| Summary: | 碩士 === 逢甲大學 === 環境工程與科學所 === 91 === Abstract
This study focused on the uptake and variation of heavy metals in a sewage sludge composting process using natural zeolite as an additive. Meanwhile, the correlation between the organic matter transformation and heavy metal in a sewage sludge composting, using the E4/E6 ration of fulvic acid and humic acid , FTIR and 13C-NMR technigues, was also discussed. Based on the physicochemical characteristics of the co-compost, the potential use for the sewage sludge compost as soil conditioner or manure is suggested, all complying with the criteria of the compost quality. The total concentrations of Zn, Cu, Cd, Ni and Pb in the compost product were far below the limit values for agricultural use. The results of TCLP analysis for the compost were all in compliance with EPA regulatory limits.
For heavy metal distribution analysis, the Iron and Manganese(Fe-Mn) oxides fraction of Zn was the major fraction. Meanwhile, the exchangeable fraction of Zn increased with the composting time. That is, it means that the Zn is an unstable metal in composting. The organic and Fe-Mn frations oxides fraction of Cu were the major fraction, and the exchangeable and carbonate fractions of Cu decreased with the composting time. The percentages of exchangeable, carbonate and Fe-Mn oxides fractions of Pb and Ni decreased significantly in the composting process. Besides, in the case of zeolite addition, the results of organic and residual fractions of Ni were higher than other controlled test. The natural zeolite additive has adsorption and exchange capacity for reducing the mobility of Ni. However, the distribution of Cr was residual fraction in the compost, and the Cr speciation would be more stable in the composting process. Accordingly, the heavy metals may reduce the mobility in the composting process, except Zn, and may enhance the feasibility for agricultural use.
The results of E4/E6 ratio of fulvic acid and humic acid indicated that the E4/E6 ratio increased with organic matters decomposition. However, increasing the composting time may tend to synthesize more larger organic matter. Therefore, the E4/E6 ratio of humic acid was less than 5. The results of FTIR analysis and it’s peak intensity variation showed that biodegradable organic matters, such as aliphatic and
polysaccharide compounds, were decomposed and transformed to more stable organic compounds, such as alkene, aromatic compounds, and aromatic rings. On the other hand, the results of 13C-NMR analysis revealed that the area of aliphatic region decreased gradually. Meanwhile, the area of aromatic, carboxyl and ester regions increased in the composting process. These above results were similar to the results of FTIR analysis. Accordingly, biodegradable organic matters in the sewage sludge will transform to more stable aromatic compounds in the composting.
The correlation between heavy metals and organic matters transformation showed that DTPA-Pb concentration decreased with an increase of Pb total concentration, however, DTPA-Ni concentration increased with an increase of Ni total concentration. The correlation between the DTPA and SCE (sequential chemical extraction) concentrations indicated that the good relationship between DTPA-Zn concentration and exchangeable fraction. That is, the DTPA-Zn concentration was presented as the exchangeable fraction. The DTPA-Cu concentration increased with an increase of Cu organic fraction. The highly positive relationship between the DTPA-Ni concentration and Ni exchangeable and carbonate fraction. In addition, the results of heavy metals and organic matters transformation showed highly positive relationship between the ratio of alkene C/aliphatic C and the total concentration of Cu and Pb. Meanwhile, the aliphatic C content decreased with an increase of alkene C content.
Keywords: Sewage sludge, heavy metal, fulvic acid, humic acid, DTPA, Sequential Chemical Extraction
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