Today, great emphasis has been placed on waste produced by the metals industry. Until recently, hydroxide precipitation was considered the ideal choice for handling metallurgical effluents. Metal hydroxides are stored in landfills, although they are not ultimately stable and may redissolve into groundwater with slight changes in pH. / An alternative is to adsorb dissolved metals onto stabilized silica sols ("activated silica"), which are colloidal polymers produced by acidifying silicate solutions. Metal-loaded sol may subsequently be desorbed with concentrated acid. The products are a potentially valuable concentrated metal solution and recyclable sol. / Dissolved metal adsorption with silica sols was compared with precipitation, either with lime or sodium hydroxide. Optimum adsorption and desorption conditions were determined for cobalt. Dissolved metals separation by selective adsorption was demonstrated for cobalt/copper and cobalt/iron (ferric) combinations. A cadmium ion selective electrode was used to examine the adsorption/desorption process "in situ".

A visco-elastic analytical model is presented for the simulation of large scale groundwater flow and land subsidence. Groundwater flow is simulated by a two-dimensional flow model. Land subsidence is modeled vertically by using the Taylor-Merchant one dimensional consolidation theory. In application, multiple aquifers are generalized by using a field approach based on a few 'bulk parameters', which allows the direct use of records obtainable in situ. / The visco-elastic model is applied to analyze and predict the land subsidence in Bangkok, Thailand. The results demonstrate that the visco-elastic model can yield a satisfactory prediction of consolidation that is better than that obtained with the classical Theis-Jacob approach. / Predictions of the piezometric head and subsidence for the 20 years from 1981-2000 were made based on the following three scenarios: (1) a constant withdrawal at 1980's rate, (2) a cessation of all pumping wells, and (3) simultaneous pumping and injection, with injection exceeding 1980's pumping rate by 50%.

The innovative process of removal of toxic heavy metals from water by biosorption, using the dead biomass of Sargassum marine alga packed in flow-through columns, was examined. The mechanism of uptake of Cu 2+, Zn2+, Cd2+, Fe2+, and Cr(III) by the biomass was identified as ion exchange taking place at the weakly acidic functional groups embedded in the cellular matrix of the seaweed. After pretreatment with mineral acids, the cation exchange capacity of the biomass was approximately 2.3 meq/g of biomass dry weight which is comparable to the metal binding capacities of commercial ion exchange resins. / The issues related to the biosorption process design, optimization, and limits of applicability were addressed by (1) evaluating different ionic cycles for biomass in columns at different normalities of the feed, (2) assessing the interference of iron in biosorption of a toxic metal, and (3) analyzing the effects of competitive binding of several toxic metals in the flow-through column including the metal elution order and the overshoots of the concentrations of toxic species in the column effluent over their feed levels. The column models, previously developed for ion exchange, such as the Equilibrium Column Model (ECM) and the Mass Transfer Column Model (MTCM) were used to fit the experimental data and to predict the service time of biosorption columns treating binary and multi-metal mixtures. The application of the theory of ion exchange to describing and assessing the process of metal sequestering by biomass in flow-through columns represents an original work. / The investigation into the removal of hexavalent chromium by Sargassum biomass revealed that the latter could take up approximately 60 mg/g (2.3 meq/g) at pH 2 while reducing some of the Cr(VI) to Cr(III). A combined ion exchange-redox mechanism of Cr(VI) removal was proposed whereby, at pH > 2, the Cr(VI) is assumed to be taken up from water primarily by an anion exchange mechanism, while at pH < 2 the reduction of Cr(VI) to Cr(III) controls the binding of chromium to the seaweed. The effect of pH on the Cr(VI) removal was explained through the dependence of the reduction potential of HCrO4- ions on the pH of the liquid.

The photooxidation of a Thermo-Mechanical (TM) pulp and paper mill effluent with hydrogen peroxide $ rm(H sb2O sb2)$ was investigated at different experimental conditions by using a batch photochemical reactor operating at a dominant UV light wavelength of 253.7 nm. Photolysis of $ rm H sb2O sb2$ produces hydroxyl radicals ($ cdot$OH), which are very powerful oxidizing species. The effluent consisted of a "heat condensate" obtained from toxic vapors generated during various stages of the pulping process. Several operational parameters were varied and their effects on the process were observed and analyzed, in order to achieve its optimization. In addition, heterogeneous photocatalysts such as cupric oxide (CuO) were also investigated as a complement to the photooxidation process. / The main parameter used to determine the quality of the wastewater before and after photooxidation was the Chemical Oxygen Demand (COD), using a closed reflux standard procedure. COD values of the treated solution were determined at subsequent time intervals and used to draw curves illustrating the rate of oxidation of the wastewater. Other parameters, such as Dissolved Organic Carbon (DOC) and dissolved lignin concentration, were investigated towards the end of the research in order to obtain a more complete characterization of the quality of the wastewater after treatment. / The experimental data reveal that there is an optimal $ rm H sb2O sb2$ concentration that is best suited for the photooxidation of the effluent. Moreover, an increase in temperature accelerates the rate of elimination of COD. An increase in effluent concentration is detrimental to the speed of the process, since it causes an increase in its absorbance which can act as a barrier against UV light. The efficiency of the photooxidation process is not affected by variations in the initial pH of the wastewater. Cupric oxide (CuO), when exposed to UV light, efficiently catalyzes the production of OH radicals and is therefore very beneficial to the photooxidation process.

Solubilization of naphthalene and phenanthrene from a synthesized multi-component non-aqueous phase liquids (NAPL) by aqueous in polyethoxylated surfactant solutions at supra-CMC dosages was evaluated in this study. PAHs are abundant at sites contaminated with many chemically complex NAPLs, such as coal tars, creosotes, and petroleum distillates. Surfactant flushing has been proposed to speed remediation at many contaminated sites, due to surfactant's ability to solubilize these hydrophobic compounds. While it is well known that surfactant micelles can solubilize significant amounts of PAHs, this research demonstrates for the first time the relationship between NAPL PAH mole fraction and the solubilization capacity of surfactant solutions. Henry's law satisfactorily described the partitioning of PAHs from hexadecane into water and into surfactant solutions. Selective solubilization of naphthalene over phenanthrene was observed, which is believed to be the result of competition for space in the micelle's outer layers. From these results a predictive relationship between NAPL PAH mole fractions and micellar solubilization is presented.

Rigid spargers are enjoying renewed interest in some flotation column applications such as de-inking of recycled paper and de-oiling of water. Sparger selection depends on the physical characteristics of the porous material, the liquid/slurry properties, and the dimensions of the column. There is no generally accepted method to select spargers for a given flotation column duty. A methodology for selecting stainless steel rigid spargers is proposed. The methodology is based on a target bubble size (db), gas holdup (epsilong), or bubble surface flux ( Sb). It combines two models: one for bubble formation at the sparger proposed by Kumar and Kuloor which relates bubble size to sparger characteristics, and drift flux analysis which relates mean bubble size, gas holdup, and gas rate. / Prediction of bubble size by the Kumar and Kuloor model requires a knowledge of an equivalent pore diameter (De) of the sparger. A procedure to estimate De by fitting the predicted and measured epsilong - Jg relationships is developed. / Comparison of bubble size measured photographically with that estimated from drift flux analysis, and predicted by the Kumar and Kuloor model shows acceptable agreement between the measured, estimated and predicted values. / By combining db predicted with drift flux analysis, and allowing for column dimensions, both the gas holdup and the bubble surface flux were predicted. A maximum in sparger surface area was found above which the gas holdup and the bubble surface flux do not increase. / Spargers were characterized according to their permeability (k ), by applying the Darcy law. Sparger homogeneity was established from this permeability measurement. A relationship between De and k was derived. For spargers with permeability up to 0.75 darcy (0.75 x 10-5 m2), the equivalent pore diameter was constant (De = 2 mum). For larger permeabilities De increased with permeability. / Application of the sparger selection criteria in a pilot unit (0.5 m diameter column) showed epsilong and Sb can be predicted with acceptable accuracy.

Effluents are neutralized with lime forming a voluminous waste sludge which may slowly redissolve in groundwater. This sludge may also be a significant secondary metal source. The present research aims to develop a concept for metals removal and recovery using stabilized colloidal suspensions of activated silica sol, which acts as a neutralizing agent and an adsorption medium. / Silica sol was prepared by firstly acidifying a sodium silicate solution to initiate polymerization, which would ultimately yield a gel. Polymerization was then arrested before gelation by water dilution giving a stabilized, negatively charged sol. Adsorption and precipitation were distinguished by comparing the coloured products from adding silica sol, lime or sodium hydroxide to cobaltous sulphate solution. / Studies of dissolved copper/silica sol interactions showed copper adsorption/desorption to be a reversible pH-controlled process, which was monitored 'in-situ' using a cupric specific ion electrode. Dissolved copper values determined by the electrode were identical to those measured by atomic absorption spectrometry (AAS) for solutions at below pH 7. At above pH 7, the electrode showed zero dissolved cupric, but AAS reported some dissolved copper, attributed to desorbed colloidal cupric hydroxide. A copper/sol underflow sharply divided from a clear overflow were the adsorption products. Addition of concentrated sulphuric acid to centrifuged underflow produced a concentrated copper solution and regenerated sol. The separation of two metals (cupric and ferric) using pH control was also demonstrated. / Adsorption/desorption cycles were used to remove iron from synthetic effluents producing concentrated iron products. Three consecutive cycles were required to produce 30 g/L dissolved iron, suitable for sewage treatment, from 0.5 g/L iron effluent. Final pH control with lime precipitated desorbed colloidal hydroxides. Good settling characteristics following adsorption/precipitation from synthetic and actual mine effluents were observed. Problems included gypsum build-up, while excess silica addition gave dispersion, high silica losses and no phase separation. / Nickel was selectively recovered over iron and magnesium from a tailings pond sludge by acid leaching then solution treatment with activated silica/lime. One adsorption/desorption cycle produced up to a 17 g/L Ni product from 2 g/L Ni leach solution.

The first part of the research deals with the estimation of extreme rainfalls for locations where rainfall records are sufficiently available (gaged sites); the second part is concerned with cases where rainfall data are limited (partially-gaged sites); and finally the third part involves the most complex situation where rainfall data are unavailable (ungaged sites). / For gaged sites, two methods were developed for estimating the annual extreme (AE) rainfalls based on the simple scaling behaviour of the first three non-central moments (NCMs) of the AE rainfall processes and using the Generalized Extreme Value (GEV) distribution as the parent distribution. The first estimation method was called one-moment (OM) method since it only relied on the first-order NCM of AE rainfall series in the computation of the rainfall quantiles, while the second method was called three-moment (TM) procedure since it used all first three NCMs of AE rainfalls in the estimation of the quantiles. / For partially-gaged and ungaged sites, a new approach to defining rainfall homogeneous regions has been proposed based on the similarity of rainfall occurrences at different raingage stations. In addition, a Principal Component Analysis technique was used to assess the similarity of raingages and to delineate homogeneous regions. / On the basis of the proposed method for identifying rainfall homogeneous regions, two new methods (PG-1 and PG-2) were developed for estimating annual maximum (AM) rainfalls at partially gauged sites. These methods were also based on the scaling properties of AM rainfall series for different durations. / For ungaged sites, three methods (UG-1, UG-2, and NR) were proposed for estimating AM rainfalls. Method UG-1 was based on the NCMs of AM rainfalls at an ungaged site that were computed by direct interpolation of the corresponding NCM values from the gaged sites within the same homogeneous region. Method UG-2 used the pooled data set from all gaged sites in the homogeneous region for this computation. On the other hand, the NR method estimated the NCMs of AM rainfalls for an ungaged site using the regional regression between the first three NCMs and the number of rainfall occurrence (NR) values that were interpolated from the NR values of the gaged sites. / Finally, to assess the uncertainty of extreme rainfall estimates, two new methods (CI-1 and CI-2) were developed for computing the confidence limits (CLs) based on these estimated values. The proposed methods were based on the bootstrap technique and the scaling properties of the NCMs of extreme rainfall series.

Batch washing experiments were used to evaluate extractive decontamination of heavy metal polluted illite soils using ethylenediamine-tetraacetic acid (EDTA) and trans 1,2 cyclohexylenedinitrilo-tetraacetic acid (CDTA). Five series of contaminated illite soils were prepared through adsorption tests using four single-specie 5000 ppm heavy metal solutions of Pb, Cu, Zn, or Cd and one multi-species solution containing 1250 ppm of each heavy metal. The five contaminated illite soils that were prepared contained the following levels of heavy metals per kilogram of soil: (i) 5000 mg Pb, (ii) 3490 mg Cu, (iii) 1566 mg Zn, (iv) 700 mg Cd, (v) 1186 mg Pb; 379 mg Cu; 151 mg Zn; and 125 mg Cd. The soil washing results revealed that EDTA and CDTA are equally effective in releasing heavy metals from the contaminated illite soils, with removal efficiencies ranging from 35% to 99% for the 10$ sp{-5}$ M and 10$ sp{-1}$ M solutions, respectively. The optimum pH range for all chelate concentrations and all heavy metal contaminants is between 3-5. Competition between heavy metals in the soil for the adsorption sites of EDTA and CDTA did not have an impact on the removal efficiencies attained. In addition, the heavy metal preferential adsorption sequence demonstrated by the illite soil was $ rm Pb>Cu>Zn>Cd$ for the single-specie pollutant solutions and $ rm Pb>Cu>Zn approx Cd$ for the multi-species heavy metal pollutant solution, and were shown to be mainly bound to the carbonates and Fe and Mg oxides.

The objectives of this study were to look at the effect of kaolinite and cadmium on the biodegradation of naphthalene and substituted naphthalenes. The kaolinite mineral is present in many Quebec soils and is a primary constituent of tropical soils. Since kaolinite is also a well defined mineral, experiments were performed to examine the effect kaolinite might play on the degradation of naphthalene, 2-methyl naphthalene, and 2-naphthol in the presence and absence of cadmium. Furthermore, the results from these analyses were used to interpret the behaviour in the mineralization experiments of each PAH, using the Gram-negative species Pseudomonas putida (ATCC #17484). / The results of this study indicate that the presence of cadmium did not significantly alter the mineralization capacity of P. putida for naphthalene, 2-methyl naphthalene, and 2-naphthol. The presence of kaolinite however, did affect microbial activity by significantly reducing the rates of PAH mineralization. These results illustrate the need to identify the general mechanisms of interactions to develop effective bioremediation programs for contaminated sites. (Abstract shortened by UMI.)