In a previous blog post I described start-up of a research project in Kumasi (Ghana), looking at three candidate technologies for treatment of the waste coming out of Clean Team. The idea was to identify three technologies with a) low cost, b) high treatment efficacy, c) small footprint and d) easy installation (off-the-shelf package style). So all we needed to do was identify three commercially available technologies that meet these 4 criteria, then test them in action. Easy, right?

Wrong, obviously! If you want good treatment efficacy (i.e. removal of pathogens and of the organic load that leads to eutrophication) you can do it with a small-footprint shippable package, but that’s unlikely to be low-cost. If you want really good treatment efficacy and low cost, that probably means some sort of leaching field or reed-bed or similar… large footprint, and precisely the sort of thing that people don’t want near to their homes.

Of course the team realised from the outset that technology selection wasn’t going to be easy: but I don’t think any of us predicted just how difficult it was going to be. The team (from Cranfield, WSUP and Clean Team) considered around 15 candidate technologies, and eventually selected two that best met the selection criteria: these are the Mexican Sistema Biobolsa and Luxembourg-produced Biorock. We’re also very keen to include the fascinating Ghanaian Biofil vermiculture system in our testing.

[Also of interest to us are two other technologies: the digestor/pasteuriser approach being developed by Duke University in the States, and the approach being developed by the Transforming Waste group. Neither are yet ready to testing, but both look promising: more below.]

None of the technologies selected meet all of our initial criteria. We had to accept that all will require some on-site digging, and will have a somewhat larger footprint than we’d like: at our price point that’s pretty much inevitable.

We hope to have the technologies on site in Kumasi, ready for testing, by July 2014. At this stage we’re finalising negotiations with the suppliers, and crossing our fingers! Getting the things through customs is going to be a challenge, we’re doing our best to ensure all the paperwork’s in perfect order! Meanwhile up-and-coming Ghanaian sanitation researcher Daniel Sarpong has been recruited by Cranfield to lead this work in the field, as a Masters by Research project: congratulations Daniel, great to have you on board!

Now for a bit more detail on those systems…

Sistema Biobolsa is a package produced in Mexico, centred around a tubular biodigester system, used to date mainly for animal manure, though also for treatment of sewage from low-flush toilets. Waste goes into a very simple flexible plastic tube, about a metre in diameter, half-buried in the ground; then about halfway down the tube is an exhaust pipe for collection of biogas. This is a “plug-flow” system: i.e. everything flows down together, there’s no solid-liquid separation. The final slurry coming out of the end of the tube -after about 60-90 days- goes into some sort of filter bed (to be defined). The system is very competitively priced, and that includes on-site support from the Sistema Biobolsa team for system installation.

The Biorock system from Luxembourg, likewise very competitively priced, is basically a combined septic tank and filter system. Imagine a standard prefabricated septic tank: the first chamber is like a standard septic tank first-chamber, but with capacity to harness biogas; the second chamber is a rock-filled aerobic filter, rather like trickling filter, with passive aeration. The liquid effluent is discharged directly to the environment, while solids need to be periodically removed from the first chamber.

Biofill is an exciting Ghanaian vermiculture system, and we’d like to test it as a final treatment stage for residual solids coming out of the Sistema Biobolsa or Biorock. We stress that Biofill is not currently marketed as a standalone treatment system: rather, the vermiculture component (referred to by Biofill as a Digester) forms part of an integrated toilet+treatment package (see their website). Nonetheless, we’re hoping it’ll be possible to test the vermiculture component as part of our treatment system.

One candidate technology we didn’t select for testing in this research was Duke University’s digestion-pasteurisation system. The concept behind this system is to use the biogas generated from sludge digestion to pasteurise/sterilise the liquid effluent coming out of the system: it’s an approach that has been used for treatment of livestock waste, but not yet for human wastes. It’s not yet ready for testing, but we think this concept -if it can be made to work- is remarkably elegant, we’ll be really interested to see where it goes. For more information, see the pages about this technology in the Reinvent the Toilet Fair India 2014 Technical Guide.

And finally, we’re also keeping an eye on the Transforming Waste project: these guys are aiming to use sophisticated biofilm technologies for sludge treatment, but at the same time paying very serious attention to development of a system that is low-cost and workable in developing contexts. Let’s see!

Post by Guy Norman

Guy NormanGuy is Head of Evaluation & Research. His areas of responsibility include monitoring and evaluation, technical publications, and training development. He also leads WSUP's research programme.