Measurement Of Heavy Metal In Feed And Faeces Of Pigs And Screening Of Lead And Cadmium-Tolerant Strains Used In Composting

With the development of livestock and poultry production,there are more and more large-scale,intensive farms in our country.These farms provide a large amount of meat and eggs for people,at the same times result in some important social problems.The first one is the feces and urine pollution caused in the production,which is characterized by large quantity and centralized distribution.The second problem is excessive use of metal additives in feed to improve production efficiency and economic benefit.Excessive using metal additives results in heavy metal pollution,which influences environment by ways of land compaction and insect reduction,and particularly endangers human health by their enrichment in crops.However,there are some solutions for these problem.For instance,compost fermentation can turn the feces and urine into useful manure,and heavy metal pollution can be managed by microbial repair.In order to fully understand the content of metals in feed and pig manure of farms in Shandong province,and select suitable strains added into the compost to reduce the bio-availability of heavy metals,in this study,firstly,we collected and measured the mineral content in the 860 feed and faeces samples from 86 large-scale pig farms in 16 districts of Shandong province.Then,we built fermentation models,screened the strains with heavy metal tolerance,and studied their tolerance mechanism to heavy metals.The result showed that the average addition of Fe,Mn,Ca,Zn and Cu conformed to the"Safety use specification for feed additives"(No.1224^th,Ministry of Agriculture Announcement),and only a few pig farms had exceeded the maximum limit value,indicating that most of the complete seeds used in the large-scale farm are in line with national standards.The distribution trend of mineral element residues in pig manure was consistent with that in feed,in which there is a significant correlation of the content of Zn and Cu between the feed and faeces.Our results show that the excessive addition of mineral elements in feed is the main reason for the increase of Zn and Cu element residues in pig manure.The screening of lead?Pb?and cadmium?Cd?-tolerant strains showed that we successfully screened two strains with tolerance to Pb and Cd from pig manure compost samples,numbered C1 and T2 respectively.By measures of their morphological characteristics,routine physiological determination and homologous ratio analysis of 16S rDNA sequences,the two strains were initially identified as Cedecea neteri and Bacillus cereus,respectively.And further research of the growth conditions of C1 and T2 strains indicated that,the optimum pH of two strains was 7,the optimum growth temperature was 37?,and the optimum NaCl concentrations were 0.5% and 0.5-2%,respectively.The removal rates of the two strains of PB and CD both were above 50%.This study not only provides data for a comprehensive understanding of the content of heavy metals in feed and pig manure in farms of Shandong province,but also lays foundation for reducing the bio-availability of heavy metals in the composting process of livestock and poultry manure using tolerant microorganisms.