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ASSESSMENT CRITERIA
ACTMAP 2 PART 1: INTRODUCTION
SCOPE
The intention of this ACTMAP is to provide a basis for the evaluation of on-site digesters and their associated pans and squat pans for use with sub-soil percolation systems or small bore drainage systems where conventional waterborne systems are not appropriate as a result of economic constraints, lack of skilled labour, flat topography, etc.
Evaluations based on this ACTMAP facilities decision making on appropriate sanitation methods while ensuring that proven and accepted safety and health standards are maintained as far as the users of the system and the community within which such systems are situated, are concerned.
These criteria are for the assessment of sanitation systems which provide on-site biological decomposition of the sewage in a container producing an effluent which is suitable for disposal on site by means of a sub-soil percolation system (so-called French drain) or for transportation from the site by an effluent collector pipe (also called small bore sewer). Such systems are distinguished from pit latrines in that they produce an effluent in a controlled way, and are distinguished from septic tank installations in that the systems require little water for their operation.
The systems would normally consist of the following components:
- a receiving device or pan
- a discharge duct linking the pan and digester
- a digester tank
- an effluent discharge pipe.
The purpose of these criteria is to provide a basis by which the fitness-for-purpose of on-site digester systems can be evaluated.
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TERMINOLOGY
Pan
A receiving device which may take the form of a squat pan, a pedestal discharging direct into the digester, a purpose-made unit incorporating a tipping tray or a non-conventional pan where less than nine litres of water is used to flush the solids into the discharge duct.
Discharge duct
A means of transporting the waste from the pan to the digester.
Digester
A tank which retains the solids and allows major decomposition of the wastes by natural biological processes.
Effluent discharge pipe
A pipe for transporting the effluent from the digester tank to a sub-soil percolation system, a small bore sewer or conventional sewer system.
A sub-soil percolation system should be designed by a suitably qualified person in accordance with recommendations contained in the National Building Regulations and information sheet BOU 93, or by other authoritative sources.
Conventional waterseal
A conventional waterseal is formed by trapping water in the discharge section of the pan and can take the form of a ‘P’ or ‘S’ trap.
Rough waterseal
A rough waterseal is formed by the discharge duct entering the digester from either the top or the side and projecting a minimum distance below the scum layer (see Figures).
Mechanical waterseal
A mechanical waterseal is incorporated in the pan, providing a barrier (visual and adour) between the digester and toilet superstructure and can take the form of a tipping tray.
Small-bore sewer
Small bore sewer systems are designed to receive the liquid portion of household waste water for off-site treatment and disposal.
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