In-Situ Catalytic Gasification of Rice Hull Using Municipal Solid Waste Incineration Bottom Ash.

The demand for alternative energy is increasing rapidly because of global warming and the depletion of fossil fuels. Gasification is a technology that produces gaseous fuels through the incomplete combustion of waste or biomass. The introduction of a catalyst during gasification may increase the production of H2 and reduce tar formation. In this study, the catalytic gasification of rice hulls was carried out using a fluidized gasifier. To improve the gas yield and reduce tar, municipal solid waste incineration bottom ash (IBA) having nanoporosity was introduced as a substitute for the fluidized bed material. Gasification was carried out at 800 °C, and the flow materials were silica sand, dolomite, and incineration bottom ash. The equivalence ratio, which is the ratio of oxygen supplied to oxygen required for complete combustion, was set to 0.3. The application of alternate fluidized bed materials (dolomite and incineration bottom ash) was effective in improving the hydrogen yield and tar reduction. This was attributed to the high Ca and Mg contents in dolomite and incineration bottom ash. Therefore, it is expected that IBA can be utilized as a catalytic fluidized bed material to replace silica sand.

Catalytic Pyrolysis of Seawater Aged Polypropylene Over HZSM-5, HY, and Al-MCM-41.

The effect of seawater aging on the thermal and catalytic pyrolysis of polypropylene (PP) was investigated using a thermogravimetric analyzer and pyrolyzer-gas chromatography/mass spectrometry. Although the surface properties of PP were of the oxidized form by seawater aging, the decomposition temperature and non-catalytic pyrolysis products of PP were relatively unchanged largely due to seawater aging. The catalytic pyrolysis of seawater-aged PP over all the catalysts produced smaller amounts of aromatic hydrocarbons than that of fresh PP due to catalyst poisoning caused by the residual inorganics. Among the catalysts, microporous HZSM-5 (SiO2/Al2O3:23) produced the largest amount of aromatic hydrocarbons followed in order by microporous HY(30) and nanoporous Al-MCM-41(20) from seawater-aged PP due to the high acidity and appropriate pore size for the generation of aromatic hydrocarbons.

Evaluation of error inducing factors in unmanned aerial vehicle mounted detector to measure fugitive methane from solid waste landfill.

Many methods have been applied to monitor fugitive methane gas from landfills. Recently, there have been suggestions to use a framework utilizing an unmanned aerial vehicle (UAV) for landfill gas monitoring, and several field campaigns have proved that a rotary UAV-based measurement has advantages of ease of control and high-resolution concentration mapping on the target planes. However, research on the evaluation of error-inducing factors in the suggested system is limited so far. This study prepared a measurement system with a lightweight methane detector and a rotary UAV to support the applicability of rotary UAV in landfill gas monitoring. Then, the validity of the system was tested experimentally and theoretically. In the detector reliability test, the methane detector had sufficient resolution for field application. The critical UAV velocity required was obtained to ensure the credibility of the proposed measurement system. When spatial interpolators were applied to field data from the measurement system, the empirical Bayesian kriging demonstrated the best prediction of methane concentrations at unmeasured points. With the verifications provided in this study, this proposed method may contribute to reducing uncertainty in estimating fugitive landfill gas emission.

Incorporating interaction terms in multivariate linear regression for post-event flood waste estimation.

Multivariate linear regression methodology has been conceived as a viable technique in flood waste estimation. The fundamental assumption of the conventional flood waste model, independence between input variables, may not work in reality. As an alternative, we evaluated the effectiveness of including interaction terms in flood waste modeling. The secondary objectives include to suggest the strategy in flood waste mitigation and to explore a plausible explanation to the modeling results. In the scheme of model development and assessment, ninety flood cases in South Korea were statistically analyzed. Input variables for regression analysis were selected from available datasets in the national disaster information system and the selected variables were flood damage variables used to quantify the amount of flood waste. According to the results, incorporating the interaction terms improved the estimation accuracy of the model. The single-variable sensitivity analysis revealed that mitigating damage to rivers and croplands would most efficiently reduce potential flood waste generation. The interaction terms appeared to compensate for the over/underestimated waste amounts by single terms, and they explained the nonlinear response of waste generation. Observations made throughout the field survey revealed that the nonlinear and interactive pattern of flood waste generation corresponded to the results from the regression analysis. In a practical aspect, incorporating the interaction terms would be an effective method to enhance the flood waste estimation model without costly works for further variables exploration.

Fate of chlortetracycline antibiotics during anaerobic degradation of cattle manure.

As veterinary antibiotics (VAs) cause adverse effects on nature, anaerobic digestion (AD) of livestock manure has been receiving attention as an exposure route of VAs. This research evaluated the anaerobic degradation and phase distribution of chlortetracycline (CTC) with its epimer (4-epi-CTC, ECTC) and isomer (Iso-CTC, ICTC). In addition, whether CTC can inhibit not only AD of a substrate but also the degradation of CTC was assessed. Anaerobic batch assays were performed with cattle manure for 30 days by varying the initial concentration of CTC; 0, 10, 25, 50, and 100 mg/L. Approximately 25-43 % (w/w) of CTC was primarily degraded while 18-25 % and 20-26 % of CTC was transformed into ECTC and ICTC, respectively. Up to 88 % (w/w) of the remaining CTC, ECTC, and ICTC was present in the solid phase. In addition, CTC inhibited not only the mineralization of the cattle manure but also the degradation of CTC due to co-metabolism. In conclusion, significant quantities of CTC, ECTC, and ICTC can be exposed to nature by solid phase of anaerobic digestate. The inhibition on AD can reduce the degradation of CTC, ECTC, and ICTC during the AD.

Removal of aqueous-phase Pb(II), Cd(II), As(III), and As(V) by nanoscale zero-valent iron supported on exhausted coffee grounds.

Nanoscale zero-valent iron (NZVI) is recognized as an excellent adsorbent for metallic contaminants. Nevertheless, NZVI itself tends to agglomerate, so that its performance deterioriates without supporting materials. The use of exhausted coffee grounds as a supporting material for NZVI is expected to resolve this problem and provide the social benefits of waste minimization and resource recycling. In this study, NZVI was supported on exhausted coffee grounds (NZVI-Coffee ground) to enhance its dispersion. The aims of this study were to characterize NZVI-Coffee ground with a focus on atomic dispersion, evaluate NZVI-Coffee ground as an adsorbent for typical metallic contaminants and arsenic, and assess the effects of solution chemistry on the adsorption process. In order to achieve these goals, characterization, adsorption kinetics, adsorption equilibrium, and the effects of pH and temperature on adsorption were studied. Pb(II), Cd(II), As(III), and As(V) were selected as target contaminants. The characterization study showed that atomic dispersion was enhanced four-fold by supporting NZVI on coffee grounds. The enhanced dispersion resulted in rapid kinetic characteristics and large adsorption capacity. The optimum pH for adsorption of Pb(II) and Cd(II) was 4-6, and that for As(III) and As(V) was 2-4. The pH effect can be explained by surface protonation/deprotonation and adsorbate speciation. Only the adsorption of Pb(II) was an exothermic process; those of other species were endothermic. In every tested case, the adsorption process was spontaneous. According to the results, NZVI-Coffee ground is an effective adsorbent for the removal of aqueous phase Pb(II), Cd(II), As(III), and As(V).

Innovation of flux chamber network design for surface methane emission from landfills using spatial interpolation models.

Solid waste landfills are one of the primary anthropogenic sources of methane emissions which are often estimated by flux chamber measurements on landfill surfaces. Due to the small footprint of the flux chamber on the surface coverage, however, it is important to design a proper spatial deployment of the chambers with an optimal number of measurement points such that the measured fluxes are correctly scaled up to the whole landfill area. In order to improve the design of flux chamber network, several deterministic interpolation models were applied and results of reproducibility tests with 22 flux measurement data sets from ten municipal solid waste landfills in the Republic of Korea were compared one another. The bilinear model and natural neighbor model among the deterministic models showed stable results in all cases. The surface methane emissions estimated from arithmetic or geometric mean resulted in significant under- or overestimation compared to spatial interpolation methods in all data sets. As a result of this study, minimal number of flux measurement points could be determined for target error levels. Innovative flux chamber network design with proper measurement points will improve the accuracy of methane emission estimate from solid waste landfills.

Field measurement of greenhouse gas emissions from biological treatment facilities of food waste in Republic of Korea.

The Republic of Korea is trying to reduce greenhouse gas emissions by 37% from business-as-usual levels by 2030. Reliable greenhouse gas inventory is prerequisite to making effective greenhouse gas reduction plans. Currently, Intergovernmental Panels on Climate Change default emission factors were used in biological treatment of the solid waste sector without any consideration of the biological treatment process in the Republic of Korea. In this study, greenhouse gas emissions from biological treatment facilities of food waste have been monitored in order to develop country-specific emission factors in the Republic of Korea. Greenhouse gas emissions were monitored in two composting facilities and one anaerobic digestion facility. All study sites possess a local exhaust ventilation system and odour treatment system. Continuous greenhouse gas monitoring has been conducted on gathered gases using a non-dispersive infrared detector before entering odour treatment systems. At composting facilities, the emission factors of CH4 and N2O were 0.17-0.19 g-CH4 kg-waste-1 and 0.10-0.13 g-N2O kg-waste-1, respectively. Especially, the emission factors of CH4 in composting facilities showed significantly low values compared with other countries owing to the air blowing by a pump at the studied sites. At anaerobic digestion facilities, the emission factors of CH4 and N2O were 1.03 g-CH4 kg-waste-1 and 0.53 g-N2O kg-waste-1. The emission factors estimated in this study showed a significant difference from the Intergovernmental Panels on Climate Change default value. Therefore, it is recommended to develop a country-specific emission factor in order to reflect the different processes of biological treatment of solid waste.

Field assessment of semi-aerobic condition and the methane correction factor for the semi-aerobic landfills provided by IPCC guidelines.

According to IPCC guidelines, a semi-aerobic landfill site produces one-half of the amount of CH4 produced by an equally-sized anaerobic landfill site. Therefore categorizing the landfill type is important on greenhouse gas inventories. In order to assess semi-aerobic condition in the sites and the MCF value for semi-aerobic landfill, landfill gas has been measured from vent pipes in five semi-aerobically designed landfills in South Korea. All of the five sites satisfied requirements of semi-aerobic landfills in 2006 IPCC guidelines. However, the ends of leachate collection pipes which are main entrance of air in the semi-aerobic landfill were closed in all five sites. The CH4/CO2 ratio in landfill gas, indicator of aerobic and anaerobic decomposition, ranged from 1.08 to 1.46 which is higher than the values (0.3-1.0) reported for semi-aerobic landfill sites and is rather close to those (1.0-2.0) for anaerobic landfill sites. The low CH4+CO2% in landfill gas implied air intrusion into the landfill. However, there was no evidence that air intrusion has caused by semi-aerobic design and operation. Therefore, the landfills investigated in this study are difficult to be classified as semi-aerobic landfills. Also MCF of 0.5 may significantly underestimate methane emissions compared to other researches. According to the carbon mass balance analyses, the higher MCF needs to be proposed for semi-aerobic landfills. Consequently, methane emission estimate should be based on field evaluation for the semi-aerobically designed landfills.