Effect Of Passivating Agent On The Reduction Of Cu And Zn In Anaerobic Fermentation Of Pig Manure/Straw

With the widespread application of feed additives,animal manure contains a large amount of heavy metals such as Cu,Zn,etc.The long-term application of manure,which uses pig manure as raw material,will lead to the accumulation of heavy metals in the soil,result in soil pollution and affecting human health.A large number of studies have shown that the total amount of heavy metals can't effectively reflect the damage of heavy metals to plants and the environmental.The bio-availability of heavy metals depends more on its form existence in the environment.In order to explore the form changes of heavy metals in the anaerobic fermentation process and reveal the mechanism of the passivator of heavy metals,study the effect of adding deactivators on the bio-availability of heavy metals,In this paper,pig manure and corn stalk are used as raw materials,heavy metals Cu and Zn as the research object,and using different kinds and ratios of passivator.The inoculum volume is 30%,TS is 8%,the temperature is 35°C,carbon and nitrogen at a ratio of 24,pH of 7 and 60 day fermentation.In order to explore the binding mechanism of heavy metals Cu,Zn and organic matter during the anaerobic fermentation process,analyzing the heavy metal forms and organic carbon contents through the improved BCR extraction method and H₂O,KCl,Na₄P₂O₇,NaOH and HNO₃fractional extraction methods in before and after fermentation and during fermentation.Optimizing the process conditions based on the reduction of Cu and Zn bioavailability to provide a theoretical basis and technical support for the harmless and resourceful treatment of livestock and poultry manure.The main research conclusions obtained through the experimental study are as follows:?1?After anaerobic fermentation of pig manure/straw mixture,addition of passivator will reduce the content of Cu in the biogas residue.The addition of 7.5%phosphate rock has the best reduction effect.The content of Cu in the biogas slurry was the lowest after adding 5.0%phosphate rock,which was 4.27mg/kg.Adding sepiolite will reduce the distribution rate of heavy metal Cu in the biogas residue.The addition of passivator will reduce the content and distribution rate of heavy metal Zn in the biogas residue,and increase the Zn content and distribution rate in the biogas slurry.The content of Zn in the biogas residues in the phosphorus ore powder with a proportion of 7.5%was the lowest and the distribution rate was430.52 mg/kg and 83.72%.?2?The addition of sepiolite can reduce the content of exchangeable and reducible Cu in the biogas residue after fermentation,and increase the oxidizable and residual Cu content.The addition of phosphate rock powder will reduce the exchangeable,reducible and oxidizable Cu contents of the biogas residue and increase the residual Cu content.The higher the proportion of passivating agent added,the lower the content of Cu in the exchangeable,reducible and residual forms of biogas residue,and the higher the content of oxidizable Cu.From the available state,the content of available Cu in the treatment of sepiolite addition is lower than that of added phosphate rock.The addition of sepiolite can effectively reduce the content of available Cu,and the addition of 7.7%results in the best reduction.From the steady state,adding sepiolite can increase the steady-state Cu content,and the addition ratio of 7.5%is the best.From the perspective of bioavailability index,the addition of sepiolite will reduce the bioavailability index of heavy metals Cu in biogas residue.The effect of adding7.5%is the best.Adding phosphate rock powder will increase the bioavailability index of heavy metals Cu in biogas residue.Compared to the control treatment,the addition of sepiolite reduces the four forms of Zn in the biogas residue.From the available state,adding 5.0%of phosphate rock powder is more conducive to reducing the available Zn content in the biogas residue.?3?The content of organic matter in the biogas residue during the fermentation process showed a rapid decrease in the early and middle stages,and a slowly decreasing trend in the later period.After adding the deactivating agent,the content of organic matter in the biogas residue decreased.The forms of Cu and Zn in biogas residues are mainly organic complexes,and the proportions are between 38-45%and 80-85%.The distribution rates of Cu and Zn in water-soluble and exchangeable forms will gradually decrease with the progress of the fermentation process,and the mineral and residue state will gradually increase.Addition of passivator will further increase this trend,the effect of sepiolite More obvious.Most of the Cu and Zn in biogas residue are mainly combined with FA.With the progress of fermentation,HA content increased,FA content decreased,and HA/FA also gradually increased.The content of HA-Cu gradually increased with the progress of fermentation,but the HA-Zn content did not change significantly.The addition of sepiolite and phosphate rock powder promotes the formation of HA-Cu,thereby enhancing the stability of Cu in humus,and the addition of rock phosphate powder is superior to sepiolite.Through the analysis of the correlation between the steady state Cu,Zn content and humus content in the biogas residue,the content of humus in the biogas residue after adding sepiolite was positively correlated with the steady state Cu content at 0.01 level?r=0.9597,P=0.01,n=7?;The content of humus in the biogas residue after addition of phosphate rock powder was significantly positively correlated with the content of Zn in 0.01 level?r=0.9642,P=0.05,n=7?.