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Cost effectiveness comparison between sewerage and on-site sanitation

We have received a request for a list of (academic) studies on comparisons (cost effectiveness) between conventional (piped) sewerage systems and on site sanitation solutions.

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Below is an annotated bibliography on this topic compiled by my IRC colleague Senior Programme Officer Erick Baetings.

General observation Research and studies seem to be limited both in terms of spread (number of cities) and depth (number of different types of sanitation technologies). For example where onsite sanitation technologies are included, the costs for emptying, transport, treatment and safe disposal or reuse may not have been considered. Furthermore full life-cycle costs may not have been considered.

What did I find?

[1] Daudey, L. (2017) Journal of Water, Sanitation and Hygiene for Development (2017) 8 (2): 176-195. . It may not come as a surprise but the paper concludes that “conventional sewer systems are in most cases the most expensive sanitation options, followed, in order of cost, by sanitation systems comprising septic tanks, ventilated improved pit latrines, urine diversion dry toilets and pour-flush pit latrines. The cost of simplified sewer systems is found to be lower than both conventional sewer systems and septic tank-based systems”.

See fig.4 on the Annual lifecycle costs per capita of centralised (conventional) and simplified sewerage, and septic tank based FSM systems (full sanitation chain).

[2] WSUP (2018) Comparing the costs of different urban sanitation solutions in developing cities in Africa and Asia.

This is two-page policy brief that was developed on the basis of the desk study carried out by Loic Daudey (see above).

[3] Hophmayer-Tokich, S. (2006) Wastewater Management Strategy: centralized v. decentralized technologies for small communities.

This paper concludes “Whereas the conventional centralized strategy, developed in the middle of the nineteen century and spread out ever since, proved to be very efficient in pollution control and became the preferred strategy on planners and decision makers, it is growingly recognized that this strategy cannot be feasible in many cases. This is mainly due to high costs of transportation systems, especially in low population density areas and in very poor communities. Low capacities of these communities to implement and manage these facilities, is another constraint. As a result, the previously discarded strategy of on-site treatment is growingly becoming popular and accepted.”
Although the paper does not provide any cost comparisons, it does compare centralized and decentralized technology solutions. The paper highlights two main constrains for the provision of adequate wastewater treatment: high costs and institutional low performance.

What is interesting in the paper is that it comes up with a list of factors that should be considered when selecting the right solution: 1) water consumption rates; 2) wastewater production volumes; 3) population density; 4) local groundwater contamination risks; 5) soil permeability; 6) existing infrastructure; 7) cost of systems and affordability of the target community. Other more qualitative factors, such as social considerations and institutional capacity, should also be considered.

[4] Cairns-Smith, S., Hill, H. and Nazarenko, E. (2014) Urban Sanitation: Why a portfolio of solutions is needed; Working paper. ... (more)

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