| In recent years,with the application of feed breeding method,the feed added some heavy metal elements,resulting in livestock and poultry manure heavy metal residual pollution intensified.The heavy metals in livestock and poultry manure have become bottlenecks restricting their resources.Biogas anaerobic fermentation is an effective way to recycle livestock and poultry waste.In this paper,heavy metal is used as the object of study,pig manure is anaerobic fermentation raw material.The test factors are different types of passivating agents(fly ash,diatomaceous earth,activated carbon),different addition ratio(2.5%?5%?7.5%)and different temperature(25??30??35?).By orthogonal test,the heavy metal morphology results are analyzed by BCR extraction method.Explore the order and the optimal level of factors and the best process conditions,which the effects of three different passivators on the anaerobic fermentation gas production,methane content and heavy metal morphological changes,in order to provide scientific basis for the safe and rational application of biogas slurry.Through the above experimental study,the following main conclusions are drawn:1?Test results found that,Compared with the blank group test group,added 5%activated carbon passivation agent,the temperature of 35? fermentation which has the highest gas production.Through the analysis of the variance,the factors affecting the gas production are the type of passivator,the temperature and the addition ratio of the passivating agent.Temperature had a significant effect on the gas production,passivating agents and addition ratio had no significant effect.The optimal scheme is which the temperature is 35?,the passivating agent is fly ash and the addition ratio of the passivating agent is 2.5%.The total methane content of the test group is about 40%which relatively stable.Conditions of adding 5%activated carbon passivation agent and 30?,methane content is the highest,reaching 41.2%.Through the analysis of the variance,the factors of the primary and secondary order that affect the methane content are the passivation agent type,temperature and passivation agent addition ratio.Analysis found that passivation agent type had a significant effect on the methane content,and changes in the level of addition ratio and temperature almost no effect on the test results.The optimal solution is that the passive agent is activated carbon,the temperature is 35?,the addition ratio of the passivating agent is 2.5%.2?Before the experiment,84.42%of heavy metal Zn,83.75%of heavy metal Cr,88.49%of As are present in pig manure.After the fermentation is finished,the distribution of heavy metal Zn and Cr content in the biogas residue is increased,accounting for 86.49%?89.91%and 87.33%?91.72%.The distribution rate of As content decreased to 78.18%?83.18%.The distribution rates of heavy metals Zn,Cr and As in biogas slurry before fermentation are 15.58%,16.25%and 11.51%respectively.After the end of anaerobic fermentation of pig manure,the proportion of heavy metals Zn and Cr in biogas slurry was decreased,the distribution rate dropped to 10.09%?13.51%and 8.28%?12.67%.The content of As in the biogas slurry was increased to 16.82%?21.82%.3?The heavy metals Zn in pig manure before fermentation is mainly in exchangeable state(45.26%)and recoverable state(21.89%),heavy metals Cr and As mainly exist in the residual state,the proportion reached 66.15%,62.61%.After the anaerobic fermentation,the biogas residue of adding passivation,the distribution of different forms of Zn showed that:the residual fraction is increased,which is larger than that of the blank group;The exchange rate of exchangeable fraction is still high;There are varying degrees of increase or decrease of easily reducible fraction and oxidizable fraction in the different treatments.Cr and As still exist in the residual state,the proportion increased,which is larger than that of each blank group.The exchangeable?oxidizable and the reduce state are decreased,and the proportion after fermentation was lower than that of the blank4?The deactivation effect of heavy metal Zn effective fraction in the condition of adding 7.5%fly ash and 35? is the best,reaching 37.57%.The best passivation effect of test group is the group of adding 5%activated carbon and 35? conditions,reaching 66.69%.The best passivation effect of test group is the group of adding 7.5%activated carbon and 25 ?conditions,reaching 61.46%.Through the analysis of the variance,the factors of primary and secondary order that affect the interchangeability of heavy metal Zn are the types of passivating agents,the temperature and the addition ratio of passivating agents.The types of passivating agents and temperature have a significant effect,and the effect of addition ratio is not significant,The optimal level is that the passivation agent is fly ash,the temperature is 25? and the addition ratio is 2.5%.The addition of the passivating agent in the group of biogas residue,effective passivation effect of heavy metal Cr is more than 40%.Through the analysis of the variance,the factors of primary and secondary order that affect the effective of heavy metal Cr are the type of the passivating agent,the temperature and its addition ratio.The types of passivating agents have a significant effect,and the effect of addition ratio and temperature are not significant.The optimal level is that the passivation type is activated carbon,the temperature is 25?,and passivation agent addition ratio is 2.5%.After the end of test,the addition of the passivating agent in the group of biogas residue,effective passivation effect of As is more than 40%.Through the analysis of the variance,the factors of primary and secondary order that affect the effective passivation of As are the type and addition ratio of the passivating agent and the temperature.The types of passivating agents have a significant effect,and the effect of addition ratio and temperature are not significant.The optimal level is that the passivation type is activated carbon,the temperature is 25?,and passivation agent addition ratio is 2.5%. |
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