice straw,and the change in cumulative methane production increased with the increase of the lignin removal rate during the pretreatment process.The maximum cumulative methane production of the four pretreatment methods of cattle farm wastewater soaking and sealing,cattle farm wastewater soaking semi-sealing,cattle farm wastewater filtration sealing and cattle farm wastewater filtering semi-sealing are 7000.09 m L,6800.45 m L,6100.97 m L and 5700.50 m L respectively,which are higher than The control group increased by 81.9%,76.7%,58.5%and 48.1%,respectively,and the methane production efficiency reached 292.62 L·kg^-1VS,287.76 L·kg^-1VS,274.18 L·kg^-1VS and 260.84 L·kg^-1VS,respectively.