Effects Of Different Pyrolysis Conditions On Carbon Characteristics And Heavy Metal Behavior Of Sludge

To realize the passivation and stabilization of heavy metals in sludge biochar and to minimize the potential ecological risk of sludge biochar utilization is the core problem related to the safe utilization of sludge biochar,and it can promote the engineering application of sludge pyrolysis treatment technology.It is of great significance to realize sludge reduction,stabilization,innocuity and resource treatment.In recent years,pyrolysis is considered as an environment-friendly technology because of its simplicity and cleanliness.However,the behavior and environmental risk of sludge carbon and heavy metals under different pyrolysis conditions need to be further studied and discussed.In this study,the characteristics and heavy metal behavior of sludge carbon under high temperature pyrolysis treatment were studied under three conditions: pyrolysis temperature,residence time and the ratio of rice husk to rice husk.At the same time,the factors influencing the heavy metal transport behavior of sludge carbon were studied,and the RAC risk assessment of heavy metals in sludge carbon was carried out.The results show that:When the pyrolysis temperature is 850 ?,the sludge carbon yield(55.83%)and H/C(0.05)are the minimum,while the pH value and specific surface area are the maximum at 700 ?.At the same time,the concentration percentage of the heavy metals stored in the bioavailability(F1+F2)and the bioavailability of heavy metals were also the lowest,that is to say,the potential ecological risk level of the heavy metals in sludge was the lowest.However,when the temperature rises to 850 ?,the relative stable percentage of heavy metals(F3+F4)in sludge decreases,which may be due to the volatility of metals with pyrolysis gas at high temperature.Caused by.According to the RAC risk evaluation,except Cu and Mn elements,the other four metal elements are either low risk or no risk state.It is suggested that 700 ? is the best temperature to improve the carbon quality of sludge and to reduce the ecological risk of heavy metals in passivated sludge.The retention time of pyrolysis increased gradually(1h),the sludge carbon yield and H/C ratio decreased in varying degrees,while the ash content and specific surface area increased significantly,and the degree of aromatization of sludge carbon also increased significantly.Compared with SS,the risk coefficients of each heavy metal in SSB decreased significantly.When the retention time of pyrolysis was 2 h,the other five metal elements in sludge carbon showed low risk or no risk except Zn.When theresidence time is 2h,it is the best choice to improve sludge carbon quality and reduce the ecological risk of heavy metals.The addition of different proportion of rice husk and sludge in pyrolysis process changed the behavior of heavy metals in sludge.When the ratio of rice husk to rice husk was 50,the sludge carbon yield and H/C and O/C ratios were the minimum,while the pH value and specific surface area reached the maximum,and the degree of aromatization of sludge carbon increased obviously.At the same time,the content of heavy metals in activated sludge carbon caused by rice husk decreased significantly.According to the RAC risk assessment,the risk levels of Cu,Zn,Mn and Ni in sludge carbon decreased in varying degrees when the ratio of rice husk to rice husk was 25%,compared with the original sludge,but when the ratio of adding rice husk was 50%,the risk level of Cu,Zn,Mn and Ni in sludge carbon decreased in varying degrees.With the exception of Cu,all heavy metals in sludge carbon were of low risk or no risk.The results showed that the co-pyrolysis of sludge with rice husk could effectively reduce the potential ecological risk level of heavy metals in sludge and the treatment effect was optimal when the ratio of rice husk to rice husk was 50%.