The Study On Migration Of Heavy Metals In The Process Of Thermo-chemical Treatment Of Municipal Sewage Sludge

The increased quantity of municipal sewage sludge is becoming a rigorous challenge to our country's economic development and people's living environment, which reminds us of the urgent need for reasonable treatment method of sludge treatment and effective disposal technology of heavy metals in sewage sludge. Pyrolysis, gasification and incineration are the common resource utilizations of sewage sludge. Thermal hydrolysis is a simple, efficient,low consumption technology of sewage sludge treatment. On the one hand, carbonation treatment can be able to absorb and fix a part of CO2, and on the other hand carbonation can improve the stability of heavy metals, which is of great significance in researching the effects of thermochemical treatment on the migration law of heavy metals in sewage sludge.In this paper, firstly, series of thermal hydrolysis were used to treat three kinds of municipal sewage sludge to determine the effects of temperature and processing time on the migration law of heavy metals containing Hg, Cu, Zn, Cd, Cr, Co, Ni, Pb. The leachability of heavy metals were analyzed after thermal hydrolysis by the application of horizontal vibration method. Results showed that increasing thermal hydrolysis temperature was favorable to dissolve Hg into the liquid phase, but was not conducive to the dissolution of other heavy metals. Increasing processing time had a positive effect on dissolving heavy metals into liquid phase. Thermal hydrolysis could significantly reduce leaching toxicity of heavy metals, and the leachability of heavy metals would further reduce as temperature or processing time rises.Secondly, alkaline thermal hydrolysis was used to treat sludge to research the effects of temperature and processing time on the migration law of heavy metals, and analyze the changes of heavy metals' leaching toxicity. Results showed that after alkaline thermal hydrolysis, the content of heavy metals in solid phase was increased, and alkaline thermal hydrolysis promoted the stability of heavy metals. Increasing temperature was favorable to transfer Hg to the liquid phase, but went against the dissolution of other heavy metals.However the leaching toxicity of most heavy metals decreased. Increasing processing time had a positive effect on dissolving most heavy metals into liquid phase, and the leaching toxicity of heavy metals did not change significantly.Finally, pyrolysis, gasification and incineration were used to treat three kinds of municipal sewage sludge by using horizontal tube furnace, in order to analyze the release law of heavy metals in different atmosphere. The effect of carbonation on heavy metals and fixing CO2 was studied by treating sludge incineration ash. Results showed that after pyrolysis, gasification and incineration, solid residue and gas products both contained a large variety of heavy metals, and increasing temperature had a positive effect on the release of heavy metals. The leaching toxicity of heavy metals could be reduced by carbonation treatment of sludge incineration ash, and the change of temperature had little effect on the leaching toxicity of heavy metals. With the rising of carbonation temperature, the effect of carbon fixation firstly increased and then decreased.