Enzyme Activities During Composting Process In Addition Of Attapulgite

The heavy metals in livestock manure make its contamination problems much more complicated. How to eliminate the pollution of heavy metals during the process of livestock manure composting has become an urgent problem to be solved. The materials of composting in this paper were chicken manure and raw attapulgite clay from banqiao town, linze, Gansu. Six treatments were set. The chicken manure and the attapulgite clay were mixed together with different appending proportion to start aerobic composting. Except for the CK without attapulgite, the proportions of attapulgite to chicken manure of other treatments were A3(3:20), A6(6:20), A9(9:20), A12(12:20) and A15(15:20), respectively. During the composting,the activity of invertase, urease, protease, polyphenol oxidase and catalase of six treatments on different time(the first, fourth, twelfth, twentieth, twenty-fifth and thirty-second day) was assayed. Depending on the physicochemical characteristics of the compost samples and the distribution of heavy metal(Zn, Cu, Cr, Ni) speciation of BCR sequential extraction of compost, the activity variation of enzymes and the correlations between enzyme activity and the other factors were analysed.The main conclusions are as follows:(1) The addition of attapulgite in the composting of chicken manure did not change the process of composting obviously, the enzyme activity of five different treatments had the same variation trends with the CK, and they had synchronous composting process. During the whole composting time, the activity of invertase decreased slightly first and then increased speedily and then decreased gradually until the compost finished. The activity of urease increased first and then decreased quickly and leveled off at the end of compost. The activity of protease had a trend of increase in fluctuation. The activity of polyphenol oxidase increased first and then decreased and then increased again and then decreased again, which resulted in two different degrees of peak values. While the activity of catalase decreased gradually with the proceeding of composting.(2) The influences of different appending proportion of attapulgite in composting on different enzymes were also different. The invertase activity of treatments A9, A12 and A15 were higher than the other treatments. The urease activity of six treatments presented a sequence of CK > A3 > A6 > A12 > A9 > A15. The treatments A6, A9 and A12 had higher protease activity than the other ones. As for the polyphenol oxidase activity, the CK performed the highest polyphenol oxidase activity among the six treatments, and then it came A3, A9 and A6. However, the catalase activity of six treatments performed a sequence as A15 > A12 > A9 > A6 > A3 > CK. Relatively speaking, treatment A9 exhibited higher enzyme acytivities than the others, and had a better composting results.(3) The correlations between the five enzymes were as follows: the protease activity and the catalase activity had a significantly negative correlation(p<0.05). There was significantly positive correlation between urease activity and polyphenol oxidase activity(p<0.05). Besides, the protease activity had a negative correlation with the polyphenol oxidase activity, and the invertase activity also had a negative correlation with polyphenol oxidase activity, and there was a positive correlation between polyphenol oxidase activity and the catalase activity, while the above three relationships were not significant(p>0.05).(4) The correlations between the enzymes and the physicochemical characteristics were as follows: the five enzymes of the six treatments all presented no significant correlations with the temperature(p>0.05). The protease activities of six treatments all shared a weak negative correlation with the pH. There were significantly negative correlations between catalase activity and the electrical conductivity(p<0.05). Besides, there were also negative correlations between urease, polyphenol oxidase activity and the electrical conductivity, while the protease activity had a positive correlation with the electrical conductivity. As for the organic matter content, the catalase activity had a significantly positive correlation with the organic matter content(p<0.01), while the protease activity presented significantly negative correlation with the organic matter content(p<0.05). Besides, there was a negative correlation between the invertase activity and organic matter content, and the urease activity and polyphenol oxidase activity all had positive correlations with the organic matter content.(5) The correlations between enzymes and the heavy metal speciation of BCR sequential extraction were as follows: the response of protease and catalase to heavy metals(Zn, Cu, Cr, Ni) were much more sensitive than the other enzymes, and this two enzymes had more significant correlations with the heavy metal speciation. While the correlations between the other enzymes and heavy metal speciation were not definite. Besides, the two above enzymes(protease and catalase) had the most significant correlations with Zn among the four kinds of heavy metals. What’s more, the correlations of the protease activity and the catalase activity between a certain heavy metal speciation were always to the contrary.