| Landfilling is an important option for MSW management in both developed and developing countries. As a result, there are hundreds of thousands of landfills in which a huge quantity of MSW is being placed. The wastes in landfills will become stablized and humified as these wastes degrade over time. The resultant degraded waste in landfill is referred to as "aged refuse" in this work. Actually, the aged-refuse could be considered as recyclable resource and its excavation and recycling should be a potential solution for MSW management alternatives, including remediation of dumping sites and sanitary landfills.Humic acids are important chemicals in the nature. The aged refuse contains a proportion of humic acids and its separation and characteriztion can be helpful to the understanding of aged refuse properties and stabilization of wastes in landfills. In this work, the aged refuse with a placement age of 6 to 10 years were sampled from Shanghai Laogang Refuse Landfill located along the shore of East China Sea, a largest landfill in China. The Landfill is divided into 49 landfill compartments, with around 60,000 m~2 each compartment and a refuse height of 4 m. Hence, the Landfill is suitable for the study on the characterization of aged refuse, both for sampling and quantification.Original aged refuse sampling on site The sampling method of aged refuse was designed based on the multi-layers random sampling procedure, by which closed landfill compartments used for sampling were identified into two classes (namely two layers) to represent the seasonal variation of the refuse over a year. The first layer was determined as the spring-summer refuse with higher fruit residue and the second layer as the autumn-winter refuse with much more protein food residue.Sample preparation The samples taken were screened in-situ at the landfill using a 10 mm sieve. The sample with a size less than 10 mm were then taken back to the lab and air-dried at cloudy and clean place at once. The air-dried samples were then screened using 2 mm sieve to obtain the finer fractions for research conducted in this work and manually pre-treated through taking away the wood and plant residues using wood tools such as wood hammer, wood spade, wood roller and wood board. The resultant samples were then screened using nylon sieves with 20 mesh for humic substances extraction and with 60 or 100 mesh for total organic carbon (TOC)determination.Extraction of HA and FA products The final refuse sample with 20 mesh was pre-treated by acidic elution to remove calcium in the sample, and then extracted in a 0.1 mol/L NaOH solution for 24 hours to get HA and FA mixtures. The HA was settled from the mixture solution by acidifying to pH 1-2. The modification that the 0.45 u m micro-membrane was used instead of the original ceramic filtration to remove clay colloid efficiently was carried out and obtained quite pure HA product with less than 1% of impurity. As to FA purification, some improvement on FA concentration and de-sorption method was made using adsorption resin (substitute similar to XAD-7) instead of activated carbon granular and the impurity of FA product has been decreased to around 5%.Quantitative characterization of the FA and HA products The modified soil characterization methods on humic substances were used to quantify TOC, organic-inorganic complex value and degree, and differently combined humic substances in aged-refuse. TOC determination by K^C^Oy oxidation method (heated 120 min at 105°C, recommended by Hach company) have been proved to be a more appropriate method than combustion oxidation method by TOC instrument as the former could decrease the interference caused by coal, rubber, plant residue and chemical fiber present in the aged-refuse. The TOC of aged-refuse samples increased over placement age from 5.64% to 8.49% due to the presence of high organic contents in MSW. Organic-inorganic complex value increased from 2.21% to 3.27% over the age, and the corresponding complex degree kept at around 40%, lower than the common soil value (>50%).Differently combined humic substances were separated and determined by TOC. A TOC range of 0.78-1.25% in Group I (loosely combined humic substances) and the TOC of 0.57-0.76% in Group II (stably combined humic substances) were observed to have relatively stable TOC content while Group III (tightly combined humic substances) with TOC from 0.71 to 2.70% indicated a gradual accumulation subjected to humification process.The C content either in HA or in FA products decreased by the humification process. The C, H, and N contents in HA products were higher than those in FA products, except for S content. For the vertical samples (taken at the refuse height of 0.5 m, 2 m and 4 m in the compartments) extracted from compartment closed in 1994, the HA from surface refuse had less C content than from the middle and bottom ones.Thermal analysises of HA ajjd FA products were carried on SDT Q600, which can provide simultaneous TGA and DSC curves. The heating procedure was ramp at the rate of 10°C/min to the end temperature 700 °C. Nitrogen was used as carrier gas (100 ml/min) passing through the balance and oxygen (20 ml/min) was added into the oven directly as reaction gas. The DSC curves of HA and FA were similar to those of coal since coal is the product of highly humification. Hence, a comaprison between the DSC of the humic substances obtained in this work with those of coal reported in literature were made and the corresponding messages were thus derived for the former.Spectroscopy analysis of HA and FA products FTIR spectroscopy analysis of HA and FA products provided useful information on functional radicals and structural features. Similar spectra of FA products with different age have been obtained. It seems that phenol-hydroxide, carboxyl, alkine, methyl and amino radicals, aromatic ring and aldehyde or ketone condensation plymer may be present in the FA products. Similar FTIR spectra were observed for the HA extracted from different aged refuse and the radical contents should be similar to FA products, but infrared absorbances seem to be stronger than that of FA products, showing that HA products have relatively higher proportion of aromatic ring and aldehyde or ketone condensation structure but less proportion of carboxyl radical. The FTIR spectra difference among HA products extracted from vertical samples, above mentioned, showed the relatively abundance of aromatic ring with the order of 0.5 m product>2.0 m product>4.0 m product, implying the humification process may follow the same sequence.Either HA products or FA products have similar fluorescence emission spectra with broad peak. The wavelength of peaks for HA products increased with the increase of humification age, but such a rule was not observed for FA products with fluctuating at around 450 nm. The synchronous spectra both for HA and FA products provided less information on peaks unlike the case reported by other researchers.Ultraviolet/visible spectra of HA and FA products with monotone curve gave less information on characteristic peaks. The absorbance at 200 nm was the strongest and that at 600 nm were the lowest accessing to zero. The stronger absorbance of HA products at the same wavelength than FA products reflected that the former had more aromatic and poly-phenol structures than the latter.GPC analysises The GPC analysises for FA and HA products were used toexplore the average molecular weight and molecular weight distribution. Pure water and 25mmol/L NaB^+lmmol/L Na4P2O7 were used as mobile phase for FA and HA products GPC analysis respectively. Standard curves were made using the mixture standards (Polyethylene Glycol/Oxide) with four molecular weights (460000, 25820, 1470, 106). The results showed that the weight average molecular weight (M?) of FA products ranged from 17000 to 23000 while HA products from 28000 to 66000. HA products had more polydisperse than FA products according to the ratios of Mw/Mn(over 10to 1.1).Py-GC/MS analysis Py-GC/MS is probably the optimum technology employed so far for investigating structural features of complex macromolecular materials such as humic substances although problems such as the thermal degradation of building blocks, secondary reactions, still exist. In this work for HA and FA, over 100 main pyrolysis products had been detected by GC/MS after pyrolysis, which can be classified into four types of original resources: polysaccarides, proteins, lignins and lipids. By calculating the relative abundance of five types of pyrolysis products, N-containing compounds, aliphatic products, lignin products, carbohydrate products and aromatic products, it has been found that the relative abundance of carboxyl radical with 6 and 7 year-old were higher than those of the other ages. As the refuse ages extend, aromatic products increased over the humification process while lignin products decreased accordingly.Heavy metals pollution assessments and their bio-availability for aged-refuse Heavy metals pollution assessments for aged-refuse samples were carried out based on the total value and non-residue value respectively. Zinc pollution has been highlighted among six heavy metal of interest: Zn, Pb, Ni, Cr, Cu, Cd. According to traditional assessment method, the aged-refuse should be 5-8 times over the value of Level II Soil Environmental Standards and 3-5 times over the value of Level III. The residue-phase zinc may be considered safe and impossibly eluted under natural soil environment. Hence, the aged-refuse could be considered to reach the Level III but slightly beyond Level II.Bio-availability of heavy metals in aged-refuse was studied by in-situ aged-refuse-aspen ecological system in Shanghai Refuse Landfill. The distributions of six heavy metals in various aspen positions, leaves, stems and roots, had been measured and the results showed that zinc accumulation was quite obvious. Typically, zinc contents in the southern leaves reach 25 times over the control sample.Zinc in the non-residue phase can be referred as to the active zinc value indicating its transfer and accumulation in aspen. The relative coefficients between non-residue phase zinc in aged-refuse and zinc concentration in leaves were 0.5914, 0.4829, 0.2897 for top, southern and northern leaves respectively. However, the zinc concentrations in the stems appeared to have less dependence on the non-residue zinc in the aged-refuse, in contrast with those in root with a relative coefficient of 0.7338.Zinc both in carbonate phase and in organically bound phase showed less dependence on the zinc content in various aspen positions, but exchangeable phase and bound to oxide phase of zinc in aged-refuse showed a close relationship with zinc content in aspen leaves, with the highest relative coefficient (0.8772) between the exchangeable zinc and top aspen leaves, indicating that the zinc transferring and accumulating from aged-refuse towards aspen should be attributed to zinc in exchangeable phase and bound to oxide phase.
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