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.

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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.

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