.. as already indicated by Marijn, I would recommend that we do not try to specify a complex service chain with central or decentral treatment and central or diverse management through one acronym (centralised, de-centralised, on-site)...

While you talk of a sanitation system, describe the user interface, the conveyance, the treatment, the management system and after the description give it a 'name' which you then use in the further text... in doing so we can avoid any misunderstanding...

..maybe except for 'centralised sanitation system' as a synonym for 'flush toilets, sewers and centralised wastewater treatment plants' sanitation systems have become so diverse that a single acronym can no more describe them comprehensively...

ciao, Hajo

Looking at it from a DRR or system sustainability approach it would be maybe appropriate to define it via the resilience to the breakdown of central management?

Dear Elisabeth, Joe, Hajo

I think, most people would think of the primary treatment step when interpreting a term like "centralized sanitation". And would assume a sewer and WWTP based system.

The treatment based classifications that Hajo gives in his post seem well established to me. However, they are very technology centric (while in many cases, the management aspect is probably more critical). I think those classifications are only practically useful when describing a well known system and may cause confusion when describing a system that is different from one that is used in "the West/North".

While I think it is logically correct to describe a non-sewer based system comprising of toilets, trucks and a centralized treatment plant as "centralized sanitation" I also see how the term would put people on the wrong track.

In the end, it is probably up to the author to find a good name for a system. The name would have to consider that the terms as Hajo presented have strong connotations in terms of the primary treatment step, and conveyance and management systems as found in Europe and the US. So if you describe a system that is different from one of these, you should make it somehow clear in the term you use for it.

For example: "non-sewer centralized sanitation" for the system mentioned above. For eTekwini I would probably say "centrally managed waterless sanitation" as that covers the most important management, technical and primary treatment aspects.

Regards

Marijn

yes, I am an engineer and therefore my defintion will be guided by that view..

but we should also consider making things easier for us and therefore I propose to make the differentation between 'on-site', 'decentralised' and 'centralised' purely along technical lines:
on-site: pit latrine, VIP, UDDT, (pour-)/flush with pits or septic;
decentralised: (pour-)/flush with localised (perhaps simplified/no-solid) sewer network and DEWATS;
centralised: flush with city-wide (conventional) sewer network and central WWTP.

I know that even with this definition, you may still have 'grey' zones with 3 or 4 networks/WWTP in a mega-city. Is that centralised or de-centralised (I tend to the first)?

But let us not make defintions more difficult by introducing the managing system as criteria. Otherwise you may have to call a system 'technically decentralised with central management' (80,000 UDDTs under EWS).

ciao Hajo

Could you describe what a "totally centralised urban city-scale system" might consist of with respect to technology and management model? Can it be a mix of technologies?

I think the point is about the scale of the system. A large water treatment works which processes a large amount of faeces is a centralised system, even if there are also people in the city who are not plumbed into it.

Stenström et al are using it in this way in this doc:
www.susana.org/_resources/documents/defa...hnologiessystems.pdf

(Semi-) centralized treatment technologies are normally designed to accommodate increased volumes of waste and provide improved removal of nutrients, organics and/or pathogens than household-centered collection and storage technologies. The technologies in this section serve large groups of houses, small communities and in some cases, cities. The differentiation between semi-centralized or centralized depends on the design
of the technology, the number of people served, and the management model that is employed.

Ha. Well, I think I'd be talking about unmonitored decentralised systems vs a properly-managed centralised system, so would say that the eThekwini is more like a centralised than a decentralised system, at least to the extent that there are people with authority and skills managing the whole thing.

But you are right, maybe this whole paradigm breaks down under analysis.

But is your definition of "centralised" based on the technology used or based on the management aspects?

Example: are the 80,000 UDDTs (serving around 400,000 people) that are scattered around the peri-urban areas of Durban and built, managed, serviced and to some extent monitored and nowadays also emptied by the EWS (eThekwini Water and Sanitation Unit of eThekwini Municipality) in your opinion a centralised system or not?

Could you describe what a "totally centralised urban city-scale system" might consist of with respect to technology and management model? Can it be a mix of technologies?

I might be totally wrong, but I tend to see it as a spectrum - with totally centralised urban city-scale systems at one extreme and individual UDDT etc at the other.

I was generally talking about something that works for 1000 to 10000 households, would you describe that as centralised or decentralised? Personally I don't think faecal composting really works very well at scales smaller than that.

What is everyone's definition of a centralised sanitation system?

When I hear that term I automatically think of flush toilets, sewers and centralised wastewater treatment plants. Is that valid?
Or does the term "centralised sanitation" really exist? We have "centralised wastewater treatment" and we have on-site sanitation and we have decentralised sanitation, but I am not now not so sure about the term centralised sanitation.

I am asking due to a discussion I had with Joe which started off discussing the Wikipedia article on composting toilets...

If we come up with a good definition of censtralised sanitation then I could also add it to the Wikipedia page on sanitation (the content of which was partly written/edited/re-arranged by me):
en.wikipedia.org/wiki/Sanitation

I checked the glossary of the eCompendium but the term is not included in there:
ecompendium.sswm.info/glossary/3#letterc

Thoughts anyone?

Regards,
Elisabeth