Preparation And Resource Utilization Of Sewage Sludge-based Biochar

Large numbers of sludge are produced in sewage treatment plants.Sludge(80%moisture content)are expected to increase to 60 million tons in 2020.Therefore,how to treat sludge safely and efficiently and recycle it have become a research hotspot.At present,traditional disposal methods of sludge include landfill,agricultural application,incineration and pyrolysis.Landfill has become unacceptable due to the rapid depletion of available space and high environmental costs.As for the application of sludge in agriculture,it may cause many problems such as the accumulation of heavy metals in soil,plants and animals.The preparation of sludge into biochar,as an effective treatment method,can realize the sludge harmless,reduction and reuse at last.However,the sludge is prepared separately into biochar.Due to its high dissolution rate of nutrients and poor adsorption performance,it is usually necessary to modify it.From the perspective of improving the adsorption performance of sewage sludge-based biochar,sludge was used as raw material in this paper and modified by adding a series of crop straws and ore materials and sludge carbonization.Sewage sludge-based biochar was prepared by high temperature pyrolysis and hydrothermal carbonization.The effects of its retention of nutrient elements and adsorption of heavy metals were studied.The main conclusions are as follows:(1)The aromatization of sewage sludge-based biochar was deepened by adding modified substances,and the hydrothermal sewage sludge-based biochar had more oxygen-containing functional groups.The content of heavy metals in sewage sludge-based biochar can be reduced by adding modified materials.In addition,the co-pyrolysis of sludge and modified materials can improve the thermal stability of sewage sludge-based biochar.(2)Adding modified materials can improve the adsorption capacity of some sewage sludge-based biochar to nutrient elements in water.Application of sewage sludge-based biochar to soil can reduce the leaching loss of nitrate,ammonium and phosphate.And adding modified substances can further improve the slow-release effect of sewage sludge-based biochar on nutrient elements in soil.Compared with the original sewage sludge-based biochar,the sewage sludge-based biochar with 5%graphite powder reduced the nitrate leaching amount by 51.17%.Therefore,the addition of modified materials is helpful to improve the ability of sewage sludge-based biochar to retain nutrient elements.(3)Adding modified materials can improve the adsorption capacity of sewage sludge-based biochar to heavy metals.Compared with the unmodified sewage sludge-base biochar(HC),adding the modified materials can improve the sewage sludge-based biochar(HC-M、HC-K、HC-I)adsorption of Pb(Ⅱ),which increasing was 45.73%,43.21% and 42.18%,respectively.By comparing the sewagesludge-based biochar prepared by the two methods,it is found that the adsorption of heavy metals by hydrothermal sewage sludge-based biochar takes longer time to reach the equilibrium state.And hydrothermal sewage sludge-based biochar for the same molar concentration of Cd(Ⅱ)and Pb(Ⅱ)adsorption capacity increased,increased by 86.39% and 10.57%,respectively,but for the same molar concentration of Cr(Ⅵ)adsorption quantity is decreased by 24.57%.