Anaerobic systems

I keep coming across more than quite a bit of confusion here! So let’s be clear. Septic tanks were first developed in France in the 1860s by Jean-Louis Mouras. Donald Cameron used them in England in 1895 (see his “Monster Septic Tank” here). What happened next? Well, Imhoff tanks came on the scene in 1906, though these were too big for individual use (prefabricated units are still available for up to 1000 p.e. − details here).

Quite a bit of research on septic tanks was done in the1950s by the US Department of Housing (important as around a third of US households are served by septic tanks) – the main emphasis was on how many compartments it should have. I’ve lost/can’t find most of these reports but my memory is that it was found that two compartments were better than one but that three weren’t better than two (nor were four or five, etc.).

Upflow filters were then developed in India to ‘polish’ septic tank effluents − see Upflow filters for septic tank effluents by V. Raman and N. Chakladar (Journal of the Water Pollution Control Federation 44 (8), 1552−1560, August 1972). I think these are excellent!

Then came the next septic-tank development: the UASB – upflow anaerobic sludge blanket reactor (developed by Professor Gatze Lettinga of Wageningen University in the 1970s): the influent is introduced across the reactor base and flows upwards, through the sludge layer, to the effluent weir; biogas can be collected if so desired. [Gatze Lettinga said to Barbara Evans, who works with me at Leeds, ‘why are you going to Leeds to work with Duncan Mara – he’s mad’. I take this as a compliment as I’ve “seen through” UASBs!]

A PhD student of mine, Professor Miguel Peña Varón, developed the high-rate anaerobic pond (HRAnP) to combine the efficiency of UASBs with the simplicity of anaerobic ponds (he also showed that conventional anaerobic ponds were ‘better’ than UASBs – see here).

Then came DEWATS − Decentralized Wastewater Treatment Systems – which typically comprise a ‘settler’ (a two-compartment septic tank) and an ‘anaerobic baffled reactor’ (ABR) (basically a baffled septic tank), followed by an anaerobic filter and a ‘planted gravel filter’ (i.e., a horizontal-flow constructed wetland). There’s the Decentralized Wastewater Treatment Systems (DEWATS) and Sanitation in Developing Countries - A Practical Guide which will set you back €48.75 plus postage (€12 outside Europe)!

On ABRs see The evaluation of the anaerobic baffled reactor for sanitation in dense peri-urban settlements, a WRC report dated 2006. Part of the report’s recommendations: “The ABR is able to provide better and more efficient treatment of wastewater than a septic tank. Therefore it is recommended that an ABR system can be used in any situation that is considered appropriate for a septic tank.” I don’t think I agree with this somewhat sweeping recommendation!

This is getting a bit too much into wastewater treatment (rather than sanitation per se), so why not have, for a small community a two-compartment septic tank (with the influent entering across the base of the first compartment), or for a larger community a high-rate anaerobic pond, then a secondary facultative pond + an aerated rock filter? Not sure I care much for UASBs, DEWATS or ABRs. Well, I thought I’d just mention it.

Research imperialism/nepotism

What on earth is “research imperialism”? It’s a phrase I use to describe the situation whereby a researcher from an industrialized country with his or her pockets full of research dollars says to a more impoverished researcher in a developing-country university “Come on, let’s research this, I’ve got the dollars, and the funds will cover a trip or two by you to my university”. This is OK, of course, if the research topic is of genuine interest to both parties, but not if it’s only of real interest to the industrialized-country researcher. However, the developing-country researcher might well be tempted to go along with it as it will most probably look pretty good on his or her c.v. and the trip to Europe or the USA (or wherever) would be pretty good too. Does research imperialism exist? You bet it does! Constructed wetlands in East Africa, for one.

Say No to research imperialism!

And what about what I call “research nepotism”? Possibly even worse than research imperialism, research nepotism is giving large chunks of research money to your mates – and this includes people like your PhD supervisor. Does this occur? You bet it does! [Does Bwana Bill know? Sijui.]

Say No to research nepotism!

Latrines more expensive than sewers!

I normally assume that low-cost sanitation technologies are cheaper than conventional sewerage. Not necessarily so, at least according to Sophie Trémolet’s presentation “Effective Public Finance for Sanitation: A study for WaterAid” presented at the IRC Symposium ‘Pumps, Pipes and Promises: Costs, Finances and Accountability for Sustainable WASH Services’ which was held in The Hague from 16−18 November 2010. Here’s part of what she said:

In Dar es Salaam, the Government chose to concentrate 99% of public funding on building network sewerage and sewage treatment facilities, even though these systems benefit only 10% and 3% of the city’s population, respectively. Household on-site sanitation receives very limited funding for software support[which is] provided in a decentralised and uncoordinated manner, with no evidence of impact. This results in an inequitable situation, as the costs to households of building and maintaining a latrine are about 2 to 3 times higher than those of a network connection [emphasis added]. Public funding for the sanitation sector in Dar es Salaam is therefore not effective, as it does not significantly increase coverage, achieve environmental results or improve public health.

So latrines can be more expensive than sewerage. Ain’t that really strange!

►All the presentations made at the IRC Symposium are available here. Quite a few are well worth reading, especially those on costs.

Right advice?

How do you know that you’re getting the right advice? EcoSan toilets? Arborloos? DEWATS? UASBs? Even simplified sewerage? Do you, can you, trust the person(s) giving you this advice? Well, there’s nothing like knowledge – at least the knowledge that you should query all advice given to you. If you don’t know all the sanitation alternatives in detail (where they’re appropriate, how to design them, how much they might cost), then you need to find out about them and then query the advice you’ve received – for example you could look at Urban sanitation planning: A technology check list for planners or Sanitation for a healthy nation: Sanitation technology options (DWAF, Government of South Africa, 2002) [there are, of course, other publications but these two are at least both concise and comprehensive].

Let’s make 2012 the Year Of Good Advice!

Sewer gradients 2

The Orangi Pilot Project (OPP) in Karachi, Pakistan is a very well known low-cost sewerage project, but what is not so well known perhaps is that the site gradients in Orangi were greater than the minimum required sewer gradient, so hydraulically at least the project was bound to succeed. However, when this low-cost sanitation technology was applied in other cities in Pakistan, problems occurred as the site gradients were lower than the minimum sewer gradients.

I remember, after I gave a talk on simplified sewerage some years ago at a WaterAid meeting in London, a young woman engineer from OPP came up to me and asked if I’d go to Karachi and teach OPP staff how to design sewers! Well, nothing came of that, other than a realisation on my part that sewer hydraulics are incredibly important – a fact that really needs to be more widely appreciated.

Sewer gradients

I’ve been told that simplified sewerage projects haven’t worked well in Sub-Saharan Africa. Is this because they’ve been run by NGOs with little or no previous experience of sewerage? Possibly. Here’s a test for you: due to ground conditions you have to have a sewer gradient larger than 1 in 200. Would you go for 1 in 300 or 1 in 100? [Simple if you’re an engineer, but maybe not if you’re not?]

Tempus fugit!

Time passes. A few excuses: quite a bit of work, despite retirement; some ill health; a lot of grandparenting; and a few spells of general indolence! But I’m more or less back on track, so watch this space again.