Increasing attention has been given to the role of colloids in accelerating contaminant transport as evidence of significant subsurface transport of contaminants continues to be presented. Colloid migration models typically include the processes of advection, dispersion, deposition and release. Present models are limited in their ability to predict the transport and fate of colloids due to limited understanding of the interaction between these processes. The objective of this research is to gain a better understanding of the physical/chemical factors which affect the transport of colloidal particles. Laboratory-scale experiments were conducted in two phases to examine the effects of different chemical and physical factors on colloid transport. In the first phase, pulses of 1.09 and 0.28 $\mu$m fluorescent particles were injected into sand-packed columns under constant chemical conditions, and the response monitored over time. The second phase consisted of making a step change in solution chemistry (reduction in ionic strength or increase in pH) or flowrate to the system and monitoring the fluorescence response over time. The relative impact of various processes including advection, deposition/release, retardation and hydrodynamic chromatography on colloidal transport was evaluated using experimental results. Various mathematical models were evaluated for their effectiveness in describing the observed colloid migration. Results of finite pulse experiments conducted under constant chemical conditions confirm that solution chemistry is a key factor affecting particle deposition and release. Deposition results show evidence of the effects of hydrodynamic chromatography and retardation. As expected, deposition increases with increasing ionic strength. Perturbations in solution chemistry caused the subsequent release of particles. However, the amount released was only a fraction of the total deposit. The release process warrants further research.

Chemical characteristics and environmental behavior of halogenated organic (OX) compounds in biologically treated wastewater from a secondary-fiber mill were investigated. Liquid-liquid extraction techniques were developed and optimized for the identification and quantification of OX compounds from this sample matrix. Twenty OX compounds were identified in the treated wastewaters, accounting for 20 to 60 percent of the total organic halide in the wastewater. A significant fraction of the OX in the treated wastewater was accounted for by one single compound: 1,3-dichloro-2-propanol, which persisted through biological treatment. Much of the the organic matter in the wastewater. Volatilization was identified as a prominent transport process that affected the fate of a small fraction of the identified OX compounds. Photolysis was the only environmental transformation process that could effectively reduce trichlorophenol concentrations within the time-scales studied at this site. A significant portion of the OX was relatively stable under typical environmental conditions, resulting in its persistence in the receiving water body. Conventional biological treatment was not effective in reducing OX concentrations in the wastewater. Advanced processes like chemically assisted secondary clarification (with alum and ferric chloride) and dechlorination (with sulfite) did not have a significant effect on OX removal. Ozone oxidation and alkaline hydrolysis reduced OX concentrations in the effluent by over 50 percent.

This study investigates the removal of natural organic matter (NOM) by alum coagulation, and the effect of ozonation on this process. The objectives of the research were: (1) to determine various properties of NOM that are important for its interaction with alum, and the effect of ozone on these properties, (2) to determine the calcium and aluminum binding capacities of unozonated and ozonated NOM, (3) to determine the sorption capacity of unozonated and ozonated NOM on aluminum hydroxide flocs, and (4) to use the data thus obtained to describe NOM removal by alum coagulation, and the effect of ozonation on this process. For the purpose of this research, NOM from a eutrophic raw water source (Forge Pond, Granby, MA) was isolated and fractionated into eight fractions based on relative hydrophobicity and acidity. The fractions isolated were: fulvic acid (FA), humic acid (HA), weak hydrophobic acids (WHYA), hydrophilic acids (HAA), hydrophobic bases (HYB), hydrophilic bases (HYB), hydrophobic neutrals (HYN), and hydrophilic neutrals (HN). The objectives of the research were met with a series of carefully controlled experiments conducted with raw water and the above fractions. It was postulated that the interactions between charged functional groups on NOM molecules and coagulants was responsible for the removal of NOM by alum coagulation. Two mechanisms for such removal are charge neutralization/precipitation and adsorption of NOM on aluminum hydroxide flocs. The acidic NOM fractions (FA, HA, WHYA and HAA) were negatively charged at all pH values, and hence interacted well with the positively charged aluminum hydroxide particles. Of all the NOM fractions isolated, the humic fractions (FA and HA) exhibited best adsorption on aluminum hydroxide flocs. The basic and neutral fractions (HB, HYB, HN and HYN) had little or no charge, and hence exhibited poorer adsorption than the acidic fractions. Calcium and aluminum complexation studies showed that the negative charge on most acidic fractions were only partially neutralized due to metal complexation. The charge on the basic and neutral fractions, on the other hand, were completely neutralized by metal complexation. Thus it was concluded that the charge neutralization/precipitation mechanism of NOM removal was only important for the basic and neutral fractions. Ozonation increased the charge of all NOM fractions. The adsorption of the acidic fractions on aluminum hydroxide flocs either remained unchanged or decreased upon ozonation. Hydrophilic neutrals (HN) on the other hand showed increased adsorption on aluminum hydroxide flocs on ozonation. It was also shown that in the case of Forge Pond water, increased NOM removal on ozonation may only be obtained if ozone is allowed to react with the non humic components of the NOM exclusively.