Reaserch Of Electrochemical And Chemical Pretreatment Of Straw For Anaerobic Fermentation Production Of Biogas

Straw can be used as a raw material for biomass production in anaerobic fermentation project.As the structure of the lignocellulose in the straw is particularly difficult to be used by microorganisms or enzymes,it often results in less production and longer cycle.Appropriate pretreatment of straw can improve its anaerobic digestion gas production performance and shorten the gas generation cycle.At present,the common methods such as steam blasting,microwave and other physical methods require high energy consumption.The preparation of acid and alkali used in chemical method is more demanding to the equipment.The biological method is the most moderate and energy saving and environmental protection,but the pretreatment process is very time consuming.Therefore,it is the key to find a pretreatment method which can shorten the fermentation cycle of straw and improve the gas production.Some studies have shown that the electrochemical oxidation can effectively destroy the structure of lignocellulose.In this paper,electrochemical oxygen cathodic reduction method was used to prepare the electrolyte.The optimum conditions for the anaerobic fermentation of straw were studied.Finally,the fermentation performance of straw under different pretreatment conditions was studied.The mechanism of different pretreatment on straw degradation was also discussed.Firstly,the temperature,time and water content of the pretreatment of electrolyte and chemical solution were optimized respectively.The current intensity,electrolysis time and temperature of the pretreatment were optimized.The optimum pretreatment conditions for the final determination of the electrolyte were as follows:50 ?,6 times water,3 days.The optimum pretreatment conditions for the chemical solution were as follows:35 ?,6 times water,3 days.The optimum conditions for the pretreatment of electrolysis were:0.15 A,35 ?,5 h.The effects of different methods on the anaerobic fermentation of straw after optimum pretreatment were studied experimentally.The results showed that the highest peak of the straw gas produced by the electrochemical method(electrolytic method and electrolysis method)was 5 to 12 days earlier than the chemical method(chemical solution and NaOH),the gas generation cycle was shortened by more than 5 days,T80 was shortened by 13 to 16 days,and the cumulative gas production reached 295 mL/gTS,which was about 18%higher than that of the chemical pretreatment group(chemical solution:261 mL/gTS,NaOH:249 mL/gTS).TS and VS removal rates were 21%and 18%higher than those of NaOH pretreatment.The cumulative methane yield of straw anaerobic fermentation after electrochemical method and chemical liquid pretreatment was 6%?13%higher than that of chemicial pretreatment groups.The results show that the pretreatment of electrochemical method can effectively improve the gas production and methane content of anaerobic fermentation of straw and shorten the fermentation cycle to a great extent.Finally,the straw composition before and after pretreatment was analyzed,and the mechanism of different pretreatment on the degradation of straw was studied by electron microscopy and X-ray diffraction.The analysis of the content of lignocellulose in the straw before and after pretreatment showed that the content of hemicellulose decreased and the content of cellulose decreased after the pretreatment of electrolysis and electrolytic solution.SEM images show that the surface texture of the straw pretreated by electrolytes and electrolysis is the largest,and the cellulose structure is exposed.XRD data showed that the crystallinity of straw was 50.4%and 51.3%,which was significantly higher than that of chemical pretreatment straw(45.2%?45.9%)after pretreatment with electrolytic method and electrolysis method,which indicated that the damage of cellulose in nonamorophous area was more easily by enzyme or microbial degradation.