Effects Of Pretreatment And Cr³⁺ On Mesophilic Anaerobic Digestion Of Straw

Crop straw is an important part of biomass resource, which is widely distributed around the countryside of China. However, most of biomass materials are utilized in the form of burning, and the dust produced in this process does great harm to the environment. Therefore, anaerobic digestion is studied as a significant technique of straw degradation, which is based on the digestion of compound bacteria and converts biomass such as corn stover to organic fertilizer and biogas, but lignocellulose gives the plant structural support, impermeability, and resistance against microbial attack and oxidative stress, which makes the degradation of crop straw very tough. At the same time, dosage of heavy metal ions has a great influence on biogas production.Mesophilic anaerobic digestion system was used to degrade corn stover in this article. Wet state sodium hydroxide was advanced to pretreat corn stover at 85-90℃ for enhancing biogas production and ecological microoganisms(EM) acts as inoculum. The results showed that NaOH pretreatment at high temperature for 1h causes huge destruction of corn stover’s chemical structure. When the mass of corn stover was 30g, the cumulative biogas production was 1225mL and the average biogas production was 40.83mL/g.NaOH, KOH, Ca(OH)2 have significantly destructive actions to the chemical structure of corn stover, and alkali pretreatment was appropriate for mesophilic anaerobic digestion system. NaOH, KOH, Ca(OH)2, Al(OH)3 were adopted as reagent of alkali pretreatment, then corn stover was pretreated for 5 days at room temperature(17℃) in batch anaerobic digester whose volume was 250mL and then was digested by white rot fungi biogas slurry. When the mass of corn stover was 15g, the results showed that com stover pretreated by Al(OH)3 has the largest cumulative biogas production(3885mL), the longest running time was 50d for the KOH digester, the device for NaOH pretreatment gains the largest daily biogas production(235mL).The addition of Pb2+ and Cr3+ restrained biogas production of mesophilic anaerobic digestion system strongly. The experiment of effect of Cr3+ and Pb2+ on mesophilic anaerobic digestion was carried out by NaOH pretreatment and 100mL white rot fungi biogas slurry. Doses of 0,50,100,150,200,250,300mg CrCl3 were added to the digestion system and the addition of Pb(NO3)2 were 10,20,30,40,50, 100,150mg. The biogas production order was 0mg(3540mL)> 150mg(3220mL)> 200mg(2900mL)>50mg(2785)> 100mg(2370mL). There was no biogas producing in devices of Cr3+(250mg) and Cr3+(300mg). At the same time, none of biogas was produced in the devices which contained quantitative Pb(NO3)2. Above all, the results illustrated that high concentration of Cr3+ and low addition of Pb2+ led the fungus to death.