Research On A Composite Additive Of Anaerobic Fermentation For Biogas With Metal Salts

Anaerobic digestion techniques are among the most effective ways to deal with biomass waste and domestic organic waste.Anaerobic digestion（AD）technology produces biogas,a clean energy source that people can use.This is accomplished through a series of biochemical reactions involving the digestion of a substrate by anaerobic microorganisms in anaerobic conditions.AD has the dual benefits of protecting the environment while recycling natural resources.China’s biogas projects currently have problems,such as low biogas production,low consumption of substrate,and excessive amounts of unusable residue and slurry.Researching and developing exogenous additives with multiple catalytic properties in the biogas AD process is one way to mitigate these problems.This research first studies the effects of three individual organic exogenous additives on the production of biogas from the anaerobic digestion of cattle dung.The additives are:urea;diammonium phosphate;and citric acid.Next,combinations of these three organic exogenous additives are investigated to determine their effectiveness ratios.Then,different kinds of iron salts,cobalt salts,and nickel salts are incrementally added to the compound organic exogenous additives to study their influence on gas production,chemical oxygen demand reduction,and the fertility of residue.In addition,wheat straw,tree leaves,and corn cobs are used instead of dung to investigate how compound additives with metallic salts affect the anaerobic digestion of different substrates.The influences on biogas production are compared to the results obtained by adding biochar made from wheat straw,leaves,and corn cobs to AD processes using dung as the substrate.According to the results obtained in this research,the following conclusions can be drawn:if 0.3wt%urea,0.3wt%diammonium phosphate,and 0.5wt%citric acid are added to an aerobic digestion system,the system will attain maximum cumulative gas production.There is a 38.9%improvement over the comparison group.The addition of0.6wt%ferric nitrate and 0.005wt%cobalt chloride to the compound,organic exogenous additives further increases gas production to the maximum overall cumulative amount,which is 71.5%higher than that of the comparison group.Chemical oxygen demand reduction is also quite high,at 68.5%.In addition,fertility experiments show:total nitrogen,phosphorous,and potassium content of the residue and slurry are higher than national standards for nutrient content of organic fertilizers（≥5wt%）.So,they could potentially be made into fertilizer.In addition,the compound exogenous additives with metallic salts for biogas AD are also suitable for use in systems that digest wheat straw,tree leaves,and corn cobs.The benefits of the additives are even more pronounced when the above substrates have undergone alkali pre-treatment.Biochar made from the carbonization of biomass waste such as C_{wheat straw},C_leaves,and C_{corn cobs} used as additives in biogas AD systems also have significant stimulatory effects.Overall,the metallic salt-containing,compound,exogenous additives for biogas AD developed in this research are suitable for employing in AD systems using livestock manure,or agricultural/forest waste as substrates in the production of biogas.They simultaneously improve gas production rate,chemical oxygen demand reduction,and the fertility of residues and slurry.The results of this study can serve as a theoretical reference for improving the operational efficiency of biogas AD systems in China.