| The number of farms increased with the gradual change of livestock and poultry breeding methods from traditional decentralized mode to intensive and specialized mode,and the production of livestock and poultry manure has also increased.Animal feed additives contain various heavy metals that can promote the growth and metabolism of livestock and poultry,while heavy metals that are not absorbed and utilized enter the environment with livestock and poultry manure.These heavy metals need to be treated harmlessly and as resources.Composting is one of the main methods to treat agricultural wastes such as livestock manure.Although composting can effectively kill bacteria and insect eggs carried in livestock and poultry manure and promote the rapid degradation of organic matter,it cannot effectively solve the heavy metal pollution in the pile.Even after composting,the heavy metals in the heap are relatively concentrated,which increases the risk of environmental pollution.In practical applications,compost is used together with passivators to reduce the bioavailability of heavy metals.Therefore,this study is divided into two parts:(1)Ethyl sulfur nitrogen,biochar,kieselguhr,fly ash,calcium-magnesium-phosphate fertilizer are five passivators.Through different addition time and different addition ratio,explore the physical and chemical properties of passivator compost and the passivation effect of copper and zinc.Five kinds of passivators,namely ethyl sulfide nitrogen,biochar,kieselguhr,fly ash and calcium-magnesium-phosphate fertilizer,were used to study the physical and chemical properties of passivator compost and the passivation effect of copper and zinc.By comparing the differences of heavy metal bioavailability of different passivators,the types,optimal addition ratio and addition period of passivators were determined.(2)According to the test results of the previous part,the physical passivator and chemical passivator are used in combination,and the influence of the composite passivator on the form transformation of heavy metals Cu and Zn is studied,and the appropriate ratio of the composite passivator and the period of addition were determined.The purpose of this study is to provide a reference for the use of compound passivators for composting chicken manure in the future.The results of the study are as follows:(1)The highest temperature of the heap in each treatment group of ethyl sulfide nitrogen exceeded 60℃ for more than 3 days;and it shows a trend of rising sharply in the initial stage and then falling slowly.During the composting process,the pH value first increased,then decreased slightly,and finally stabilized.At the end of the composting process,the pH value was basically stable between 8.0-9.0.At the end of composting,the C/N ratio of each pile was in the range of 16-17.Different addition times and different addition ratios of ethyl sulfide nitrogen have no significant effect on the composting process of chicken manure,and have no significant effect on the physical and chemical properties of the compost.At the same addition ratio,the passivation effect of heavy metals Cu and Zn by adding ethyl sulfide nitrogen on the21 st day of composting was better than that by adding ethyl sulfide nitrogen at other times.Compared with CK(control compost group without passivator),the ability of passivating heavy metal Cu in 8 treatment groups added with ethyl sulfide nitrogen increased by3.03%-24.17%.Compared with CK,the passivation ability of heavy metal Zn increased by2.36%-15.21%.Adding 0.20%(the amount of dry matter in the heap)of ethyl sulfide nitrogen on the 21 st day of composting is more beneficial to improve the passivation effect of chicken manure compost on heavy metals Cu and Zn.(2)At the end of composting,the compost with calcium-magnesium-phosphate fertilizer has higher temperature,higher pH and lower C/N than CK.At the same addition ratio,the passivation effect of adding calcium-magnesium-phosphate fertilizer on the 12 th day of composting is better than that of adding calcium-magnesium-phosphate fertilizer at other times.Compared with the CK group,the 8 treatment groups added calcium-magnesium-phosphate fertilizer had an increase in passivation ability of heavy metal Cu by 8.32%-16.27%,and an increase in passivation capacity of heavy metal Zn by1.84%-5.83%.Adding 7.5% calcium-magnesium-phosphate fertilizer(the amount of dry matter in the heap)on the 12 th day of composting is more beneficial to improve the passivation effect of chicken manure compost on heavy metals Cu and Zn.(3)There was no significant difference in temperature change between the fly ash treatment group and the CK treatment group.At the end of composting,the pH of the fly ash compost is higher than CK,and the C/N is stable at about 16.At the same addition ratio,the passivation effect of adding fly ash on the 12 th day of composting is better than that of adding fly ash at other times.However,compared with CK,the passivation effect of fly ash on exchangeable heavy metal Zn has no significant difference,so it is not suitable for preparing composite passivator.(4)Adding biochar was beneficial to raise composting temperature and increased the duration of composting high temperature period.During the composting process,the pH value first increased,then decreased,and finally stabilized.After the composting process,the pH value of each treatment stabilized between 8.0-9.0.Adding biochar to compost can improve the overall C/N of compost.When adding the same proportion of biochar,the passivation effect of biochar treatment group on the 0th day of composting was better than that of biochar treatment group at other times.Compared with the CK group,the passivation ability of the 8treatment groups with biochar increased by 14.10%-24.42%,the passivation ability of the heavy metal Zn increased by 1.16%-10.23%.Adding 10% biochar(the amount of dry matter in the heap)on the 0th day of composting is more beneficial to improve the passivation effect of chicken manure compost on heavy metals Cu and Zn.(5)Composting temperature of kieselguhr treatment group was higher than CK treatment group.At the end of composting with kieselguhr,the pH value decreased slightly,and stabilized at about 7-8.At the same addition ratio,the passivation effect of kieselguhr treatment group on the 0th day of composting was better than that of kieselguhr treatment group at other times.Compared with the CK group,the 8 treatment groups added kieselguhr had an increase in passivation ability of heavy metal Cu by 9.30%-22.04%,and an increase in passivation capacity of heavy metal Zn by 0.44%-5.36%.Adding 10% kieselguhr(the amount of dry matter in the heap)on the 0th day of composting is more beneficial to improve the passivation effect of chicken manure compost on heavy metals Cu and Zn.(6)Adding 10% biochar,7.5% calcium-magnesium-phosphate fertilizer and 0.2% ethyl sulfide nitrogen as composite passivators on the 0th,12 th and 21 st day of composting can improve the temperature and C/N ratio during composting,and the passivation effect on heavy metals Cu and Zn in chicken manure compost is significantly better than other treatments,which can effectively reduce the activity of heavy metals Cu and Zn in chicken manure compost. |
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