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simplified sewerage? If the community already has septic tanks, then (assuming the soil can no longer accept the septic tank effluentbut see below) probably settled sewerage will be cheaper than simplified sewerage; but, of course, this needs to be checked in each case. |
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However, if the reason why the soil can no longer accept septic tank effluent is simply because of a high, in-house water consumption (>100 litres/caput day), with a correspondingly high wastewater generation, then serious consideration should be given to in-house water conservation techniques, such as the installation of water-saving plumbing fixtures (see Mara, 1989), in order to reduce the resulting wastewater flow such that the soil is again able to accept the septic tank effluent. |
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2.2.4
The Case for Simplified Sewerage |
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As will be now apparent, there is a general case in low-cost urban sanitation programmes and projects, especially those in high-density settlements, for considering simplified sewerage as the sanitation technology of first choice. It needs to be confirmed, therefore, in each situation whether simplified sewerage is: |
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cheaper than on-site sanitation, and |
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cheaper than settled sewerage |
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Simplified sewerage would, therefore, only not be finally selected if it were in fact not cheaper than either of these alternatives. This is only likely at low-population densities or in areas already served by septic tanks (even currently malfunctioning septic tanks). |
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A final decision to make concerning simplified sewerage is whether to adopt condominial (or backyard) sewerage or in-street sewerage. The former is more generally favoured in northeast Brazil, for example, and the latter in southern Brazil where SANEPAR, the water and sewerage company of the State of Paraná, often installs 'double sewers', i.e. a sewer on each side of the street under each sidewalk. It is not clear whether the reasons for this are always really valid, but what is clear is that 'double in-street simplified sewerage' is significantly (about two-thirds) more expensive than condominial sewerage (Hamer, 1995; Mara, 1996). |
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