| Small municipal sewage treatment plants produce less amount of sludge with better mud quality.The cost of transportation to the outside of the plant after drying treatment is higher,and it does not meet the requirements of economic convenience.Stabilization and greenbelt application are effective ways to achieve resource recycling.At present,aerobic composting is the best sludge treatment and disposal method.Biochar is commonly used as an additive for composting.Different amounts of biochar added to the pile will affect the p H,moisture content,nitrogen,phosphorus,etc.of the pile.And they make the compost effect significantly different.Therefore,it is necessary to study the amount of biochar added with the best compost effect,but little research has been done on the amount of biochar added and its effect on the greenbelt application of sludge after composting.At the same time,when composting sludge is used for land use,the effects of heavy metals in the sludge on plants and groundwater must be considered.Therefore,a time-temperature control system was used for sludge aerobic composting in our study,and different amounts of biochar were added as additives to explore the optimum amount of biochar.And research were also made on the feasibility of composting sludge for gardening after composting.Research results are as follows:1.In the process of sludge composting,the volume ratio of sludge: corn cob:biochar is 10:6:2 can maintain the high stage of temperature for a longer period.The p H and water content also satisfy the decomposed requirements of sludge aerobic composting.The result also showed that composting with biochar addition has better nitrogen retention than that without biochar.2.For the five heavy metals(Cu,Zn,Pb,Ni,Cr)in the sludge,the aerobic composting process has a good passivation effect on transformation of Cr,and the residual Cr content is obviously increased.The content of residual Cu and Pb content is over 50%.And the residual ratio of Ni and Zn is about 40%,and the exchangeable content is not significantly decreased,and the passivation effect is not obvious.3.The bacterial diversity in the process of composting with different amounts of biochar added was measured and analyzed.The results showed that the addition of biochar had a significant effect on the bacterial species in the compost.There are obvious differences in the types of bacteria in the treatment between composting without biochar and composting with other four biochars.When the volume ratio of sludge: corn cob: biochar is 10:6:2,the life activity of bacteria is the most active,and the functional gene representing bacterial activity is high.4.The composted sludge is mixed with the garden soil,and it is found that the longitudinal migration of heavy metals in the mixed soil don’t cause harm to the groundwater.The mixed soil obtained by mixing compost sludge and garden soil was used for tall fescue planting.It was found that heavy metals in the sludge had certain inhibition on the germination and growth of tall fescue.At the same time,the abundant nitrogen and phosphorus in the sludge will also promote the growth of tall fescue.When the compost sludge that the volume ratio of sludge: corn cob: biochar is 10:6:2 is mixed with garden soil at a ratio of 40% for tall fescue planting,the germination and growth of tall fescue is the best. |
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