| Due to the high content of heavy metals in the feces,the products of anaerobic fermentation also contain a large amount of corresponding heavy metals.At home and abroad,there are relatively few studies on the treatment of heavy metals in biogas fermentation products.The anaerobic fermentation produces biogas,which not only can produce clean energy,but also can deal with a large amount of livestock and poultry manure produced by livestock and poultry breeding,and reduce the pollution caused by livestock and poultry manure.It is extremely important for environmental protection.In this experiment,fresh pig manure is used as the fermentation raw material,and two different kinds of nutritive passivators(phosphorus ore,boron mud)and different addition ratios(2.5%,5.0%,7.5%)are added.Under suitable fermentation conditions,An anaerobic fermentation test was carried out.The effects of nutritive passivation agent on the content and distribution of heavy metals Cr and Cd in anaerobic fermentation products,the change of Cr and Cd morphology in biogas residue and the passivation effect were studied.The effect of adding nutritive passivation agent on biogas production by fermentation was studied.influences.It is hoped that through this paper,new research ideas will be provided to improve the environmental performance of anaerobic fermentation and enhance the harmless treatment of livestock manure.The main conclusions of this paper are as follows:(1)After the fermentation,the total amount of heavy metal Cr in each test treatment group was lower than the maximum limit of Cr in organic fertilizers by international authoritative organizations,and the effect of Cr disaster reduction treatment was remarkable.The distribution of Cr in the biogas residue in the treatment group with phosphate rock added was higher than that in the test group with added boron sludge.After the fermentation,Cr was mainly in the residual state,and the addition ratio of the passivating agent had a significant effect on the content of oxidizable Cr.The addition of passivating agent can reduce the content of heavy metal Cr in the biogas residue,and the content decreases with the increase of the proportion of passivating agent.The treatment effect of adding 7.5% boron mud is the best,and the addition ratio of passivating agent is the same.The distribution rate of the effective state of heavy metal Cr in biogas residue has a significant effect;the addition of passivating agent can promote the transition of the effective Cr to the steady state.(2)After the fermentation,the total amount of heavy metal Cd in each test treatment group was lower than the highest limit of Cd in organic fertilizers by international authorities,and the effect of Cd on disaster reduction was significant.The distribution rate of Cd in the biogas residue in the treatment group with phosphate rock increased with the increase of the proportion of phosphate rock powder,and decreased with the increase of the proportion of boron mud.After the fermentation,the Cd was mainly in the residual state,blunt.The addition ratio of the chemical agent has a significant effect on the Cd content of the heavy metal in the residual state;the addition of the passivating agent can reduce the content of the effective state of the heavy metal Cd in the biogas residue,and the content decreases with the increase of the proportion of the passivating agent,and the addition of the boron mud treatment group The effective content is lower than that of the phosphate rock treatment groupin the same proportion.The addition of passivating agent can reduce the content of heavy metal Cd in the biogas residue,and the content of the 7.5% boron mud treatment group is the lowest.(3)The treatment group with nutritive passivation agent has obvious passivation effect on heavy metals Cr and Cd.The passivation effect of two nutritive passivators on heavy metals Cr and Cd is more than 30%,and the passivation effect is related to the passivation agent.The increase in the proportion increases and increases.Among them,for heavy metal Cr,the best choice for passivation effect is to add 7.5% boron mud treatment group,the passivation effect reaches 63.09%;for heavy metal Cd,the best choice for passivation effect is to add 7.5%boron mud treatment group.The passivation effect reaches 84.25%.The passivation effect of the two passivating agents on Cd is better than Cr.The addition ratio of the nutritive type passivation agent has a significant influence on the passivation effect of the heavy metal Cr,the type and addition ratio of nutritive passivation agent have a significant effect on the passivation effect of heavy metal Cd..(4)Compared with the CK group,the addition of nutritive passivation agent will increase the yield of biogas during anaerobic fermentation,increase the average content of methane,and have a good effect on gas production.In the treatment group with phosphate rock powder added,the total gas production increased with the increase of the proportion of phosphate rock powder,and the gas production rate of treatment 3(adding 7.5% phosphate rock)was0.35m3/(d·m3).The average content of methane was the highest,reaching 45.21%.In the treatment group with boron sludge,the total gas production was the highest(treatment 5.0%boron sludge),and the gas production rate was 0.41m3/(d·m3).Under this condition,the average methane content is the highest,reaching 47.85%.Under the same addition ratio,the total gas production and the average methane content of the added boron mud are higher,indicating that the boron mud has a greater effect on the biogas production by anaerobic fermentation than the two nutrient passivators.In summary,the addition of nutritive passivation agent will increase the passivation effect of heavy metals Cr and Cd.The passivation effect of boron mud on heavy metals Cr and Cd is better than that of phosphate rock powder;the proportion of nutrient-type passivating agent is increased for pigs.The increase of biogas production and average methane content in anaerobic fermentation of feces has a promoting effect,and the promotion effect of boron mud is better.Under the conditions of this experiment,increasing the proportion of nutrient-type passivating agent is more conducive to the comprehensive performance of nutritive passivating agent in both heavy metal passivation performance and anaerobic fermentation gas production performance. |
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