Kelvin Tsun Wai Ng

Empirical modeling of heavy metal extraction by EDDS from single-metal and multi-metal contaminated soils

The effectiveness of using biodegradable EDDS (S,S-ethylenediaminedisuccinic acid) for metal extraction has drawn increasing attention in recent years. In this study, an empirical model, which utilized the initial metal distribution in soils and a set of parameter values independently determined from sequential extraction, was developed for estimating the time-dependent heavy metal extraction by EDDS from single-metal and multi-metal contaminated soils. The model simulation provided a satisfactory description of the experimental results of the 7-d extraction kinetics of Cu, Zn, and Pb in both artificially contaminated and field-contaminated soils. Thus, independent and prior assessment of extraction efficiency would be available to facilitate the engineering applications of EDDS. Furthermore, a simple empirical equation using the initial metal distribution was also proposed to estimate the extraction efficiency at equilibrium. It was found that, for the same type of soils, higher extraction efficiency was achieved in multi-metal contaminated soils than in single-metal contaminated soils. The differences were 4-9%, 9-16%, and 21-31% for Cu, Zn, and Pb, respectively, probably due to the larger proportion of exchangeable and carbonate fractions of sorbed Zn and Pb in multi-metal contaminated soils. EDDS-promoted mineral dissolution, on the other hand, was more significant in multi-metal contaminated soils as a result of the higher EDDS concentration applied to the soils of higher total metal content.

Coalescence/Filtration of an Oil-In-Water Emulsion in an Immobilized Mucor rouxii Biomass Bed

Breakdown mechanisms and flow characteristics involved in an immobilized M. rouxii biomass bed treating oil-in-water emulsion were investigated. The purpose of this research was to evaluate the applicability of the well-known Carman-Kozeny filtration equation to a 1000 mm immobilized M. rouxii biomass bed treating a standard mineral oil-in-water emulsion at six different flow rates (12, 16, 20, 24, 28, and 32 mL/min). The specific permeability coefficient, the Carman-Kozeny constant, and the shape factor of immobilized M. rouxii bed were found to be 2.135 × 10−8 m2, 5.03, and 1.13, respectively. The coalescence efficiency decreased with an increase in bed depth (from 15.9% at 200 mm to 4.0% at 1000 mm depth for a flow rate of 12 mL/min). Results indicated possible sequential occurrence of coalescence and filtration in the immobilized M. rouxii biomass bed.

Mechanical behaviors of a synthetic paste of tire chips and paper sludge in MSW landfill daily cover applications

A waste-derived paste of a mixture of paper sludge and tire derived aggregate (TDA) was investigated for daily cover application in municipal solid waste (MSW) landfills. The use of earth materials as daily covers not only consumes valuable landfill space, but also creates a series of operating issues. In this study, an experimental testing program was undertaken with the goal of evaluating the mechanical behaviors of the paste based on the findings of the index properties, compressibility, hydraulic conductivity, stress-induced deformation, stress–strain response, and shear resistance of the materials. The mechanical behaviors of the individual TDA, the sludge, as well as the mixture of the two, were evaluated. When compared to traditional soil covers, the proposed paste was: (i) 2–3 times lighter in weight; (ii) at least two orders of magnitude more impermeable; and (iii) comparable in shear resistance. It was also found that with the addition of TDA to the sludge, the shear strength of the paste was im...

Optimization of first order decay gas generation model parameters for landfills located in cold semi-arid climates

Canada has one of the highest waste generation rates in the world. Because of high land availability, land disposal rates in the province of Saskatchewan are high compared to the rest of the country. In this study, landfill gas data was collected at semi-arid landfills in Regina and Saskatoon, Saskatchewan, and curve fitting was carried out to find optimal k and Lo or DOC values using LandGEM, Afvalzorg Simple, and IPCC first order decay models. Model parameters at each landfill were estimated and compared using default k and Lo or DOC values. Methane generation rates were substantially overestimated using default values (with percentage errors from 55 to 135%). The mean percentage errors for the optimized k and Lo or DOC values ranged from 11.60% to 19.93% at the Regina landfill, and 1.65% to 10.83% at the Saskatoon landfill. Finally, the effect of different iterative methods on the curve fitting process was examined. The residual sum of squares for each model and iterative approaches were similar, with the exception of iterative method 1 for the IPCC model. The default values in these models fail to represent landfills located in cold semi-arid climates. The use of site specific data, provided enough information is available regarding waste mass and composition, can greatly help to improve the accuracy of these first order decay models.

Alternative carbon dioxide modelling approaches accounting for high residual gases in LandGEM

High Canadian waste disposal rates necessitate landfill gas monitoring and accurate forecasting. CO2 estimates in LandGEM version 3.02 currently rest on the assumptions that CO2 is a function of CH4, where the two gases make up nearly 100% of landfill gas content, leading to overestimated CO2 collection estimates. A total of 25 cases (five formulas, five approaches) compared annual CO2 collection at four western Canadian landfills. Despite common use in literature, the 1:1 ratio of CH4 to CO2 was not recommended to forecast landfill gas collection in cold climates. The existing modelling approach significantly overestimated CO2 production in three of four sites, resulting in the highest residual sum of squares. Optimization resulted in the most accurate results for all formulas and approaches, which had the greatest reduction in residual sums of squares (RSS) over the default approach (60.1 to 97.7%). The 1.4 Ratio approach for Lo:Lo-CO2 yielded the second most accurate results for CO2 flow (mean RSS reduction of 50.2% for all sites and subsection models). The annual k-modified LandGEM calculated k’s via two empirical formulas (based on precipitation) and yielded the lowest accuracy in 12 of 20 approaches. Unlike other studies, strong relationships between optimized annual k’s and precipitation were not observed.

Fines migration from soil daily covers in Hong Kong landfills

Laboratory tests using 240 mm diameter columns were conducted to study fines migration in conditions that simulate daily soil covers in Hong Kong municipal solid waste landfills. Five factors suspected to affect fines migration were examined: moisture content at soil compaction, overburden pressure, pumping rate, cover thickness, and soil-waste interface condition. The results show that moisture content at compaction, cover thickness, and soil-waste interface are the most influential parameters on fines migration in completely decomposed granite daily covers. The measured equivalent sizes of migratory fines from the soil covers were in the range of 4-140 μm. The majority of migratory fines migrated during first permeations, representing 64-86% of the total by mass. Larger particles tended to migrate from the soil mass during the saturation process. In a typical run, about 0.0018% of the total cover soil (by dry weight) was washed out during a typical 1h rainfall event. The results of the laboratory studies point to important engineering implications on the operation of local MSW landfills regarding the use of sandy daily covers.

Effects of Design Mix and Porosity of Waste-Derived Paste as Landfill Daily Covers on Lead Retardation

An innovative waste-derived paste of waste tire chips and paper sludge was proposed for daily cover applications in municipal solid waste landfills. In this study, retardation and transport behaviors of lead (Pb) by the proposed paste were investigated using column tests. Breakthrough curves of 16 specimens at various design mixes and porosities were presented. A one-dimensional equilibrium deterministic transport model was used to fit the transport parameters from the breakthrough curves and to verify the homogeneity of the specimens. Analysis of the effluent concentrations from the column tests displayed a retardation effect for Pb in all cases, with fitted retardation factors ranging from 19.9 to 59.0. Lead retardation by the proposed paste was found to be sensitive to the paste’s porosity and design mix. Early arrivals of solute were observed unexpectedly in columns with high paper sludge content under high packing densities and were attributed to the possible presence of preferential flow paths. The ...