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spent. A better measure is the unit capital cost of a scheme. Communities where the wastes are primarily domestic can be measured in terms of the cost of the scheme per person served. Where there is a significant industrial or commercial load the cost per cubic metre of effluent may be more useful. |
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Operational costs must also be considered. Most sewerage networks operate under gravity and therefore the operational costs are approximately proportional to the size of the network. Schemes including pumping will have higher operational costs and this could be taken into account in the selection process. |
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Most of the factors so far discussed are technical or financial. There will often be other factors relevant to a selection process and peculiar to the particular circumstances. When considering them, it is important that some form of objective measuring and/ or estimation criteria are developed. |
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In many countries tourism is a major source of employment and foreign exchange. The impact on tourists of unsightly polluted drains, bad odours and 'non-standard' sanitary fixtures can far exceed the potential health hazard. This makes many community leaders consider the provision of sewerage a priority in areas where tourism is or could be an important activity. Comparison between communities having a tourist interest is difficult; numbers of tourists, length of polluted drains, length of visible polluted drains or pollution of beaches and bathing waters are all possible criteria. |
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3.2.7
Environmental Impact |
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The impact of a sewerage scheme on the environment may be both positive and negative. Reductions in environmental odour and unsightly pollution within the community may be counterbalanced by increased pollution concentration in the receiving waters with consequent reductions in flora and fauna. Objective evaluation of environmental impact is expensive and requires detailed surveys of the current situation. In this case it is usually sufficient to rely on informed professional judgement. |
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