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This study investigates the existing wastewater management situation in Ethiopia, with particular emphasis on university campus wastewater. The investigation was carried out by reviewing literature, reports, policy documents and field visits integrated with laboratory assessment. It was established that from the seven universities only two have functional wastewater treatment plants, but none of them meet effluent standards. Thesemainly centrally prescribed systemslack sustainability because of problems related to technology choice, affordability and technical skills. This paper proposes feasible rehabilitation strategies for the existing wastewater systems. A combination of policy instruments and integrated wastewater management strategies are proposed. Although based on specific data from Ethiopia, the findings and recommendations of this study also apply to other, similar, low-income countries where the population is booming but overall wastewater management planning is lagging behind. [ABSTRACT FROM PUBLISHER]

In the search for a reliable but simple model for the biodegradation processes of an activated sludge wastewater treatment plant, this paper presents a multi-model which is valid for the global operating region of a standard carbon and nitrogen removing facility. In a first step, locally valid linear models are derived. Two linearization procedures are compared. The first procedure is the classical Taylor series expansion, while the second is a newly developed linearization procedure based on weighted linear combinations. In a second step, the locally valid models are combined to obtain one globally valid multi-model. Previous work has focused on the most basic configuration of one anoxic and one aerated tank followed by a point settler [Smets, I.Y., Haegebaert, J.V. and Carrette, R. and Van Impe, J.F., 2003, Water Research , 37 , 1831 – 1851]. Refinements to the methodology are however needed (and presented here) once the influent flow rate range is increased and the benchmark configuration, proposed by the COST 682 working group no. 2, is taken as the simulation protocol. The main advantage of the obtained linear model (structure) remains the alliance of high predictive power with low complexity, rendering the multi-model fit for on-line optimization and control schemes. [ABSTRACT FROM AUTHOR]

One-dimensional models describing the flow and settling process in secondary settling tanks have great potential with respect to process control. Most of these models are based on a conservation equation that is discretized by dividing the settler into a fixed number of horizontal layers. In this article, the focus is on convection-diffusion models, which - in contrast to other one-dimensional models - ensure mesh-independent concentration profiles. The sensitivity of a prototype convection-diffusion model with respect to its parameters and the loading and operational conditions is studied by means of steady-state simulations. Based on the results, the importance of each of the model parameters is assessed. For each combination of parameter values, loading conditions, and operational variables considered in the study, the minimum number of layers required to obtain a practically mesh-independent concentration profile is determined on the basis of a newly developed objective criterion. This analysis leads to the identification of those factors having a large influence on the numerical behavior of the model. [ABSTRACT FROM AUTHOR]