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Newsletter and Technical Publications
<International Source Book On Environmentally Sound Technologies
for Wastewater and Stormwater Management>

Appendix 2
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)
Bucket Latrine
Pit Latrine
VIP Latrine
Pour-Flush Latrine
Double-Vault Composting Latrine
0.19
0.28
0.55
0.53
0.97
150
5.1
2.6
2.7
0
Aquaprivy
Septic Tank
Seepage Pit
Drain Field
0.53
1.00
1.70
2.50
8.9
8.9
0
0
Conventional Sewerage
Simplified Sewerage
Settled Sewerage
Covered Stormwater Drains
5.29
2.27
1.11
1.38
4.6
16
4.6
16
Communal Septic Tank
Imhoff Tank
Primary Treatment
Waste Stabilisation Ponds
Activated Sludge Treatment
Nightsoil Treatment
0.20
0.41
0.45
0.74
1.80
0.52
10
11
9.3
2.5
6.8
25

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 day.

 

Table 2: Costs per household of three technologies

  Relative Cost US$ (1995)
Pit Latrine 0.28 160
Septic Tank 1 570
Conventional Sewerage 5.3 3020

 

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 maintain.

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.

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