A comparison of sewer reticulation system design standards gravity, vacuum and small bore sewers

The introduction of waterborne sewerage in the villages and towns of Botswana has highlighted a number of problems in the design of the reticulation systems. The first of these is that not many people connect to the system once it is installed. The second problem is that there are not always the skills required to maintain the systems in the rural areas. Thirdly Botswana being a dry country does not always have the water supply available and only some households have a house connection which provides enough water to flush a gravity sewer. Coupled to this is the low housing density and generally flat landscape in rural Botswana that means the conventional gravity sewer soon requires deep excavations and the consequent need for pumping stations. It became apparent that gravity sewer systems were not always the best means of providing waterborne facilities. It was found that in certain circumstances the alternative options of vacuum and small-bore sewers were more appropriate and so design standards were developed for gravity, vacuum and small-bore sewer systems. This allows for a uniform approach to design in order to achieve a functioning system. Water SA Vol. 30 (5) 2005: pp.137-144