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Financing water infrastructure has been increasingly identified as a constraint to reaching the Millennium Development Goals for developing countries' water sectors and a significant area in which potential exists to develop sustainable financing is through the design of appropriate tariff policies. / This thesis examines in detail the demand for water service improvements by analysing the willingness to pay for such improvements in Trinidad and Tobago. The basis for the work is a household sample survey conducted in 2003 which assessed the current quality of service and attitudes towards changing the status quo situation. The survey of 1419 households showed that services are poorer than officially stated, and that in response many households have opted for private coping solutions to mitigate the poor service levels of the utility. / Choice experiments, which have only limited previous application in the sector, are employed to develop attribute based utility models describing the welfare effects of service level changes, in addition to the more commonly used contingent valuation method. A rigorous comparison of the two methods is developed. It provides evidence that the choice experiment methodology has benefits for policy analysis around the willingness to pay for service changes in the water sector. / An analysis of proposed marginal cost based tariffs in Trinidad, as a part of wider sector reforms, is used as a case study for the policy applications of the choice experiment based willingness to pay data. Consumers are willing to pay for investments in water infrastructure, provided that they impact upon the actual service received. Marginal cost based tariffs might be socially unacceptable given that whilst significant, the willingness to pay, given likely service changes associated with planned investments by the Trinidadian water utility, for service changes is not sufficient to cover this economically efficient level of tariff.

Anaerobic packed bed processes are used to treat industrial wastes containing high concentrations of readily biodegradable organics. Dynamic mathematical models for anaerobic up-flow and down-flow packed bed processes have been developed and verified semi-quantitatively by using experimental data and information from the literature. The dynamic models are then used to study the dynamics, stability and control of the process. The biological kinetic models involve four different groups of bacteria: acid producing bacteria (X$\sb{\rm G}$), hydrogen utilizing methanogens (X$\sb{\rm H}$), acetoclastic methanogens (X$\sb{\rm A}$) and propionic acid utilizing acetogens (X$\sb{\rm P}$). The effect of hydrogen on the acid formation stage and propionic acid degradation has been incorporated in the models using complementary Monod type equations. Modified inhibition functions are proposed for the growth rates of X$\sb{\rm A}$ and X$\sb{\rm P}$. In these functions, high concentrations of total unionized volatile fatty acids and unionized propionic acid are assumed to be toxic to X$\sb{\rm A}$ and X$\sb{\rm P}$, respectively. The hydraulic model of the up-flow anaerobic packed bed process is represented by a slurry reactor followed by a fixed film reactor approximated by complete mixing tanks in series. A constant thickness of biofilm and uniform bioactivity are assumed for the down-flow anaerobic packed bed process. A single complete mixing tank with dead space, short circuiting, and complete mixing tanks in series is used for approximating the hydraulics of down-flow process with and without recirculation, respectively. Semi-quantitative agreement between simulation results using the proposed models and data obtained from experiments and the literature was obtained. High resistance to hydraulic overloading and rapid recovery after shock loadings was demonstrated for the anaerobic packed bed processes. The model suggests that the more intense the overload, the greater the accumulation of propionic acid. System failure due to organic loadings could be predicted by incorporating modified inhibition functions into the overall model. The concentrations of hydrogen and propionic acid can be good stability indicators. On-off control of the recycle flow rate using hydrogen and propionic acid concentrations as the measured variable was simulated. This control strategy can prevent process failure for pulses of short duration and delay process failure for step changes. The time delay obtained by this control can provide operators the time needed to take other corrective actions.

Retention of atrazine from simulated surface water was measured using dialysis membranes with molecular weight cut-offs similar to those of pressure-driven ultrafiltration and nanofiltration membranes. Atrazine was significantly retained by membranes in the nanofiltration range in the presence of organic matter (OM), presumably by association with OM. Atrazine rejection was independent of initial concentration. Increasing OM concentration increased atrazine retention. Solution chemistry was important in determining the extent of atrazine retention. Where OM aggregation increased, atrazine rejection decreased, and visa versa. Increasing salt concentration decreased atrazine rejection. This effect was stronger with calcium than with sodium and protons. It is speculated that the most likely mechanism of atrazine retention with OM is through its diffusion into the interior of the organic matrix and subsequent physical trapping. This implies that atrazine rejection in surface waters will increase with increased OM concentration and decreased hardness in the influent surface waters.

The purpose of this study was to develop a technique for on-line estimation of oxygen uptake rate (OUR) and to investigate the use of OUR in monitoring and control of the activated sludge process. A mathematical expression for the relationship between the plant specific oxygen transfer coefficient (K) and air flow rate was necessary for the estimation of OUR. Three different least squares methods, a direct linear method, a discrete linear method, and a non-linear method, were investigated as estimation techniques for K. Data from a full-scale, instrumented wastewater treatment plant were collected in order to evaluate the usefulness of each of the three methods. It was found that the direct linear method with data smoothing, although mathematically less rigorous than the other two methods, yielded a satisfactory estimate and was preferred over the non-linear method because of its computational simplicity. Difficulties were encountered with the discrete linear method because of disturbances in flow rate at the plant due to the on-off operation of several influent pumps. A comparison between the measured and estimated OUR showed similar trends indicating that the estimated OUR could be used in control. The use of OUR for control purposes was investigated by means of computer simulations using an existing mathematical model modified to simulate conditions at the full-scale plant. Control strategies, using OUR estimates, for air flow rate and step feed manipulation were developed and demonstrated to be effective. Because OUR is a better indicator of sludge activity than dissolved oxygen, the estimated OUR may also be used to monitor process conditions and obtain an estimate of the active fraction in the sludge. The latter may enable improved control strategies for sludge age to be developed.

The purpose of this investigation was to develop and validate at full-scale dynamic models and control strategies for the activated sludge process capable of predicting both the clarification and thickening functions of the solids-liquid separator. This also included the development of a hydraulic model capable of predicting flow transients through the treatment plant and a solids model to predict MLSS concentrations in the reactors for arbitrary hydraulic forcings. These models were then utilized to derive control strategies to minimize the discharge of effluent suspended solids. A mixing model was identified using tracer tests. Analysis of the data demonstrates that a tanks-in-series model describes the reactor system better than a dispersion model. A hydraulic model was developed from mass balances and well known flow equations. The model demonstrates the limited dampening capacity of treatment plants for hydraulic disturbances. Full scale experiments to identify models and estimate parameters were performed at a 5 MGD wastewater treatment facility in Houston, Texas. A distributed computer monitoring and control system consisting of on-line instruments, programmable controllers, and a minicomputer were installed at the plant. A table-driven data acquisition and control software package was implemented. Numerous experiments demonstrated that influent flow rate and pattern were the most important factors affecting the effluent suspended solids concentration at the plant studied. Hydraulic transients had an immediate effect which persisted longer than the actual disturbance. The recycle flow rate had relatively small effects. The sludge blanket level also had little effect until it was very near the water surface. A model was proposed which incorporates these features. A sludge thickening model developed by Stenstrom was modified to account for the conical bottom of the settler. The model is capable of predicting the return sludge concentration and the accumulation of solids in the settler. Settling parameters were estimated from batch settling tests in a stirred vessel. These models were utilized to derive an influent pumping strategy to minimize the discharge of effluent suspended solids. The strategy employs flow forecasting and a Simplex optimization routine to utilize the dampening capacity of the wet well in an optimal manner. A recursive state/parameter estimation technique was adapted for use with the clarification and thickening models. This technique can be used to give better estimates of the model states and update the model parameters from on-line measurements.

Field monitoring at the United Creosoting Company (UCC) site in Conroe, TX has shown that the shallow aquifer has become contaminated by leakage from two unlined ponds. A plume of hydrocarbon contaminated ground water is present and is contained within a large plume of elevated chloride concentrations. This difference in size could be due to two processes: adsorption and biodegradation. A series of field tests and computer simulations were performed to identify which processes were limiting the transport of the hydrocarbon. A seven day injection-production test was performed in the shallow semi-confined aquifer at the site and clearly demonstrated that adsorption was not significant in retarding the movement of naphthalene. Loss of naphthalene and paradichlorobenzene during the test suggested that biotransformation of the hydrocarbon could be significant. Previous laboratory studies (Lee and Ward, 1984) had shown the potential for rapid biotransformation of the hydrocarbon when oxygen was added but very minimal transformation in the absence of oxygen. In the shallow aquifer at the UCC site, oxygen is present at low concentrations and could potentially result in limited biotransformation of the hydrocarbon plume. In order to study this phenomenon, a series of numerical models were developed to simulate the transport of oxygen and hydrocarbon in ground water and resulting biodegradation. Numerical simulations generated with these models suggested that in most ground water environments, microbial kinetics will be rapid relative to mass transport and biodegradation will be limited by the rate of mixing between oxygen and hydrocarbon. The numerical models were then tested by comparing numerical simulations to field data collected at the UCC site and the results of a series of single well push-pull tests designed to measure in situ biotransformation. Finally, the calibrated model was used to compare various alternatives for restoration of the UCC site.

The objective of this study was to develop an integrated control strategy for the activated sludge process. For the purpose of this study, the system included the influent pump station, the biological reactor, the air supply and distribution system, and the solids-liquid separator. A comprehensive dynamic model was developed for the system and control was superimposed on the model. The overall model of the system consisted of deterministic and stochastic components. The models for individual process units were taken from the literature and modified where necessary to include features necessary for control strategy development. Computer simulations were used to investigate the control strategies, interactions between the control loops, interactions between process units, and between design and operation. A limited amount of data was available from a full scale experiment conducted at a wastewater treatment plant in Houston, Texas. The objective function was to minimize operating costs and permit limits were treated as constraints. The control strategy for the biological reactor was based on a definition of process state consisting of a combination of D.O. concentration and specific oxygen uptake rate. A rule based controller was designed to maintain the optimal process state. Computer simulations suggested that control of flow between the biological reactor and the separator was capable of eliminating high frequency variations in flow rate. This strategy was proposed for minimizing adverse effects on clarification. For low-friction-head, high-static-head pump stations, on/off pumping was found to require less energy than variable speed pumping or automatic throttling of the discharge. Due to the small size of the wet well, variable speed pumping was found to be incapable of significantly dampening variations in influent flow rate.

Of the wastewater treatment plants (WTPs) in the province of Quebec that are effecting a phosphorus (P) removal program, chemical addition and precipitation is the primary form of P-removal, with biograss growth and/or enhanced biological P-removal (EBPR) providing secondary removals. An overall P-removal of approximately 66% was achieved at these WTPs in 1994. / Dessau Inc. of Laval, McGill University and Ecole Polytechnique were contracted by the Ministry of the Environment and Fauna of Quebec to perform an evaluation of chemical P-removal from Quebec municipal wastewaters and the optimization of existing processes. Part of this evaluation and optimization involved clarifying the mechanisms and interactions during chemical P-removal. Many key models from literature were reviewed, but were not entirely adequate. / A static steady-state P-removal model was therefore developed, accounting for the reactions and removals of soluble and particulate forms of orthophosphate and polyphosphate/organic phosphorus. The model traces the path of each P-fraction throughout the chemical removal process, accounting for P-precipitation and adsorption, as well as reductions of TSS and BOD$ sb5.$ Computer programs were constructed for the model, with specific programs written for primary treatment, activated sludge, biofiltration and facultative aerated lagoons. / Samples were gathered at 11 WTPs during June-July 1994; these field data were used to calibrate the computer programs. Computer program output generally agreed with the field data to within 10%. Several of the WTPs sampled obtained a total-P removal of approximately 90% with metal dosed:P molar ratios often below 1.

The efficiency of UV disinfection of wastewater is limited by particles that shield embedded pathogens. The objective of the experimental work presented herein was to investigate if the addition of microorganism-free, inert, solid, incinerator ashes would create more readily disinfectable particles by concentrating pathogens at the surface of particles. The ensuing reduction of embedded pathogens would increase the efficiency of UV disinfection. / Wastewater from the Montreal Urban Community wastewater treatment plant (MUCWTP) was used for the study. The wastewater contained domestic and industrial influents, as well as urban runoff. The physicochemical treatment of the MUCWTP was simulated using a modified jar test. Ash particles (200 mg/L; <75 mum) were added at the same time as either the addition of the coagulant or the coagulant-aid. Furthermore, some tests were done by coating ash particles with a coagulant or coagulant-aid. UV disinfection was carried out on the jar test supernatant at doses of 25, 32, and 40 mW.s.cm-2. / Results showed that the addition of ash particles improved the efficiency of UV disinfection by as much as one log reduction, but the improvement was not statistically significant at the 0.05 level when tested with the one-way ANOVA parametric test and the Friedman non-parametric test. / An analysis of the mechanisms of agglomeration with and without the addition of ash indicated that the efficiency of the UV disinfection process appeared to be enhanced through the production of numerous small flocs, which, however, lowered the overall quality of the physicochemically-treated effluent.