The Study On Soil And Water Environment Impact Of Open-air Vermicomposting Under Simulating Rainfall

Vermicomposting is a kind of low-carbon and environmental-friendly technology on livestock and poultry manure.At present,most of the vermicomposting processes are carried out in an open air environment.However,its effect on the environment is unclear.Therefore,a study with pig manure,cow dung,sludge and earthworm "Daping 2" as composting materials was set under the simulated rainfall conditions to investigate the effect of different compost methods on the main elements in surface runoff water and soils,which could provide a theoretical basis for assessing the impact of open-air composting on the soil and water environment.The simulated rainfall was set as big(7mm),middle(20mm)and small(40mm),respectively,according to the annual rainfall and distribution characteristics in Sichuan Statistical Yearbook.And there were 9 groups including pig manure,pig manure and earthworm,vermicompost on pig manure,cow manure,cow manure and earthworm,vermicompost on cow manure,sludge,sludge and earthworm and vermicompost on sludge in the experiment.The test period is 4 weeks.Rainfall occurs every Tuesday,Thursday and Saturday.The surface runoff water samples were collected after each rainfall,and the composting substrates and soils were sampled after the 4 weeks rainfall was completed to analyze the total nitrogen,total phosphorus,total copper and total zinc in surface runoff,substrate and soil samples.The main results are as following:1.During the rainfall,the N and P contents of surface runoff water increased with the increasing of rainfall,but the content of Cu and Zn decreased with its increasing.And the amount of elements in surface runoff water is positively correlated with the original content of substrates under the same rainfall condition.2.The highest content of N,P,Cu and Zn in surface runoff water was get at the first rainfall,and then decreased gradually.Specifically,the highest N content(52.5mg/L)in surface runoff water was detected after the first and second rainfalls,which exceeded standard seriously(the second-class standard of GB8978-1996 is 25mg/L).And the highest value was 7.56mg/L that is lower than the GB first-class standard(15mg/L).The P content in surface runoff collected from the first to the sixth rainfall was up to 26.29mg/L,far exceeding the second-class standard of GB8978-1996(1mg/L),and its content only reached 0.49mg/L,in line with a discharge standard(0.5mg/L)after the seventh rainfall.The highest concentration of Cu collected in surface runoff water is 0.02 mg/L and Zn content is 0.11 mg/L.All of them meet the GB8978-1996 first-class standards(0.5 mg/L and 2 mg/L).The contents of Cu and Zn produced by single rainfall will not affect the water environment.3.The variation of each element in the base material with the times of rainfalls is: the amount of loss was high in the early stage,and it decreased gradually until approaches to zero.The loss of N and P in surface runoff is mainly concentrated in the first 6 times;the loss of Cu on the surface flow is mainly concentrated in the first 2 times,and the loss of Zn on the surface runoff is mainly concentrated in the first 4 times.4.In this experiment,important elements in the substrates can flow into the soil with the infiltration of rainwater.However,the N,P content increased slightly only in part of the soil?which improved the soil fertility,and nosoil pollution of heavy metals was founded.