James O. Leckie - Academia.edu (original) (raw)

Papers by James O. Leckie

Limnology and Oceanography, Mar 1, 1985

References BEER, T. 1982. Environmental oceanography. An introduction to the behaviour of coastal... more References BEER, T. 1982. Environmental oceanography. An introduction to the behaviour of coastal waters. Pergamon. CSANADY, G. T. 1982. Circulation in the coastal ocean. Reidel.

Waste Management & Research, Oct 1, 1996

A mathematical model for the generation and transport of gas and heat in a sanitary landfill was ... more A mathematical model for the generation and transport of gas and heat in a sanitary landfill was developed based on earlier work on the Mountain View Controlled Landfill Project (MVCLP) in California, U.S.A. The present model incorporates biokinetic model equations describing the dynamics of the microbial landfill ecosystem into multi-layer, time-dependent transport and generation of gas and heat models. It

Proceedings of the Water Environment Federation, 2005

In many cases, "knowing how little you know" is an important part of decision-making under uncert... more In many cases, "knowing how little you know" is an important part of decision-making under uncertainty. In the case of mercury TMDLs in mercury/gold mine impacted watersheds, it is well understood that large uncertainties exist in estimates of the various mercury source loadings, predictions of methyl mercury formation and bioaccumulation in fish, and other predictions made in the TMDL linkage analysis. Current linkage analysis practice often involves the use of deterministic models in series, with the outputs from one model being used as inputs into another deterministic model. Uncertainty is often "handled" through the use of safety factors in environmental targets and/or the use of ad hoc uncertainty estimates. In practice, these ad hoc uncertainty estimates may have little influence in the actual decision-making process. The work reported here is part of a larger effort to demonstrate a probabilistic approach that treats uncertainty as risk to be managed in the decision-making process (Labiosa et al., 2005; Labiosa et al., 2003).

Environmental Science & Technology, Nov 1, 1981

Water Resources Research, Aug 1, 2000

Suspended particles are a ubiquitous component of aqueous environments and are found over broad r... more Suspended particles are a ubiquitous component of aqueous environments and are found over broad ranges of size and density. Particle transport and fate have an important role in the regulation of contaminants and nutrients in natural settings. The mechanisms that control the transport and size of particulate material in solution also play a fundamental role in the successful operation of engineered systems, such as sedimentation ponds and flocculation tanks, as well as flotation and filtering reactors. Adequate modeling of particle transport and aggregation is required for better understanding and prediction of the effects of particulate material in natural aqueous systems, as well as for designing efficient physicochemical processes to deal with suspended solids. In this paper we illustrate how numerical diffusion produced by the use of first-order finite difference schemes can introduce significant errors in the modeling of particle settling in quiescent systems and how this error is compounded when aggregation is considered. To model settling without introducing numerical diffusion, while preserving numerical efficiency, we propose the residence-time scheme, a simple numerical scheme based on the residence time of each size fraction in the elements of the spatial discretization. For the solution of the settling-aggregation equation the alternatingoperator-splitting technique (AOST) is used. The inherent modularity and simplicity of AOST allows smooth incorporation of additional particle transport mechanisms such as mixing, advection, etc.

Chemical speciation of trace metals in aqueous systems is determined by a variety of competitive ... more Chemical speciation of trace metals in aqueous systems is determined by a variety of competitive reactions. Sediments act as sinks for many trace elements, forming surface complexes and otherwise surface-related compounds. Reactions between dissolved trace metals and functional groups at sediment surfaces can be described as coordination reactions similar to those occurring in solution. Factors inherent to both sediment and solution influence the trace metal speciation. These factors include pH, type of mineral, surface area and/or density of reactive surface sites, complexing ligands, and competing ions. The relative importance of some of these factors was studied using an isotope dilution technique. Coastal sediment samples from the Gulf of Mexico were used as the solid matrix. Models developed for pure minerals were used here to (empirically) describe the complex assemblages of minerals in the natural sediment samples.

Springer eBooks, 1986

Group discussions were limited to metals and certain metalloids, except that N, P, and S were con... more Group discussions were limited to metals and certain metalloids, except that N, P, and S were considered in the broader topic of biogeochemical cycles. In many instances, the statements concerning metals are also applicable to many, or even most, other elements. However, our discussions were focused on the metals and metalloids because of their major importance as environmental pollutants.

Occupational Health and Industrial Medicine, 1998

Thii report was prepared as an account of work sponsored by an agency of the United States Govern... more Thii report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, reammendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Water Research, Apr 1, 2000

ÐAggregation and sedimentation of particles in lakes, estuaries, settling basins and the deep oce... more ÐAggregation and sedimentation of particles in lakes, estuaries, settling basins and the deep ocean play a central role in biological cycles, fate and movement of contaminants, and trace element transport. Relative quiescence with continuous in¯ux characterizes these and other aqueous environments. However, our understanding of the processes of aggregation and sedimentation in these vital systems is poor. Inadequate experimental systems and measuring instrumentation are primary causes of this shortcoming. This paper details a laboratory experimental system which creates a continuous¯ow, quiescent microcosm in which particle aggregation and settling can be studied. The system's functioning and quiescence has been rigorously veri®ed and the conditions for successful operation de®ned. A model is detailed which describes¯uid and solute movement in the experimental system. The results of the system veri®cation studies indicate signi®cant¯uid mixing may occur in experimental systems which are assumed to be quiescent, yet where no careful temperature management has been employed. This unexpected and uncontrolled¯uid motion may lead to signi®cant errors in experiments whenever particles smaller than about 20 microns with environmentally relevant densities are studied.

Applied Geochemistry, 1988

Journal of Membrane Science, Dec 1, 2010

Bromate is suspected to be a carcinogenic compound with a maximum contaminant level in drinking w... more Bromate is suspected to be a carcinogenic compound with a maximum contaminant level in drinking water imposed by the USEPA at 0.010 mg/L. The removal of bromide and bromate anions by hybrid coagulation-nanofiltration technique was systematically investigated in this study where humic acid (HA) was used as the model NOM. Two types of membranes (NF-270 and NF-90) and two types of coagulants (alum and ferrous sulphate) were investigated with regard to humic acid, bromide and bromate removals as well as the permeate flux decline and quality. It was found that bromide could not be effectively removed by nanofiltration, coagulation, or hybrid coagulation-nanofiltration, whereas bromate was reduced to bromide when ferrous sulphate was used. In addition to reducing bromate, humic acid was effectively removed by this technique while the permeate flux was maintained and in some cases improved, which suggests that the technique has some potentials to be applied in drinking water treatment train. Since coagulation and membrane filtration have been widely applied in drinking water treatment, the experimental results of this study indicate that the high removal rate of bromate in current water treatment processes can be achieved by simple modification of treatment processes and selection of proper coagulant.

Water Practice and Technology, 2006

Complete sludge retention MBR appears to be an innovative technology which no sludge will be prod... more Complete sludge retention MBR appears to be an innovative technology which no sludge will be produced, hence eliminating the sludge disposal cost. However, the understanding of microbial behaviour in the complete sludge retention MBR was still not adequately established. This study was conducted to investigate the biological performances and microbial behaviour of three different SRT MBRs (5 days SRT, 10 days SRT and prolonged SRT). The results revealed that membrane filtration assisted for maintaining the high degree of organic removal (above 97%) for all MBRs. High organic degradation was noticed in the prolonged SRT MBR (89.44%) compared with 5 days SRT (77.64%) and 10 days SRT (85.62%) MBRs. This showed that the prolonged SRT MBR posed a greater capability for further degradation of inert organics and SMP. Extremely low sludge yield (0.0388 g VSS/g COD) was occurred in the prolonged SRT condition compared with 5 and 10 days SRT conditions. The low SOUR did not affect the degrada...

Adsorption of Metals by Geomedia, 1998

... These observations lead to some hypotheses concerning the interactions be-tween a multidentat... more ... These observations lead to some hypotheses concerning the interactions be-tween a multidentate organic ligand ... molecule, the orientation of citrate on a nonhomogeneous surface (ie, with multiple crystal faces ... The effect of citrate on adsorption of UO|+ to goethite would be con ...

Proceedings of the 4th International Symposium on Environmental Hydraulics & 14th Congress of Asia and Pacific Division, International Association of Hydraulic Engineering and Research, 15-18 December 2004, Hong Kong, 2004

Desalination, Apr 1, 2007

High strength industrial wastewater was treated using a pilot scale submerged membrane bioreactor... more High strength industrial wastewater was treated using a pilot scale submerged membrane bioreactor (MBR). The MBR was maintained at higher sludge concentration of 14,500 mg/l at prolonged sludge retention time (SRT). It was found that the prolonged SRT MBR could achieve both COD and TOC overall removal efficiencies at more than 99%. The MBR was operated for 300 days without sludge discharge and no deterioration of TOC/COD removal efficiencies being observed. A low specific oxygen utilization rate (SOUR) was found in the prolonged SRT MBR system. This showed that smaller amount energy was required by the microorganisms during the prolonged SRT MBR condition, where maintenance metabolism played the dominant role. Sludge production in the prolonged SRT MBR was consistently low at 0.0016 kgVSS.d !1 with low F/M ratio of 0.11.

Environmental Science & Technology, Mar 19, 2008

An emerging technology for the removal of N-nitrosodimethylamine (NDMA) from drinking and groundw... more An emerging technology for the removal of N-nitrosodimethylamine (NDMA) from drinking and groundwater is reductive destruction using noble metal catalysts and hydrogen gas as a reducing agent. Bimetallic palladium-indium (Pd-In) supported on alumina combines the ability of In to activate NDMA with the hydrogen activating properties of Pd. This study examined the effect of In addition to a commercial 5% Pd by weight on γ-Al 2 O 3 catalyst on the efficacy of NDMA reduction. The pseudo-first-order rate constant increased proportionately to In loading from 0.057 h-1 for 0% In to a maximum of 0.25 h-1 for 1% In and then decreased with additional In loading. Data suggest that hydrogen activation occurred only on Pd surfaces and In activated NDMA 20 times more effectively than Pd on a mass basis. The rate-limiting factor was NDMA activation for In loadings below 1%. The decrease at higher loadings is interpreted as In blocking pore spaces and limiting access to Pd sites, suggesting monatomic hydrogen limitation. The only products detected were dimethylamine and ammonium with carbon and nitrogen balances in excess of 92%, consistent with a mechanism involving reductive N-N bond cleavage. Results from this study serve as a basis for optimizing bimetallic catalysts for treating NDMA contaminated waters.