高温热解对污泥炭特性及其重金属形态变化的影响

EFFECT OF HIGH TEMPERATURE PYROLYSIS OF SEWAGE SLUDGE ON CHARACTERISTICS OF RESIDUAL BIOCHAR AND SPECIATION CHANGES OF HEAVY METALS

温度是影响污泥热解产物性质的主要因素之一。研究了热解温度(550,700,850℃)对污泥炭性质、结构和重金属含量及其形态变化的影响。结果表明:污泥炭产率(55. 83%)和H/C(0. 05)在热解温度为850℃时达到最小值。而当热解温度为700℃时,其pH值、比表面积及污泥炭中各重金属总量与残渣态百分比(F4)均为最大值,同时其所含各重金属中生物有效态(F1+F2)的质量分数也均为最低值,即污泥中各重金属潜在的生态风险水平处于最低水平。而当温度升至850℃时,污泥中各重金属相对稳定态质量分数(F3+F4)有所减小,这可能是由于高温条件下金属易随热解气挥发所导致。故700℃是提升污泥炭质量和钝化污泥中重金属、降低其生态风险的最佳温度。

Temperature is one of the key factors which govern the characteristics of the pyrolysis product of sewage sludge. This paper investigated the effect of different pyrolysis temperatures( 550,700 and 850 ℃) on the property,ultrastructure of sludge biochar as well as heavy metal contents and speciation changes inside. The results showed that sludge carbon yield( 55. 83%) and H/C( 0. 05) reached the minimum value at 850 ℃. When the pyrolysis temperature was 700 ℃,the pH value,specific surface area,the total amount of heavy metals in sludge carbon and the percentage of residual state( F4) were all the maximum. At the same time,the bioavailable concentration( F1+F2) of heavy metals dropped to the minimum. In other words,the ecological risk of the heavy metals contained in the sludge was minimized. However,when the temperature was raised to 850 ℃,the percentage of stable heavy metal speciation( F3+F4) declined to some extent,which might be caused by volatilization of metals with pyrolysis gas at high temperature. The outcomes of this study implies that 700 ℃ was the optimal temperature for improving sludge biochar,immobilizing the heavy metals in sludge and minimizing their ecological risk.