| The output of sludge is increasing year by year.As a high resource treatment and disposal method of municipal surplus sludge,carbonization technology has been highly valued in China in recent years.In recent years,the constructed wetland has been well developed in the process of urbanization in China.The dead wetland plants with large reserves and high value of resource utilization also have good prospects in the field of carbonization.In this paper,the sludge and a variety of typical wetland plants were mixed for carbonization,and the effect of mixed carbonization was studied by single factor experiment and solid characterization.The practical effect of the sludge on soil improvement was determined by the preliminary experiment of fertilizer conservation.The purpose of this paper is to solve the problems of low utilization rate of sludge and wetland plant resources,and unsatisfactory properties of sludge biochar alone.At the same time,it provides a new idea for carbonization process.The main conclusions of this paper are as follows(1)The carbon contents of reed,renewables and cattail were 47.8%,45.94%and 46.21%respectively,which were higher than 35.0%of sludge.The volatile content of sludge was 30.5%which was far lower than 90.8%,91.57%and 94.4%of reed,renewables and cattail.The ash content of sludge was 40.3%which was higher than 3.2%,2.6%and 3.9%of reed,renewables and cattail.Wetland plants contain higher volatile matter,lower ash and higher carbon content,indicating that wetland plants contain higher organic matter content(2)The best carbonization conditions for the preparation of sludge biochar are carbonization temperature of 500℃,holding time of 30 minutes,particle size of sludge raw material of 70 mesh,under which the iodine adsorption value of sludge biochar is 183.6 mg/g,and the yield is 57.7%.The results show that the specific surface area is 23.6 mg/g and the average pore size is 10.71 nm,and the functional groups mainly contain hydroxyl,carboxyl,side chain group,benzene ring and so on(3)The best carbonization conditions for three kinds of wetland plants to prepare wetland plant biochar are:carbonization temperature 350℃,holding time 30 min,raw material particle size 70 mesh.Under this condition,the iodine adsorption values of reed,renewables and cattail biochar are 261.4 mg/g,280.4 mg/g and 295.5 mg/g respectively,and the biochar yields are 40.0%,35.9%and 40.8%respectively.The characterization results showed that the specific surface areas of biochar of three wetland plants were 83.61 m2/g,92.35 m2/g and 105.87 m2/g respectively,and the functional groups mainly contained hydroxyl,carboxyl,side chain groups and a small number of benzene ring functional groups(4)The best carbonization conditions for the preparation of mixed biochar are carbonization temperature 400 ℃,holding time 60 min,raw material particle size 70 mesh.Under the conditions,the iodine adsorption values of the mixed carbonization products of sludge,reed,renewables and cattail are 232.8 mg/g,243.4 mg/g and 245.8 mg/g respectively.The results showed that the specific surface areas of the mixed biochar were 58.2 m2/g,68.96 m2/g and 71.82 m2/g respectively.It can be seen that the mixed carbonization of wetland plants and sludge can effectively improve the adsorption performance of sludge biochar.SEM shows that there are more pores on the surface of mixed biochar than that of sludge biochar,and the wall of the pores is thinner.The surface of cattail sludge mixed biochar is honeycombed,and obvious pores can be seen at 5000 times,and the surface is attached with small particles blocking the pores.FTIR results showed that the mixed biochar was rich in functional groups.(5)The leaching rate of nitrogen and phosphorus decreased with the increase of biochar dosage.When the dosage of biochar increased from 0 g to 10 g,the leaching rate of nitrogen and phosphorus decreased from 51.4%and 11.8%to 32.1%and 3.4%at the beginning of 24 h,respectively.The leaching rate of accumulated nitrogen and phosphorus decreased from 61.3%and 27.3%to 42.3%and 6.1%respectively.The addition of biochar can retain nitrogen and phosphorus in soil column.Slow release fertilizer has a certain slow release effect on nitrogen and phosphorus in soil Compared with soil fertilizer and soil slow-release fertilizer,the leaching rate of nitrogen and phosphorus in the early 24 h of soil slow-release fertilizer was 18.3%and 1.2%,which was lower than 32.2%and 3.1%of that in the early 24 h of soil fertilizer The leaching rate of accumulated nitrogen and phosphorus in 10 days was 33.4%and 3.2%in SRF group,which was lower than 62.2%and 6.5%in SRF group.The retention effect of biochar based slow-release fertilizer is more obvious than that of biochar. |
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