Preparation and Characterization of Micro-nanoscale MSWI Ash and the Effects of Their Metal Release on MSW Anaerobic Digestion

• Main Authors: Hsiao-Hsein Hsu, 徐孝先
• Other Authors: Huang-Mu Lo
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/38181463068967157032

碩士 === 朝陽科技大學 === 環境工程與管理系碩士班 === 96 === This study investigates the preparation of micro-nano scale municipal solid waste (MSW) incinerator (MSWI) ashes and characterizes their metal content and metal compounds. In addition, MSWI ashes and micro-nano scale MSWI ashes are used to co-digest them with MSW in anaerobic bioreactors for comparison. Micro-nano scale MSWI ashes are ground with ball mill (PM 100) by physical grinding. Metal element, particle sizes and microstructure of MSWI ashes including micro-nano scale are measured by field emission scan electrical microscopy (FE-SEM) and X ray energy dispersive spectrometry (EDS). Metal compounds are analyzed by X ray powder diffractometry (XRPD). In addition, MSWI ashes including micro-nano scale are co-digested with MSW to observe the potential enhancement or inhibition of MSW biodegradation. Mixtures of 350 mL refuse substrate and 100 mL sludge seeding are added into the 500 mL anaerobic bioreactors. MSWI fly ash (including micro-nano scale) added ratios onto MSW are selected to be 0.12, 3, 6, 18 and 30 g g-1 VS respectively. Similarly, MSWI bottom ash (including micro-nano scale) added ratios onto MSW are selected to be 0.6, 12, 36, 60 and 120 g g-1 VS respectively. All anaerobic bioreactors are in duplicate and total bioreactors are 42 including 2 control ones. Gas production from bioreactors is recorded daily. Daily measurements also contain pH, ORP, EC, Salinity. Weekly analyses include COD, TS, TVS and metals. These measured parameters are used to evaluate the performance of anaerobic bioreactors with different ratios of MSWI ashes addition. At final stage of anaerobic digestion, solid digestate is taken out for parameters analyses such as C, N, H, P, K, pH, C/N, K2O, P2O5, TCLP and metals. These measured parameters will be used to assess the utilization possibility as organic fertilizer and as soil amendment in agricultural and forest. Results show that intensity of SiO2, CaCO3, PbO and ZnS increased after grinding. However, intensity of Al2O3 and CaMg(CO3)2 were found to decrease. Particle sizes less than 100 nm were found to increase. With regard to co-digestion of MSWI ashes and MSW, gas production of MSWI bottom ash/MSW ratios (BA/MSW ratios) of 12, 36 and 60 g g-1 VS (2177.5, 2492.5, 1970 mL) and MSWI fly ash/MSW ratios (FA/MSW ratios) of 6, 18 and 30 g g-1 VS (1917.5, 1985, 2047.5mL) were found to be higher than control one (852.5 mL). Gas production of similar ratios of MSWI micro-nano scale bottom ash/MSW (NBA/MSW ratios) and similar ratios of MSWI micro-nano scale fly ash/MSW (NFA/MSW ratios) were found have higher gas production than that in the BA and FA added bioreactors. NBA/MSW ratios of 12, 36 and 60 g g-1 VS and NFA/MSW ratios of 6, 18 and 30 g g-1 VS were found to have gas production of 2300, 2705 and 2465 mL and 2132.5, 2070 and 2170 mL respectively. Heavy metals released from the added ashes in the anaerobic bioreactors were found to have the order of Zn (0.0061-4.8661 mg l-1) > Cr (0.0048-2.8715 mg l-1) > Cu (0.0047-0.8867 mg l-1) > Ni (0.0057-0.2211 mg l-1) > Cd (0.0085-0.142 mg l-1) > Pb (0.0049-0.1368 mg l-1). Released levels of heavy metals from ground MSWI ashes were found to be higher than those of unground ones. It indicates that ground MSWI ashes have smaller particles than unground ones resulting in the higher adsorption of heavy metals on MSW. It is also thought that suitable levels of trace metals nutrients may be released from ground ashes resulting to a higher gas production than that of unground ones. For resource purpose, solid digestate of co-digestion mixture were measured to have suitable pH and C/N ratios indicating its suitability for organic fertilizer or soil amendment. It is therefore concluded that micro-nano scale MSWI ashes can be achieved by physical grinding. Suitable ratios of micro-nano scale ashes to MSW could enhance higher gas production than that of unground ashes. These results can be for reference to co-digestion or co-disposal of MSW and MSWI ashes.