| Summary: | 碩士 === 逢甲大學 === 環境工程與科學所 === 95 === This study investigated the mobility of heavy metals and nitrogen on immature or mature sewage sludge compost for land application. The experiments were conducted by simulated soil column with constant rainfall and relationship between the metal or nitrogen mobility and organic matter was also evaluated. The experimental results indicated that the functional group of Aliphatic and Polysacharides were transformed into the functional group of Aromatic and Alkene in sewage sludge composting. In case of the immature or mature compost for land application, the functional group of organic matter in compost and soil were changed insignificantly. However, the functional group of Aromatic in leachate from soil was measured. It would understand the organic matter transformation and facilitate the plant uptake.
Based on the results of the leachability of heavy metals in sludge, immature or mature sludge compost for land application, in case of the sewage sludge application, the leachabilities of metals were in decreasing order as Ni>Zn>Cu>Pb (low metal concentration test ) and Ni>Zn>Pb>Cu (high metal concentration test), respectively. In case of the immature compost application, the leachabilities of metals were in decreasing order as Ni>Zn>Cu>Pb (low metal concentration test) and Ni>Zn>Pb>Cu (high metal concentration test), respectively. Meanwhile, in case of the mature compost application, the leachabilities of metals were in decreasing order as Zn>Ni>Cu>Pb (low metal concentration test) and Zn>Pb>Cu>Ni (high metal concentration test), respectively. According to the results of land application of sludge or compost with low metal concentration, Zn, Cu and Ni were accumulated and detected at soil depth of 10-30 cm. However, Pb was remained at compost or soil depth of 2-5 cm.
In this study, the retardation factor of the metals in the soil was a critical factor for assessing the metals mobility. Accordingly, the results of retardation factor of the metals were Ni>Zn>Cu>Pb (sludge test), Ni>Cu>Pb>Zn (immature compost test), and Ni>Pb>Cu>Zn (mature compost test), respectively. These results would concluded that the mature compost had higher metal retardation ability. That is, the metals mobility was low relatively in mature compost land application. On the other hand, in case of the immature or mature compost application, Zn concentration of leachate was higher than other tested metals of that. Meanwhile, Zn is a metal with low retardation ability. Therefore, it could conclude that the Zn is a metal with higher mobility. The total nitrogen contents in soil and leachate were high during the land application of mature compost. This is due to the mature compost has higher availability of total nitrogen.
According to the results of relationship among the physicochemical characteristics of leachate, maturity of compost and heavy metals concentration of leachate, the relationship between the pH and Zn, Pb concentration was shown in positive corelationship insignificantly (p<0.01, r=0.299 (Zn); p<0.01, r=0.319 (Pb)). The relationship between the EC and Cu concentration was also shown in positive corelationship insignificantly (p<0.01, r=0.257). However, the relationship between the EC and Pb, Ni concentration was shown in positive corelationship significantly (p<0.01,r=0.413(Pb)；p<0.01,r=0.560(Ni)). In this study, the results also indicated that the relationship between the maturity of compost and heavy metals concentration of leachate was significant. The heavy metals concentrations of leachate were high while the immature compost was applied as the fertilizer for the agricultural application.
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