Thanks Kevin, your advice is invalualble as usual! I have submitted a concept note for the research I am planning. I'll get back to you if we take it forwards in this direction!

Hello Alison and everyone

I am afraid that I have been rather non-active on the forum recently - pressure of work on several other things. I would echo what Elisabeth says- that there are many terms, with subtly different meanings. I would say that the term condominial is mainly abut the approach to construction and management - although as used in Brazil it does imply the range of technical standards and approaches that are commonly referred to as simplified sewerage. The key points about simplified sewerage are its adoption of small diameter sewers (100mm) and relatively flat gradients. Its proponents argue that conventional sewers are over-designed and that smaller diameter sewers are hydraulically more efficient. I am doubtful about the theoretical justification for flatter gradients and I think that the smaller diameter argument normally requires that the sewer acts as a closed conduit with no influx of storm run-off, both of which are difficult to ensure in practice. I can share notes on this if anyone is interested.

The Orangi Pilot Project is often quoted as an example of simplified sewerage but its approach differs in many ways from that developed in Brazil. There is no emphasis on small diameter sewers - most are 9" or 227mm diameter. OPP has no coherent approach to minimum sewer slopes - in some of its literature it says 3" in 100' (1 in 400). In other places, it suggests that using the rule of thumb that the slope should be 1 in the diameter of the sewer in mm (so a 150mm sewer should be laid at a minimum slope of 1 in 150 and so on. The first criterion results in sewers that will definitely silt while the second is not practical where the topography is flat and is not followed in practice by OPP. I would not say that the OPP implementation system is particularly complex - they encourage people to appoint a 'lane manager' who is responsible for implementation on behalf of the community. OPP itself does not handle cash. The approach is actually not so different from what people have always done informally in unplanned areas in Pakistan - see our book on Urban Sanitation Planning for a brief explanation of this.

Solids free sewers (I really dislike the term settled sewerage - it suggests that the sewer pipes are settling) are different again in that the idea is that solids are settled out in interceptor tanks before reaching the sewer. Some of the sewers in Pakistan use this approach - Mr Ahmed Nazir Wattoo in Faisalabad, who follows the basic OPP approach with some modifications and improvements, argues strongly for the provision of small interceptor tanks and I think there are good reasons for including them in a scheme, even if they are never emptied.

I have a lot of information on various low-cost sewer schemes, all involving shallow sewers, at least at the head of the system. Alison, I can share my material with you - there is so much information out there already, the main challenge is to make sense of it all. Gabrielle Watson's publication ;Good Sewers Cheap is particularly good on Brazilian condominial systems and what works and does not work. Duncan Mara edited a book on low cost sewerage in the mid 1980s, It may seem old but the situation has not changed and the lessons from that are still valid. (I must declare an interest - I have a chapter in the book).

I hope that this is helpful

Regards
Kevin

Thanks Elisabeth, this is really useful. I'm putting together a very early stage proposal on the topic. It may come to nothing, but let's see!

Hi Alison,

Perhaps this forum thread started by Aasim in India is also useful for you:
forum.susana.org/forum/categories/165-ce...tled-sewerage-system

He was looking for case studies for settled sewerage systems, and got 4 replies.

Is there a specific reason why you asked this question? Are you working on this topic now?

I think one problem we're having is that there are so many terms for similar, the same or different systems, like condominial, simplified, settled sewerage, septic tank effluent sewers... I've tried in the past to at least clean things up a bit on the various Wikipedia articles but it's not easy... Any help would be appreciated. This is a reasonably good entry page:
en.wikipedia.org/wiki/Sanitary_sewer

Regards,
Elisabeth

Thanks Remi, this is really useful!

Hi Alison. Ps-Eau did a wonderful review of such systems worldwide a couple of years ago, and produced some guidance too. It's on www.pseau.org/en/non-conventional-sewerage-services

Below is a short "reading note" I did for colleagues in WaterAid:

What struck me in the review:

I enjoyed in the main report on page 19, the figure comparing different kinds of sewers, and on page 88 the required levels of maintenance.

Alternative sewers are 30 to 50% cheaper than conventional ones, but still 50 to 70% more expensive than on-site sanitation, contrary to earlier claims, because maintenance is still a huge need.

The main cause for failure is not technical problems (although they are common – slope, leaks…), but management and especially lack of skills in the utility, in terms of billing, marketing, community engagement, M&E including sanctions, and technical maintenance. Community management has consistently failed, however community engagement has often been crucial.

There are many conditions of success including: good solid waste management (to prevent blockages), good rainwater drainage (to avoid overload), actual demand for such a system (what is it that communities actually want?); an existing culture of sewers (driving demand and a habit of paying bills); integration in strategic city planning, and with other infrastructure (like road building, land regularisation…); having a special operator or department in charge of the sewer.

Financially, many systems are running at a loss, but it is usually an issue in management (which would affect any system). There are interesting solutions such as charging for the sewers together with solid waste management rather than water, which is more acceptable in some cases.

The well-known case studies are often misleading:

• OPP in Pakistan (a WaterAid partner) has done many simplified sewers for about 2 million people, but requires such specific community mobilisation techniques that it has hardly been replicated.
• Some African countries have been pioneers (Nigeria and Zambia in the 1960s) but have often failed because of low fee collection, too few connections, and under-estimation of operational costs.
• Conversely, some are well functioning but not well known, like Ramagundam in Andhra Pradesh.

Finally, the guidance manual is useful when discussing with municipal planners and engineers; especially part 4 on maintenance helps to see the required capacities that need to be developed before implementing such systems.

Are there any recent reports in English assessing the latest in condominial/simplified sewerage, specifically the extent of current implementation. Most of what I can find is nearly 10 years old now!

The guide (called pS-Eau guide n°7. Non-conventional sewerage services. When to choose this option, how to implement this solution., J.M. Ily, C. Le Jallé, J. Gabert, D. Désille, pS-Eau, 2014) and the other outputs of the study on “non-conventional sewerage services” are available via this link in English and French:
www.pseau.org/en/non-conventional-sewerage-services
Comments are welcome.

Best regards,
Christophe Le Jallé