污泥生物炭制备过程中氮磷钾及重金属的迁移行为

Transformation of nitrogen,phosphorus,potassium and heavy metals during sewage sludge biochar preparation

采用固定床反应器对脱水污泥在热解过程中N、P、K及重金属的迁移行为进行了研究,以期获得营养元素N、P、K含量较高、重金属含量较低的生物炭,将其作为土壤肥料。结果表明,污泥样品中N主要以铵盐-N、蛋白质-N、吡咯-N、吡啶-N 4种形态存在,其中吡咯-N占总氮的45.22%,热解后各组分在生物炭中所占比例发生变化,其中吡咯-N的减少较为明显,800℃的污泥炭中减少到3.24%。随着热解温度由400℃升高到800℃,N在污泥炭中的含量逐渐降低,气相中的含量明显增加,但液相中在600℃后减少;P和K几乎全部集中在污泥炭中,其中400℃污泥炭中的P主要以焦磷酸盐形式存在、800℃时则主要以偏磷酸盐存在;重金属在污泥炭中出现不同的富集,其富集程度顺序为:Cu>Ni、As>Pb、Cr>Zn>Cd。

The transfer behaviors of nitrogen,phosphorus,potassium,and heavy metals during sewage sludge pyrolysis in a fixed-bed reactor were investigated. The purpose of this study was to obtain sludge biochar,which is rich in nutrients such as N,P,and K and contains less heavy metals,as soil fertilizer. Results indicated that the nitrogen existed in raw sludge in the forms of ammonium salt-N,protein-N,pyrrole-N,and pyridineN; pyrrole-N amounted to 45. 22% of total nitrogen. After pyrolysis,the proportion of nitrogen components in biochar changed,and the pyrrole-N content decreased obviously to 3. 24% at 800 ℃. When pyrolysis temperature increased from 400 ℃ to 800 ℃,the total nitrogen content in biochar decreased. It increased gradually in pyrolysis gas,but decreased in the liquid above 600 ℃. Almost all P and K remained in the sludge biochar. The phosphorus in biochar at 400 ℃ existed mainly in the form of pyrophosphate,and mainly as metaphosphate in biochar at 800 ℃. There were differences in the content of heavy metal species. The order of heavy metal content in the biochar was as follows： Cu〉 Ni,As 〉Pb,Cr〉 Zn〉 Cd.