Huayong Wu

Environmental impact assessment of solid waste management in Beijing City, China

The environmental impacts of municipal solid waste management in Beijing City were evaluated using a life-cycle-based model, EASEWASTE, to take into account waste generation, collection, transportation, treatment/disposal technologies, and savings obtained by energy and material recovery. The current system, mainly involving the use of landfills, has manifested significant adverse environmental impacts caused by methane emissions from landfills and many other emissions from transfer stations. A short-term future scenario, where some of the landfills (which soon will reach their capacity because of rising amount of waste in Beijing City) are substituted by incinerators with energy recovery, would not result in significant environmental improvement. This is primarily because of the low calorific value of mixed waste, and it is likely that the incinerators would require significant amounts of auxiliary fuels to support combustion of wet waste. As for the long-term future scenario, efficient source separation of food waste could result in significant environmental improvements, primarily because of increase in calorific value of remaining waste incinerated with energy recovery. Sensitivity analysis emphasized the importance of efficient source separation of food waste, as well as the electricity recovery in incinerators, in order to obtain an environmentally friendly waste management system in Beijing City.

Evaluation of the biological stability of waste during landfill stabilization by thermogravimetric analysis and Fourier transform infrared spectroscopy.

This study seeks to assess the biological stability of landfilled municipal solid waste (MSW) based on the changes in organic matter, as revealed by thermogravimetric analysis and Fourier transform infrared (FTIR) spectroscopy. Derivate thermogravimetry profiles (DTG) showed a reduction in peak intensity at 200-350 °C (DTG2), while an increase in peak intensity and a shift towards higher temperature at 400-600 °C (DTG3). The decrease in the peak intensity of the aliphatic methylene at 2920 and 2850 cm(-1), and the increase of aromatic substances and polysaccharide at 1640 cm(-1) in the FTIR spectra also confirm the changes. Well-fitted correlations of the peak intensity ratio (2920/1640) and peak area ratio (DTG2/DTG3) to C/N ratio were also established, confirming that the 2920/1640 and the DTG2/DTG3 ratios can be considered as reliable parameters for tracking the biological stability of MSW during landfill stabilization.

Adsorption of mixed cationic-nonionic surfactant and its effect on bentonite structure.

The adsorption of cationic-nonionic mixed surfactant onto bentonite and its effect on bentonite structure were investigated. The objective was to improve the understanding of surfactant behavior on clay mineral for its possible use in remediation technologies of soil and groundwater contaminated by toxic organic compounds. The cationic surfactant used was hexadecylpyridinium bromide (HDPB), and the nonionic surfactant was Triton X-100 (TX100). Adsorption of TX100 was enhanced significantly by the addition of HDPB, but this enhancement decreased with an increase in the fraction of the cationic surfactant. Part of HDPB was replaced by TX100 which decreased the adsorption of HDPB. However, the total adsorbed amount of the mixed surfactant was still increased substantially, indicating the synergistic effect between the cationic and nonionic surfactants. The surfactant-modified bentonite was characterized by Brunauer-Emmett-Teller specific surface area measurement, Fourier transform infrared spectroscopy, and thermogravimetric-derivative thermogravimetric/differential thermal analyses. Surfactant intercalation was found to decrease the bentonite specific surface area, pore volume, and surface roughness and irregularities, as calculated by nitrogen adsorption-desorption isotherms. The co-adsorption of the cationic and nonionic surfactants increased the ordering conformation of the adsorbed surfactants on bentonite, but decreased the thermal stability of the organobentonite system.

Fluorescence-based rapid assessment of the biological stability of landfilled municipal solid waste.

Fluorescence Excitation-Emission Matrix (EEM) combined with fluorescence regional integration (FRI) and parallel factor analysis (PARAFAC) was employed to tracing the properties and behavior of the water-execrable organic matter (WEOM) from landfilled municipal solid waste (MSW) for assessing the biological stability. The 3-components PARAFAC model developed showed the WEOM dominated by two humic-like materials (components C1 and C2) which were highly correlated and behave similarly in this work, and a protein-like material (component C3). The percent fluorescence response P(i,n) from FRI and maximum fluorescence intensity F(max) of the components from PARAFAC proved to be sensitive indicators of the bulk properties and transformation of WEOM during landfill stabilization. C1/C3 F(max) ratio was found to be the most sensitive indicator of the biostablization state of the landfilled MSW and can be considered a reliable parameter. These results reveal that EEM-PARAFAC/FRI enabled a rapid and accurate assessment of biological stability of landfilled MSW.

Evolution of unsaturated hydraulic properties of municipal solid waste with landfill depth and age.

Successful modeling of liquid and air flow and hence designing of liquid and air addition systems in the landfills are constrained by the lack of key parameters of unsaturated hydraulic properties of municipal solid waste (MSW), which are strongly dependent on the depth of burial and the degree of decomposition. In this study, water retention curves (WRC) of MSW are measured using pressure plate method on samples repacked according to the in situ unit weight measured during borehole sampling, representing the MSW in shallow, middle, and deep layers. The measured WRC of MSW is well-reproduced by the van Genuchten-Mualem model, and is used to predict the unsaturated hydraulic properties of MSW, including water retention characteristics and unsaturated hydraulic conductivity. The estimated model parameters are consistent with other studies, suggesting that the pressure plate method yields reproducible results. As the landfill depth and age increase, the overburden pressure, the highly decomposed organic matter and finer pore space increase, hence the capillary pressure increases, causing increases in air-entry values, field capacity and residual water content, and decreases in steepness of WRC and saturated water content. The unsaturated hydraulic properties of MSW undergo changes with landfill depth and age, showing more silt loam-like properties as the landfill age increases.

Optimization of supercritical phase and combined supercritical/subcritical conversion of lignocellulose for hexose production by using a flow reaction system.

A flow reaction system was utilized to investigate lignocellulose conversion using combined supercritical/subcritical conditions for hexose production. Initially, investigation of cellulose hydrolysis in supercritical water and optimization of reaction parameters were done. Oligosaccharide yields reached over 30% at cellulose concentrations of 3-5 gL(-1) and reaction times of 6-10s at 375 °C, and 2.5-4 gL(-1) and 8-10s at 380 °C. Temperatures above 380 °C were not appropriate for the supercritical phase in the combined process. Subsequently, conversion of lignocellulosic materials under combined supercritical/subcritical conditions was studied. Around 30% hexose was produced from corn stalks under the optimal parameters for supercritical (380 °C, 23-24 MPa, 9-10s) and subcritical (240 °C, 8-9 MPa, 45-50s) phases. Flow systems utilizing the combined supercritical/subcritical technology present a promising method for lignocellulosic conversion. The results of this study provide an important guide for the operational optimization and practical application of the proposed system.

Field air permeability and hydraulic conductivity of landfilled municipal solid waste in China

The successful design and operation of in situ treatment systems using air and water additions for sustainable landfilling are constrained by a lack of knowledge of the key parameters, such as field air permeability and hydraulic conductivity of landfilled municipal solid waste (MSW). This work provides data on the field air permeability k(a) and hydraulic conductivity K(w) of MSW obtained by conducting short-term air and water injection tests at a landfill in Beijing, China. The k(a) and K(w) values are found to in the range of 1.2 × 10(-13)-1.9 × 10(-12) m(2) and 5.9 × 10(-7)-7.2 × 10(-6) m s(-1), respectively. Both k(a) and K(w) decreased significantly with landfill depth due to the increase in overburden pressure and the finer particles of the waste in deeper layers, leading to a lower porosity of waste. The higher moisture saturation in the deeper layers also contributed to the decrease in k(a). To compare the permeability with respect to air and water, the water permeability k(w) was calculated based on the estimated K(w) and was found to be approximately three orders of magnitude smaller than the corresponding k(a) for waste at the same layer. The differences in k(w) and k(a) may be due to the relative air permeability, the potential short-circuiting of air and active production of biogas, which undermine the relationship between k(w) and k(a). Therefore, to successfully design and operate air and water addition systems in a landfill, in situ measurements of the air permeability and hydraulic conductivity are essential.

Enhanced photodegradation of pentachlorophenol by single and mixed cationic and nonionic surfactants.

The photocatalytic degradation of pentachlorophenol (PCP) using a TiO(2) catalyst in a surfactant-containing system was investigated. PCP abatement by photocatalysis was significantly enhanced by the addition of cationic and nonionic surfactants, both single and mixed, at appropriate concentrations. The enhanced photodegradation can be mainly attributed to the formation of admicelles on the TiO(2) surface. This phenomenon can lead to the incorporation of more PCP, thereby providing TiO(2) with remarkably higher capture rates for target pollutants. Hence, PCP was rendered easily available to photo-yielded oxidative radicals on the catalyst surface. Notably, mixed cationic-nonionic surfactants yielded much higher photodegradation efficiencies than the corresponding single surfactants, indicating the existence of a synergistic effect in the complex system. The adsorption behavior of PCP on TiO(2) in the surfactant solutions was investigated to elucidate this synergism. Fourier-transform infrared (FTIR) spectroscopy was adopted to gain insight into the structural changes induced by the surfactants and a better understanding of the surfactant-assisted photocatalytic degradation mechanism was obtained.

Stepwise superposition approach for the analytical solutions of multi-dimensional contaminant transport in finite- and semi-infinite aquifers

Analytical solutions of contaminant transport in multi-dimensional media are significant for theoretical and practical purposes. However, due to the problems for which the solutions are sought which are complex in most of the cases, most available analytical solutions in multi-dimensional media are not given in their closed forms. Integrals are often included in the solution expressions, which may limit the practitioners to use the solutions. In addition, available multi-dimensional solutions for the third-type sources in bounded media are fairly limited. In this paper, a stepwise superposition approach for obtaining approximate multi-dimensional transport solutions is developed. The approach is based on the condition that the one-dimensional solution along the flow direction is known. The solutions are expressed in their closed forms without integrals. The transport media to the solutions are flexible and can be finite, semi-infinite, or infinite in the transverse directions. The solutions subject to the first- and third-type boundary conditions at the inlet with a distributed source over the domain are obtained. The integrals in some known solutions can also be evaluated by the approach if they can be derived to include known longitudinal integrals with respect to time. The accuracy and efficiency of the solutions proposed in this paper are verified through test problems and calculation examples.