Security Risk Analysis on the Nutrients and Heavy Metals of Biogas Slurry in Agricultural Application

[Objective] This study was to provide scientific basis for the security application of biogas slurry in agriculture through the analysis on the security risk of nutrients and heavy metals of biogas slurry in agricultural application.[Method] The components of the slurry produced by the anaerobic digestion of straws and manures were systematically analyzed.Different types of biogas slurry with different concentrations were used to conduct the germination test.[Result] The types and proportions of raw materials,and alkali pretreatment affected the compositions and nature of the biogas slurry.Alkali pretreatment could reduce the contents of heavy metals and improved the contents of nitrogen,phosphorous,organic matter and available components.The contents of heavy metals in the biogas slurry were as follows: Cd of 8.76 μg/kg,Cr of 52 μg/kg,Pb of 210 μg/kg,Hg of 0.512 μg/kg,As of 140 μg/kg,and the contents of Cu and Zn were the highest among the heavy metals,respectively,279 μg/kg and 680 μg/kg.All the contents were under the limit standards of the urban wastes for agricultural use.The germination tests of the seeds verified that the slurry with the concentration of lower than 5% could accelerate the germination,while the salt stress could inhibit the growth of seedlings in the slurry.[Conclusion] When the dung are used as the raw materials for fermentation,appropriate control should be conducted on the feeding proportion or the heavy metals should be pre-removed;when the slurry is used as the liquid fertilizer to apply in the farmland,the dilution or desalting treatment should be conducted at first.