| Sewage sludge has high water content,and contains a lot of bacteria,pathogens and heavy metals,so reduction,detoxification,stabilization and recycling become the principle and goal of its treatment and disposal.As a new biomass energy conversion technology,hydrothermal carbonization has great advantages in sludge reduction and detoxification treatment.Based on this,this paper studies the feasibility of hydrothermal carbonization as a treatment technology of sludge stabilization and resource utilization,and proposes the method of sludge mixed with banana stalk to improve the quality of the hydrochar derived from sludge.It is of great significance for hydrothermal carbonation to become a feasible and excellent sludge treatment technology and to solve the sludge disposal dilemma in China.Firstly,the changes of physical and chemical properties and combustion behavior of sludge before and after hydrothermal treatment(temperature variable is 180℃,230℃,280℃).Through element analysis and proximate analysis,it can be concluded that the content of N and S in hydrochar of sludge is greatly reduced,which is beneficial to its clean utilization.Meanwhile,the atomic ratio of H/C and O/C decreased,which indicated the improvement of coalification degree.However,with the increase of temperature,the ash content of hydrochar increased significantly,and the calorific value decreased.Therefore,there are some defects of sludge hydrothermal carbonization,such as low utilization rate and poor combustion performance.Secondly,based on the previous experiments,the total amount and distribution of heavy metals in hydrochar were determined by CJ/T 221-2005 and GB/T 25282-2010 respectively.The results showed that most of Cd,Cr,Cu,Pb and Zn are retained in hydrochar except a small amount of As and Ni which can be dissolved,which resulted in the enrichment effect of heavy metals.However,hydrothermal carbonization is conducive to the transformation of the unstable form of heavy metals to relatively stable and stable form,effectively reducing the risk index and risk level of heavy metals in the sludge.Finally,the experiment of banana stalk co-hydrothermal carbonization was carried out under different sludge mixing ratio(30%,50%,70%).It is found that the co-hydrothermal carbonization has synergistic effects on the yield,calorific value and energy recovery.The properties of the co-hydrothermal carbonization were affected by the carbonization and synergistic effect.When the mixing ratio of sludge was 30%,hydrochar achieved the best coalification degree and calorific value at 280 ℃,and the lowest burnout temperature and the best combustion performance at 180 ℃.Therefore,co-hydrothermal carbonization had a good performance in remedying the performance defects of sludge hydrochar.In addition,it had no obvious effect on the stabilization of heavy metals.In general,the co-hydrothermal carbonization of sewage sludge and banana stalk is an effective way to realize the stabilization and resource utilization of sewage sludge. |
