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Wastewater treatment systems abound as a result of technological improvements in treatment processes. Therefore in the selection of a wastewater treatment system for a particular wastewater treatment situation there are many alternatives to choose from. Despite this development municipal wastewater treatment in communities in developing countries are not always sustainable due to the application of inappropriate treatment systems. The question is how can an appropriate treatment system be identified for a certain location? The answer to this question is of importance to developing countries where wastewater treatment is usually not sustainable.
In this study a framework for assessing wastewater treatment systems was developed. First, a comprehensive set of indicators representing parameters of treatment systems and properties of the study area that impacts on wastewater treatment were identified. Secondly, assessment of these indicators were carried out through expert and community survey to identify a final set of indicators whose composition consist of efficiency, reliability and simplicity of treatment systems and resource constraint, resource recovery and environmental concerns of the study area. Thirdly, four wastewater treatment systems, namely: Waste Stabilization Ponds, Trickling Filter, reed bed and free water surface Constructed Wetlands considered to be feasible for the study area were evaluated by the application of the identified indicators. Finally, a decision matrix produced was processed by multi-attribute decision making methods using two indicator weights to identify the most appropriate treatment system among the four alternatives.
Results of the study show that in a scenario where equal indicator weights are assumed, reed bed is identified as the most appropriate with stabilization ponds being ranked as the least appropriate. In a more practical scenario where the weights of the indicators are allocated to reflect conditions of the study area, free water surface is ranked as the most appropriate. This outcome is at variance with stabilization pond technologies currently installed at communities in the study area. The performance of constructed wetlands is at the midpoint as far as most of the high to medium weighted assessment indicators are concern. It therefore represents a compromising solution between waste stabilization pond and trickling filter. The study also shows a change in variants of constructed wetland with a change in indicator weights. An indication that the decision situation determines the appropriateness of a treatment system and not the treatment system itself.
The selection framework employed in this study can be said to be reliable and capable of identifying a treatment system that can be appropriate for a particular location. This is because the choice of a constructed wetland for the study area fits the definition of appropriate treatment system defined by the final indicators identified in this study.