ABSTRACT
Wastewater treatment systems for individual houses are required to be cheap, robust, compact, hygienic at site and odourless; to have little maintenance; and to be installed and operated by unskilled labour. Their designs are based on full-scale units but are highly modified. Selection depends on (a) the loading to the unit (Table 16.1) (British Water, 2005), (b) the treatment objectives, (c) site conditions and location within the site, (d) effluent discharge requirements, (e) unit requirements (e.g. power, maintenance, etc.) and finally (f) cost. The most commonly employed systems are cesspools, septic tanks, rotating biological contactors (RBCs), constructed wetlands and small complete treatment systems including sand filters. The selection, installation and maintenance of small wastewater treatment systems have been undergoing extensive revision in Europe over the past decade. This has resulted in EN 12566, which is a series of standards entitled Small Wastewater Treatment Systems for up to 50 PT (i.e. population equivalent) published by the Comité Européen de Normalisation (CEN) (Table 16.2). National Codes of Practice within Europe are based on these new standards and codes of practice. Some basic guidelines to the process selection of treatment systems for small communities up to a population equivalent of 50 are given in Figure 16.1.
