Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>
Costs of Wastewater Management
Cost is an important consideration in the
selection of technology. Decision makers need to know about the relative costs
of technologies, so that a decision to select a particular technology can be
based on sound financial and economic considerations. Cost alone should,
however, not be the sole determining factor in the selection of technology.
Environmental impact of the technologies, such as contamination of groundwater,
should also be considered. Appropriateness of the technology in the context of
the availability of skilled personnel to operate and maintain it, as well as
other social and cultural factors need to be taken into account.
Information on capital cost and the cost
for operation and maintenance for a wide range of technologies is available,
although much of the information is derived from experience in a limited number
of countries. Extrapolation of the data to other locations is fraught with
difficulty. Relative costs may be sufficient to narrow the choice of
technology, although it must be borne in mind that the relative values may
change from location to location dependent of specific local conditions. Cost
of land and of labour in particular can vary considerably. The information
provided here should therefore be used only as a guide of relative costs.
Actual costs for a particular location and community should be ascertained from
suppliers of equipment, materials and labour.
Table 1 indicates the relative costs for
a number of technologies described in the Source Book. The information is
derived from data collected for a computerised decision support system SANEX
(Source Book Section 2 (8.3)). An advantage of computerised decision support
systems, such as SANEX and WAWTTAR, is that the cost information is stored in
the system. Data for a wider range of technology are contained in the systems
than are shown in Table 1.
Table 2 shows actual costs
in US$ for three technologies. These are based on 1995 costs, so inflation from
1995 should be taken into account when calculating costs for any particular
year. It should be noted that these costs are average costs and are based on
information from a limited number of countries.
Table 1: Relative costs of wastewater management technologies
||Capital Cost Ratios
|Annual recurrent cost
(% of capital cost)
Double-Vault Composting Latrine
Covered Stormwater Drains
|Communal Septic Tank
Waste Stabilisation Ponds
Activated Sludge Treatment
Table notes: In
order to peg the ratios, the following assumptions were made:
||The average household consists of five persons.
||One latrine serves one household, so does one aquaprivy. Figures
for these systems include the superstructure.
||The pit emptying interval for latrines is five years.
||Unstable soil conditions require elaborate pit lining even
for simple latrines.
||A septic tank is the conventional type with two compartments,
receiving 200 L black- and greywater per person and day.
||Aquaprivies and septic tanks are desludged every three years.
||The soil absorption capacity is 20 L per square meter
and day. Since authors of most cost figures give no respective information,
this intermediate rate was selected.
||Off-site treatment figures were calculated for a medium size
community of 10,000 persons, with each person discharging 200 L per
Table 2: Costs per household of three technologies
The annual recurrent cost of the technologies is also
indicated in Table 1. It is expressed as a percentage of the capital cost.
Again it should be borne in mind that these are average recurrent to capital
costs ratios. They should be used as guidance only, but they provide a useful
indication of how much a particular technology will require to operate and
Source of costs data: Loetscher, T. (1999): Appropriate Sanitation in Developing
Countries - The Development of a Computerised Decision Aid SANEX. Thesis. Advanced
Wastewater Management Centre, The University of Queensland, Brisbane.