Actually, there are also „DEWATS“ that don’t work in warm climates. This is always a good opportunity to learn.

Like with computers: the problem often sits in front of the screen. But differently from computers - in wastewater treatment we are dealing with living organisms and their metabolism - it is all about a caring relationship. Few people dare to engage closely in this kind of relationship.
There are also many bicycles that don’t work in cold climate (and it’s not because of the cold climate).

True: temperature matters for anaerobic systems - lower efficiency is taken care of by larger volumes of the treatment units.

But „DEWATS“ is more than the anaerobic modules - constructed wetlands or planted gravel filters, as we call them, are much less sensitive to cold temperatures.

This kind of discussion is yet another reason for the existence of the SuSanA online forum

Regards
Stefan

Hi Qasem, nice to see you here on the forum. I think you are raising an excellent point and it would be very interesting to hear more from your side about the functioning of the DEWATS systems in the cold season. What are the operational and/or institutional challenges you are facing? How does this, in your opinion, differ from the DEWATS system you saw in India a few years ago?

From my understanding, BORDA started implementing DEWATS systems in Afghanistan in 2012/2013, mostly on a mid to large scale (50 to several thousand users) in schools, hospitals, mosques, offices, etc. Disposal of the final effluent is either into existing sewers (if applicable), in constructed percolation beds (to prevent surface run-off) for dispersal or sometimes reused for irrigation. From the projects I am aware of, I think none was using a planted gravel filter (space restrictions and climate possibly). Primary sludge production might be an issue, especially if the settler is not desludged regularly... and where to with the sludge then anyway, right? Would be great to see some more data and facts about the systems in place.

I second that replacing traditional dry toilets with water based cesspits might not be the best option on a city-wide scale if there is no proper treatment provided down the line.

As Dean was proposing, vermidigesters might work more efficiently on a single household basis, right? Or how would a scaling up strategy work there for larger institutions? The Anaerobic Filter in DEWATS is not, as Dean suggested, intended to remove remaining suspended solids, but rather a fixed biofilm reactor to digest remaining organic pollution and dissolved solids.

I really like the idea and application of vermifilters, but are there any experiences of how the recirculation digester works when there is a power cut or no electricity available? Can solar panels be easily and securely installed in a urban setting like Kabul (I would think about replacement parts and potential theft or the intention to rewire the whole thing and use the electricity for other purposes)? I also suppose, with temperatures of -15 degC, there must be some sort of insulation around the pipes? And what about the worms?

The BORDA DEWATS system uses traditional proven and simple methods, but perpetuates the same old issues and problems with such traditional decentralised and centralised systems:

1. Sludge
2. Maintenance

Yes, a great idea to use anaerobic digestion processes and harvest the gases, but is the methane actually being valued or used? If not, the system just contributes to global warming.

Capacity appears to be an issue in Kabul, with those few cooler months requiring greater capacity, thus higher costs of construction per user. Pushing limits is human nature, in this case with some potentially unpleasant consequences...

How well are the filters being maintained? The anaerobic filter units must be rather unpleasant to remove and clean, and the planted gravel filter would require periodic media replacement to remain working effectively. These maintenance operations would require scheduling and implementation. Could the BORDA people please provide details on their maintenance schedules?

How is the sludge dealt with?

Nothing is provided on the BORDA website regarding what happens to the treated effluent. Is this disposed of to land, to surface, to subsurface or to water table?

I would suggest that in most cases a DEWATS is not necessary, unless dealing with all domestic wastewater (not just blackwater). A simple vermi-digester is an inexpensive and simple method for dealing with just blackwater. However, where wastewater treatment needs to be taken to the next level, I'd like to compare and contrast the anaerobic BORDA system with an aerobic biodigester.

The BORDA system starts with a septic tank (step 1), producing lots of sludge by settling most of the solids, and liquid effluent that has no dissolved oxygen remaining. Then an anaerobic baffled reactor (step 2) removes suspended solids as more sludge, while generating nitrous oxide and methane (both potent greenhouse gases). Then an anaerobic filter (step 3) is added, I assume because the wastewater still has excessive levels of suspended solids (more sludge) before finally going through a planted gravel filter to remove remaining nutrients and to aerate the effluent for disposal. All so last century...


BORDA Decentralized Wastewater Treatment System

In contrast the aerobic biodigester is aerobic in all stages. Step 1, removing the solids, which decompose aerobically and rapidly to 1/10th original volume. Then step 2, aerobic baffled reactor series to settle suspended solids, (which does generate some sludge, but this sludge is pumped back periodically into stage 1 for aerobic decomposition into humus). Then stage 3, recirculation, bio-filtration and aeration. Simple and elegant.


Figure 2: Aerobic recirculating biodigester

What is innovative? Unlike traditional aerobic DEWATS, aerators are not used. This is because aeration pumps require considerable energy per unit of wastewater for removing oxygen demand. Instead, a trickling vermifilter is used with a very small recirculation pump, i.e. pumping water instead of air. Trickling water through an aerated medium provides a huge surface area for dissolving oxygen into the water. Experiments with my own domestic system have demonstrated that about 1 watt per person is required for the recirculation water pump, about 1/10th of the energy used for equivalent aerator pumps.

I appreciate that the anaerobic BORDA system requires no energy, but capital costs are likely to be much higher because of the significantly larger capacity required. The aerobic recirculating biodigester, on the other hand, requires a small amount of electrical energy but for the same capacity can process more waste. The pump is easily and inexpensively powered by solar panel (technology of this century). The system also produces easily extractable stabilised humus rather than active sewage sludge. Additionally, the vermifilter is self-maintaining because of the combined activities of micro-organisms and earthworms.

Looks to me like the BORDA system could be very easily adapted into an aerobic recirculating digester, provided the users want processing efficiency rather than methane.

Vermifilters are an exciting new, yet simple technology for wastewater treatment. Sludge generated from soak pits, septic tanks and anaerobic DEWATS systems will only grow as a problem until replaced by smart, low cost aerobic alternatives.

Hope this helps.

cheers
Dean

Dear Qasem,

This is a very interesting discussion thread, thanks for having started it.

You said:

The decentralized treatment system which is introduced by BORDA in Afghanistan dose not work properly in cold season.

Could you please provide us with more information about this problem? I would have thought with the right design parameters, DEWATS systems can also work in colder climates.

I will also alert SuSanA members working for BORDA to this thread so that they can comment, as well.

And I thought I would mention some resource:

• Wikipedia article about water supply in Afghanistan (probably in need of updating!):https://en.wikipedia.org/wiki/Water_supply_in_Afghanistan
• Documents in the SuSanA library dealing with groundwater pollution in Kabul (there are quite a few because BGR was doing research on this topic for a number ob years):
• This link brings up documents after searching for keyword: Kabul www.susana.org/en/resources/library?search=kabul
• And this brings up the documents after filtering for Afghanistan as a country (includes some documents on Herat, where GIZ was active): I can't get the link to work properly but just go here and filter by country Afghanistan by using the green filter button: www.susana.org/en/resources/library

Hope this helps a little bit.

Regards,
Elisabeth

P.S.
Dean had asked:

What do the 97% do, how many of these use onsite systems (septic tanks etc)?

Those 97% would be using onsite systems, i.e. septic tanks, pit latrines, perhaps also some public toilets? I have no idea of the proportions though - perhaps you could say something about that? e.g. 25% septic tanks, 25% pit latrines etc.

Hello,

We manufacture decentralized sanitation solutions designed for handling human solid waste. They are built into a shipping container in order to allow them to be transportable.

We recently manufactured and provided a decentralized human solid waste processor for Kivalina, Alaska to handle -40C/F. The AK project was designed to handle waste input from UDDTs and Honey buckets.

We have additionally done systems in India designed for handling sludge.

You can read more about the project here:
www.biomasscontrols.com/alaskan-deployment

If you have any questions please let me know! You can always reach me at This email address is being protected from spambots. You need JavaScript enabled to view it. as well.

Where temperature limits biological processes you just need capacity.

For biological onsite systems some water is required. Each time someone defecates, a minimum of one cup of flush water is required for vermi-digesters (the simplest, cheapest treatment system). Then there are UDDT's.

Why did the people do away with dry toilets in favour of cesspit toilets? A "cesspit" or soak pit is both difficult to empty and likely to contaminate the water table, simply because of its depth. Dispersal rather than concentration is the No. 1 rule for wastewater disposal to land and onsite systems need some land area for soakage. I've attached a diagram of a simple vermi-digester, showing a wider, shallower soakage field than with a soak pit. Unlike with a soak pit the volume of solids is reduced to 10% by composting worms and the humus is easy to remove.




Figure 1: Simple vermi-digester toilet

cheers
Dean

Dear All

Thank you so much from your attention.

Situation of Kabul

average precipitation 300 mm/yr
temperature in winter goes minus 15 and in summer goes 39 degrees Celsius.

The present water-supply infrastructure system is inadequate. Merely 12% of Kabul residents have
access to an appropriate water supply, 50% rely on private wells, and the remaining 38% rely on
private water-supply companies and public wells. The groundwater level dropped over the past
decade throughout most of Kabul, especially in the highlands. Groundwater showed a high
concentration of nitrate in some places, especially in the lowlands.

The sewage systems are also poor. The wastewater treatment services are almost zero. Cesspit toilets replaced dry toilets during the past decade. The lack of a wastewater treatment system and changes in toilet type may have caused groundwater and surface water pollution. Kabul must urgently protect its drinking-water sources from pollution and improve its sanitation system by establishing a wastewater treatment system

So based on the background of Kabul city its need it to develop a onsite or decentralized system for urgent solution of the wastewater problem

Your suggestion and support is highly appreciated.

Best regards

Dear Qasem,

There was one publication on composting toilets in remote and cold areas by Geoff Hill. You can find it in SuSanA's library here: An evaluation of waterless human waste management systems at North American public remote sites

I am not suggesting the solution is composting toilets (the conclusion was that the degradation of fecal matter was not so good because of the cold temperature). However, the author of the report might be a good resource person to contact and give you advice on sanitation solutions in cold weather.

Best regards,

Cecile

I agree with Marijn's observations.

Is running water available throughout Kabul?
What do the 97% do, how many of these use onsite systems (septic tanks etc)?

Dean

CSE India documented select case studies that present innovative, sustainable and affordable ways treating the sewage locally including reuse/recycle.

www.cseindia.org/node/3798

Dear Qasem,

With so little information regarding the poorly functioning projects you mention it will be very hard for anyone to advise you concretely. I am sure you are aware of the fact that the BORDA systems, and practically all other low-tech approaches depend on natural (bacterial) processes. Since such processes slow down considerably with lower temperatures, special care needs to be taken when adapting the technology to colder climates. I am not enough of an expert to give an answer to the question of whether those technologies would work at all in Kabul if re-designed. But in general, engineers designing such systems for your environment would have to change some of the parameters in their calculations to accommodate the lower temperatures. The end result will be larger systems for a given amount of waste water.

If you search through the old DEWATS threads on the forum, I am sure there are some contributions from people who have designed similar systems in low temperature environments (I think in Ukraine).

Regards

Marijn