For reference:
web.sbe.hw.ac.uk/staffprofiles/bdgsa/tem...UD/PDF/PAP005300.pdf
Is an short report on the problems faced in Cape Town (as I said, mainly higher level management problems and less technical ones).
Thanks for the GTZ paper and the other links!... the GTZ one seems similar but a bit more detailed than the one linked
here from 2005.
I am currently working as a PhD level researcher in the Department for Sanitary and Environmental Engineering (DESEE) at the University of Kassel in Germany.
We are not working on vacuum sewer system right now, but rather the application of gravity driven ultrafiltration membranes for emergency use in developing countries.
But due to our experience with decentralized waste-water treatment plants in Germany and sewer systems in general, I am currently proposing to have a closer look at vacuum sewer systems combined with DEWATS in a development context (somehow...).
But as I mentioned in the WASH forums, this is at an brainstorming level only right now, but I see some potential in rethinking the use of vacuum sewerage technology as following:
1. Current systems often include house installations and focus on a completely automatic operation as comparable to "flush and forget" systems found in industrialized countries. While this has obvious advantages from a user point of view, it drives up costs significantly (especially the HH automatic vacuum valves are costly) and is not mandatory for a functioning vacuum based faecal sludge management system (see below).
2. Current system know only one level of service (direct HH connection), while redesigned systems could have different levels depending on HH income and could offer later upgrades between different levels (as well as allowing for tarif cross-subsidy between different level of income). Different levels could go from HH level, to community latrine blocks, to HH but manually operated, to interval vacuum desludging of septic tanks with a flexible hose connected to the system at the nearest road junction and so on. Here is especially the easy expandability and semi-temporal nature of interest for slum settings. Furthermore this adheres to the concept of an early adaptors and progressive upgrade idea much closer than other (often more individualized) sanitation approaches.
3. Combination with DEWATS biogas plant either at the central point where also the vacuum station is (with use of biogas for electricity and vacuum co-generation), and/or at several further decentralized locations with only a vacuum (and maybe biogas) and not a sludge transfer (or liquid only for nutrient reuse?) through a much smaller diameter pipe or flexible hose. Transferred vacuum could be used both to desludge several HH intermediate tanks into decentralized biogas DEWATS plants and also as an easy reactor mixing method to increase bio-gas production.
4. Redesign of vacuum-stations with locally available and off the shelf parts (f.e. motorbike engines or similar; run with bio-gas) and locally producible (and repairable) liquid ring vacuum pumps (proven, extremely simple and nearly maintenance-free design). Cheap electricity co-generation also possible for income generation and community supply. Also a question: is is possible to build vacuum tanks out of ferrocement? Are there other means of re-using equipment for vacuum production (AC compressor pumps, car engine turbo-compressors?)
5. Measures to save water as vacuum severs need much less water, would make it rather interesting for areas with no or only communal tap-stand level water supply. Furthermore vacuum sewer systems can be build pretty flood-safe as vacuum station and waste-water treatment plants can be located at an somewhat elevated position (and pipes are water proof).
6. Creative re-use of existing vacuum pumps (as for sewer systems, pumps have to run only a few hours a day): vacuum pump supported air moisture collection and compression dewing (with higher vacuum levels even distillation at ambient temperatures is possible) for save waste-water reuse and sludge pre-drying (rotary vacuum sludge dewatering is also possible, but probably with higher maintenance needs). Even desalination would be possible, but probably of lesser economic relevance.
7. Creative re-use of existing vacuum pumps: bio-gas upgrading through CO2 and H2S removal with pressurized water stripping (for gas sale and better utilization in engines) & better gas storage through increasing pressure in storage tanks.
8. Minor aspects: Due to suction of air at pit, smell problems of cheaper toilet designs could be nearly eliminated and thus acceptability greatly increased. Besides that, use of an apparent "high-tech" system (but not necessarily so in reality) might make such a system much more attractive (e.g. small tarif "worthy" and thus maintainable) to progress oriented urban inhabitants (something many other "low-cost" solutions lack).
And so on... as I said still at brainstorm level.
Obviously not the absolute cheapest solution, but benefits might justify the investments costs (which can be made lower as proposed above) even for low income countries and potential for progressive cost recovery is high.
Anyways... tell me what you think!
