The integration of offshore wind farms through Multi Terminal DC (MTDC) networks into the GB network was investigated. The ability of Voltage Source Converter (VSC) High Voltage Direct Current (HVDC) to damp Subsynchronous Resonance (SSR) and ride through onshore AC faults was studied. Due to increased levels of wind generation in Scotland, substantial onshore and offshore reinforcements to the GB transmission network are proposed. Possible inland reinforcements include the use of series compensation through fixed capacitors. This potentially can lead to SSR. Offshore reinforcements are proposed by two HVDC links. In addition to its primary functions of bulk power transmission, a HVDC link can be used to provide damping against SSR, and this function has been modelled. Simulation studies have been carried out in PSCAD. In addition, a real-time hardware-in-the-loop HVDC test rig has been used to implement and validate the proposed damping scheme on an experimental platform. When faults occur within AC onshore networks, offshore MTDC networks are vulnerable to DC overvoltages, potentially damaging the DC plant and cables. Power reduction and power dissipation control systems were investigated to ride through onshore AC faults. These methods do not require dedicated fast communication systems. Simulations and laboratory experiments are carried out to evaluate the control systems, with the results from the two platforms compared.

The problem of domestic solid wastes buried in landfill sites is viewed from the aspect of leachate contamination and migration in the substrate. Generally, this occurs through the penetration of the contaminant into the liner material. This study assesses the efficiency of natural clay barriers as an expedient economic lining material. / Various chemical constituents of the landfill leachate of an actual waste containment site at Lachenaie (35 km east of Montreal) were determined from samples collected from specially designed basins. / In companion laboratory tests, these leachate samples were permeated through laboratory columns that contained the natural clay compacted at the optimum water content. The columns were constructed so as to permit simulation of slow, saturated, anaerobic flow of leachate through the clay lining surrounding the landfill and leachate basins. Leachates were permeated through the soil columns for periods of four to five months, during which effluents were collected periodically and analyzed for different chemical species and physical parameters. These chemical analyses measured changes in the concentration of: (a) cations (Na, K, Ca, and Mg), (b) anions (Cl, HCO$ sb3$, and CO$ sb3$), (c) total organic carbon (TOC), and (d) heavy metals (Fe, Zn, Pb, and Cu). The physical parameters measured included: (a) pH, and (b) specific conductivity. / Subsequent to the leaching tests, the column contents were cut into six sections and analyzed to determine the distribution profiles of the adsorbed and retained contaminants at various time durations. / Predictions, using a dispersion-convection model for concentration profile development for either adsorbed or retained contaminants, were compared with the experimentally determined profiles (both in leaching columns and landfill laboratory model). / Another set of experiments was also conducted to evaluate the effect of some organic fluids on the geotechnical properties of different clay soils (natural clay and two reference clay soils: illite and kaolinite). / The results from this study have demonstrated that the natural clay soil can be used to adequately contain the different contaminant species usually present in the leachate solutions. Furthermore, the data suggested that under favourable soil conditions, landfill leachates containing low levels of trace metals will not pose a substantial contamination threat to the subsurface environment, provided that a proper thickness of barrier is used. (Abstract shortened with permission of author.)

Ten dry cleaning sites were evaluated in the Houston area. At the dry cleaning sites studied, the contamination may be attributed to deficiencies in the separation equipment of the dry cleaning equipment, allowing free phase perchloroethene (PCE) to enter the sanitary sewer lines and escape by permeating through the pipe, or through defects in the pipe. Three sites with different geologic characteristics were chosen for intensive study to examine if there exists a pattern of transformation of PCE to the daughter product trichloroethene (TCE) in the sites. Transformation is compared by calculating the ratio of PCE to TCE for each well for a single sampling event, and by modeling at one of the sites. One site was modeled with the model RT3D, and the results from the model confirm the change in PCE to TCE ratio as being a result of a change in the reaction rate. A pattern was noticed in the site data which sites with sandier hydrologies, as measured by hydraulic conductivity, tended to have lower transformation rates than sites with tighter formations. It is suggested that this difference in apparent reaction rate may be due to enhanced reaction in the tighter formations due to lack of oxygen recharge, leading to an anaerobic region that is conducive to reductive dechlorination.

Fluid mechanics of a channel with one porous wall was studied from first principles as the initial step towards understanding polarization phenomena in membrane modules. A regular perturbation method was used to solve the steady-state Navier-Stokes equations for an incompressible, constant property fluid in two dimensions with uniform suction and slip at the permeable boundary. The effects of solute and hydrodynamic parameters on concentration polarization during potable water treatment applications are investigated numerically. Inertia dominated and permeation drag dominated particle transport is discussed. Experimentally determined residence time distributions of particles in a microporous channel are interpreted in the light of inertial and permeation forces. Inertial lift theory is shown to predict initial particle transport. Experimentally observed long trailing edges in particle residence time distributions indicate the importance of other transport mechanisms even in dilute suspension mechanics. It is seen that inertial effects are negligible under conditions typical of microfiltration.

Diurnal variations of flow rate and organic load cause difficulties in the operation of wastewater treatment plants. The man-made hydraulic shocks produced by the installation of fixed speed pumps upstream of the treatment processes further amplify the frequency and magnitude of these variations. The major objective of this study is to develop control strategies to minimize these variations. A dynamic model has been developed for the operation of fixed speed pumping stations. The optimum control strategy based on this model can reduce the on-off pump cycles up to 86% for a typical day as compared with ordinary two point control. Optimum models and corresponding control algorithms have also been developed for the operation of in-line equalization basins. These models have shown potential for the reduction of the required equalization volume and can provide smoother outflow to the downstream processes. A reduction of tank volume by 63.5% has been obtained in the simulation using the optimum control strategy.

A database for surface impoundments (SIs) consisting of hydrogeologic and operational parameters was developed and statistically analyzed. The database was used to evaluate infiltration, groundwater mounding, contaminant transport (dilution), and the relationships between each of these mechanisms. Analytical, numerical, and statistical solutions were used for the evaluation. Hydraulic heads calculated with Hantush's analytical solution for mound growth compared well to those computed by a two-dimensional numerical transport model for unconfined aquifers (UNMOC). Infiltration from the "typical" surface impoundment (defined by the database) was modeled with UNMOC. Dilution effects were quantified and compared to those predicted by the one-dimensional Monte Carlo model (EPACML) used by EPA in specifying acceptable waste concentrations for disposal. The SI-specific database in conjunction with UNMOC predicted much less dilution than EPACML and provide an alternative approach to regulating surface impoundments.

Much attention has been devoted to the design and construction of wastewater treatment plants. However, relatively little attention has been devoted to plant operations. Knowledge based or expert systems are oriented toward improving operational procedures and thus have significant potential for solving control problems. This paper presents the results of a study conducted to examine the use of expert systems technology for computer assisted operation of the anaerobic digestion process. Knowledge was divided into mechanistic understanding of the process and that which comes from experience (heuristic). Effective operation requires both types of knowledge. A process task analysis identified four major tasks. These are monitoring, state assessment, control decision and execution tasks. The analysis suggested an expert system configuration consisting of software modules corresponding to these tasks. Development of the state assessment and control action modules was stressed. The capture of mechanistic knowledge was emphasized. Knowledge was represented using if-then rules. Diagnostic rule development was accomplished using computer simulations of hydraulic, organic, toxic and ammonia upsets which could cause process failure. Rules relating to control included decision rules which specified appropriate control actions and fuzzy rules which specified the amount of control. Additional simulations of process upsets were used to examine the behavior of the system. Several different upset states were properly identified and corrected by the system. The control actions used were influent flow control, dilution, organism recycle and acid or base addition. The rule-based approach was found to be flexible and transparent. Theoretical knowledge from the mechanistic model could be converted into a language understood by operations personnel. However, the expressive capabilities of the rule language and the inability to ensure consistency and completeness in the rule base limited the system. An expert system is knowledge intensive and knowledge transfer from the expert to the computer and from the computer to the operator are important factors. Field testing will be needed to validate the rules developed for the expert system. Future research should emphasize the development of a body of knowledge about process operation. Alternative knowledge representations and hybrid systems integrating expert, fuzzy and stochastic control techniques should be studied. In combination these provide powerful tools for solving the problems of control in wastewater treatment.

A model is developed that calculates capital and operating cost of cross-flow membrane filtration as a function of relevant design parameters. An expression for capital cost is empirically derived from information gathered from membrane manufacturers. Operating cost is divided into components for energy consumption, chemical demand, membrane replacement and concentrate disposal and is determined from attributes of the membrane system. The effect of operating parameters and membrane characteristics on cost are examined. The flux of permeate across a membrane is the principle factor determining cost. Energy cost, although important to the daily operating cost of a water treatment plant, is overshadowed by the membrane replacement cost. The effect of backflushing procedures on cost is evaluated using empirical functions for permeate flux derived from a microfiltration pilot study. Microfiltration is determined to be a cost-competitive alternative to ultrafiltration. Costs calculated by this study are compared to reported costs for membrane filtration.

Recent evidence indicates that ferrous carbonate (FeCO$\sb3$, siderite) plays a critical role in forming corrosion resistant scale. Although FeCO$\sb3$ also limits the solubility of iron in some anaerobic systems, its precipitation kinetics have received little attention. The temperature dependent precipitation kinetics of ferrous carbonate were studied using a powerful new "temperature ramped" approach. Activation energies calculated using three second order and two first order precipitation models (53.8-123 kJ/mol) all qualitatively indicate that precipitation is controlled by surface reaction rate. Precipitation is extremely slow at ambient temperatures, but becomes limited by diffusion above approximately 110 C. Surface reaction rate equations must, therefore, be used to model low temperature precipitation, and mass transfer equations should be used to estimate high temperature FeCO$\sb3$ growth. Seed crystals were prepared and Ostwald ripened in a reactor under anoxic conditions. Precipitation was induced by linearly increasing (ramping) the temperature and recording the change in iron concentration with respect to time and temperature. Rather than performing a series of isothermal experiments, temperature dependent kinetics were determined by fitting nonlinear models to temperature ramped experiments. The techniques developed in this research could easily be adapted for use with a number of other reduced metal systems.

Leather tanning, one of mankind's oldest industries, is in a time of environmental transition. Traditionally a "wet" industry, many processes result in pollution loads which are not acceptable in today's legislative environment. For this study, the largest Canadian Retanner, located outside of Montreal, Quebec, allowed its processes and associated waste products and loads to be characterized. A physico-chemical treatment regime, utilizing precipitation, coagulation, and flocculation technology, was then proposed and implemented on the laboratory level. The results were positive, but the solid waste product from treatment was found to present its own set of environmental problems. Finally, the various reuse, recycling, and reduction opportunities applicable to the tanning industry were explored, as was their applicability to the re-tanner in question.