Study On The Effect Of Trace Co And Ni On The Anaerobic Digestion Of Straw

For the solid organic waste containing much fibrin, the efficiency of anaerobic digestion and the gas yield are very low. The effects of trace metals and chemical pretreatments on the process of anaerobic digestion for straw and the mathematical model have been studied, and the biogas yield, the methane content, VS(Volatile Solid) removal ratio and COD(Chemical Oxygen Demand) reduce ratio have been analyzed as indexs. The results showed that chemical pretreatments and adding trace Co, Ni were efficient ways to improve the anaerobic digestion of straw.The biogas yield increased respectively by 39%, 74.5% and 115% as Co, Ni or Co+Ni was added in digestion system. The methane content increased respectively to 50%, 52.2% and 62.5% from 44.9%, VS removal ratio improved respectively to 46.2%, 47.6% and 53.2%from 39.3%, and COD reduce ratio increased respectively to 56.9%, 57% and 58.9% from 42.4%. It indicated that adding the mixed trace metals of Co and Ni is an effective approache to improve the anaerobic digestion efficiency and biogass yield.The biogas yield of anaerobic digestion for straw was highly increased by pretreatments of dilute HCl solutions. All of the indexs(the biogas yield, the methane content, VS removal ratio and COD reduce ratio) increased with the concentration of dilute HCl solutions(4%, 8% and 12%). The optimum biogas yield of straw anaerobic digestion could be made by pretreatment of 12% dilute HCl solution. The biogas yield increased by 241%, the methane content increased by 11.7%, VS removal ratio improved by 13.7%, and COD reduce ratio increased by 44%.It's obviously that pretreatments of dilute H2SO4 solutions could increase the methane content and COD reduce ratio of digestion system remarkably, and the biogas yield and VS removal ratio increased, too. The dilute H2SO4 solutions in different concentration were used to pretreating the straw, and the experimental results showed that H2SO4 solution of 1.5% was a deal dosage. The methane content increased to 58.4%, and COD reduce ratio increased to 72.76%.The 12% dilute HCl solution or the 1.5% dilute H2SO4 solution was used to pretreating the straw before adding mixed trace metals of Co and Ni to the anaerobic digestion system, and more biogas yield and methane content could be produced, comparing with adding the mixture of Co and Ni to the system only. Pretreating the straw with 12% dilute HCl solution before adding mixed trace metals to the digestion system, the methane content increased to 4.6%. The anaerobic digestion capability of straw attained the best effect with a combined method of pretreating the straw with1.5% dilute H₂SO₄ solution then adding mixture of Co and Ni to the digestion system, and the biogas yield rate increased to 30.3%, the methane content increased to 8.1%.The relationship between gas yield(volume) and digestion time of anaerobic digestion for straw in different condition have been analyzed by mathematical model, and got a non-linear regression equation. A 6-th degree equation in one variable, which can be used as describing characteristics of anaerobic digestion process, have been obtained.