| Utilization of resources is the main way to solve the problem of sludge disposal and development direction,and sludge land use is always limited by heavy metal pollution in sludge.So the heavy metal pollution in sludge is one of the problems that need to be solved urgently when it is used in agriculture.How to reduce the environmental risk of sludge has been paid more and more attention by researchers.Through the application of sludge aerobic fermentation technology in sludge treatment and disposal project,the dynamic transformation regularity of heavy metals,the fertilizer efficiency of aerobic fermented sludge and the safety of soil utilization are comprehensively evaluated in this paper,which provides technical basis for the practical engineering of municipal sludge safe disposal and resource utilization.Taking the sludge treatment and disposal project of a sewage treatment plant in Tianjin as an example,the dynamic transformation regularity of heavy metals in the sewage treatment-sludge aerobic fermentation process of the project was analyzed and studied.Samples were taken at different time intervals,and the results showed that the content of heavy metals in sewage changed regularly in different stages of the process,although heavy metals in the sewage was enriched,but the heavy metal content in aerobic composting sludge was similar to that in garden soil,and the soil fertilizer efficiency index increased linearly with the increase of fertilization ratio.By analyzing the variation of nutrient elements and heavy metal contaminants in sludge before and after aerobic fermentation,different proportions of aerobic fermented sludge were mixed with garden soil,and the variation of available nitrogen,phosphorus and potassium in plant after mixing was analyzed.Record the influence on germination rate of balsamine,peacock grass,ryegrass and tall fescue which manuring with different ratio of fermentation sludge,also evaluate its efficiency on different types of crop production.As a result,two green plants had better tolerance to composting sludge than other two flower plants.All the four plants can grow in different fertilization proportion of soil,except peacock grass,the other three plants grow best in 100% compost sludge,indicating that the compost sludge can be directly used to cultivate landscaping plants.Balsamine,peacock grass,ryegrass and tall fescue grew best at 5-10% fermented sludge.Compared with plants growing in garden soil,aboveground biomass increased 1-7 times,especially ryegrass.The application of fermented sludge in the range of 5-10% could effectively increase the root-shoot ratio of Balsamine,but had no significant effect on the other plants.After the seedling stage,the plants can grow directly in 100% of the fermented sludge and grow vigorously.The sludge quality after aerobic fermentation was analyzed.The water content and volatile organic matter of the treated sludge decreased rapidly.The effect of biological drying(dehydration)and stabilization was very obvious.In order to ensure the quality of the fermented sludge,it was necessary to strictly control the discharge of industrial wastewater,combined with element toxicity and its content in sewage and sludge samples and the enrichment in the underground part of the plant,it should be pay more attention to heavy metals such as Ni,Zn,Cr,Cu and Mn.By applying aerobic fermentation sludge,the content of heavy metals in plant rhizosphere soil will increase slightly.If heavy metals exceed the standard,leaching and other pretreatment methods should be adopted to ensure the safety of fermented sludge.Especially when considering as forage fertilizer,more attention should be paid to avoid polluting greening soil and animal feed. |
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