estimating the financial costs of sanitation systems

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Estimating the financial costs of sanitation systemsEstimating the financial costs of sanitation systems

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Loetscher, Thomas, and Jurg Keller. 2019. “Estimating the Financial Costs of Sanitation Systems”. figshare.https://hdl.handle.net/2134/29270.

https://lboro.figshare.com/

A SANITATION: LOETSCHER and KELLER

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Thomas Loetscher and Jürg Keller, Australia

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ANYONE WHO EVER tried to find information on thecost of sanitation systems, particularly on on-site facilities,knows how scarce and scattered these data are, and howdifficult their interpretation is. In the course of his work, theauthors found that on the other hand there is a widespreadinterest in information that allows at least an approximateestimate of the costs incurred by sanitation projects. Thispaper discusses the development of around 50 costingfunctions for a wide variety of alternatives ranging fromsimple pit latrines to sewerage and centralised treatmentworks such as the activated sludge process. Basically, thesefunctions were established using relative cost estimatesfrom a variety of sources and cost-capacity relationships.They allow estimates of the capital and the recurrent costsof sanitation alternatives. Not surprisingly, the reader willfind that many assumptions underlie this work. It is recog-nised that while most of them are underpinned by evidencefrom literature or other sources, some might be question-able. It is thus hoped that this contribution will receivescrutiny from its readers and stimulate discussion.

��The work presented in this paper was carried out for thedevelopment of the expert system SANEX© for the evalu-ation of sanitation alternatives in developing countries.SANEX© uses around 50 technical, sociocultural andfinancial criteria in order to assess more than 80 sanitationsystems, ranging from simple latrines to sewerage, with

respect to the indicators ‘Implementability’ and‘Sustainability’.

One of the software’s main features is its capability toestimate the costs of these systems based on costing func-tions. These functions can be expected to yield estimateswith an order-of-magnitude accuracy, which, by defini-tion, is within +/- 30 per cent of the actual costs (Bauman,1964). Although the validity of absolute estimates mightsometimes be questionable, the relative cost ranking ofalternatives is usually of good accuracy. The results gener-ated by the functions represent financial costs, indicatingwhether beneficiaries can afford certain sanitation systems.They do not tell us about their economic merits. A moredetailed comparison of financial versus economic costs isprovided in a technical note from WASH (1992).

�� All costing equations yield estimates for the United States,from where the most abundant and reliable absolute costinformation was available. However, the author developeda simple method for converting the US figures to accountfor regional construction costs in any project locale. Thepublication of this method, which is based on the localresidential building cost and which was implemented inSANEX©, is planned.

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Since factors such as the locality, base year and exchangerates only influence relative costs to a limited extent,relative figures from various sources and locations can bedirectly compared. Thus, in a first step, information on therelative cost of sanitation systems was collected mostlyfrom literature (e.g. Kalbermatten et al., 1982). Subse-quently, fixed (default) community conditions (10,000persons, 5 persons per household, etc.) were used toestablish the capital costs of all sanitation technologiesrelative to the two-compartment septic tank, the cost ofwhich was assumed to be 100 per cent (= 1). These relativefigures were pegged to the absolute cost of a septic tank indefault conditions, which, based on various sources, wasdetermined to be $570 (1995). Table 1 shows an excerptfrom the results.

A = Land cost, US$/m2

Cc= Capital cost, US$ (1995).Cr= Recurrent cost, US$ (1995).D = Population density, persons/ha.Fe = Frequency of pit emptying, years.Fs = Frequency of desludging, years.Fn = Frequency of nightsoil collection, days.G = Factor to account for increased costs due to construc-tion difficulties because of rocky ground.H = Number of households.I = Soil infiltration rate, L/m2 /d.M = Average number of persons per household.N = Average number of households served by one unit.P = Total population served.Q = Hydraulic loading, L/person/d.S = Size of process units.T = Factor to account for increased costs due to traffic. impediments during construction.V = Sludge accumulation, m3/person/year.X = Factor to account for the type of sewage system.

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Once relative costs were established for all technologies,the next step was to allow community parameters to vary.Since costs are mainly a function of process capacity,costing functions must express the effect of varying com-munity parameters on the volume of process units (e.g. pitsand tanks). To achieve this, different methods were used foron- and off-site systems.

For on-site systems, the cost-capacity relationship de-scribed by North (1976) was used:

1. C = C1 (S / S1)m

where C1 = Known cost of system of size S1

C = Desired cost of system of size S.m = Empirical system-specific exponent (usually approximately m = 0.6).

Relationships to determine S were readily available fromliterature (e.g. Franceys et al., 1992).

For sewerage and off-site treatment works, costing func-tions were derived through power regression of data avail-able from various sources. The following example showsthe result for an activated sludge plant (cost of land notincluded):

2. C = 29080.

Additionally, for off-site treatment works, a land costcomponent was included based on estimated area require-ments.

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Recurrent costs consist of costs for operation, maintenanceand renewal. It was attempted to express annual recurrentcosts as a percentage of capital costs for the construction ofthe process units (i.e. excluding the cost of land). Since only

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relative costs were involved, it was possible to rely onfigures from a variety of locales cited in literature.

�� Table 2 outlines the costing functions for sanitation sys-tems frequently encountered in developing countries. Equa-tions were also formulated for the following systems:aquaprivy, biogas digester, bucket latrine, cistern-flushtoilet, communal septic tank, Imhoff tank, nightsoil treat-ment, pour-flush pan, pour-flush toilet with vault, primarytreatment, public overhung latrine on fish pond, publictoilet block, septic tank for excreta reuse.

��BAUMAN, H.C., 1964, Fundamentals of Cost Engineer-

ing in the Chemical Industry, Reinhold, New York.FRANCEYS, R., PICKFORD, J., and REED R., 1992, A

Guide to the Development of On-site Sanitation, WorldHealth Organisation, Geneva.

KALBERMATTEN, J.M., JULIUS, D.S., and GUNNERSON,C.G., 1982, Appropriate Sanitation Alternatives: A Tech-nical and Economic Appraisal, The John Hopkins Uni-versity Press, London.

NORTH, J.E., and PEELER, J.P.K., 1976, Techniques forCapital Cost Estimation of Water and Wastewater Treat-ment Plants. Civil Engineering Transactions, The Institu-tion of Engineers, Australia, 12-14.

WASH 1992), A Primer on Comparing and Using CostData in Water and Sanitation Reports, WASH, Arlington,Virginia.

DR THOMAS LOETSCHER and DR JÜRG KELLER,Advanced Wastewater Management Centre, Departmentof Chemical Engineering, The University of Queensland,Brisbane, Qld 4072, Australia.


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estimating the financial costs of sanitation systems

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