Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)
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Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 17 Jan 2017 15:59 #20142

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    cecile
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Note by moderator (EvM): Cecilia is answering here the post of Marina who has temporarily been banned from the forum until we sort out some issues (awaiting her reply). This was the question that Cecile is addressing:
Most of the ​cities in ​Afghanistan are ​built without a ​proper sewage ​system, for ​example: Kabul ​is a ​metropolitan ​city with only ​3% of the ​houses ​connected to ​sewage and ​treatment plant.​

97% of the ​city does not ​have sewage ​systems and ​treatment plant ​for wastewater ​and they only ​collect the ​toilet ​wastewater.

What do you think is the best treatment solution for a city without a centralized sewage system?


+++++++++

Dear Marina,

I would heavily rely on the Compendium of Sanitation Systems and Technologies to support research and action on which technologies are the most appropriate to the context and which tackles the whole sanitation chain. It is complemented by the CLUES manual for planning.

I would also look at Sustainable Sanitation in Cities, a framework for action (edited by SuSanA), which includes case studies based on Compendium's approach as well as planning.

Another very useful document is the Key Elements for a New Urban Agenda by Borda which reflects on the experiences of several stakeholders including gender sensitive sanitation which might be an interesting approach in the case of Afghanistan.

I hope this helps.
Cecile
Cécile Laborderie
MAKATI Environnement
Last Edit: 20 Jan 2017 13:38 by muench.
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Reply: Best decentralized treatment solution for a city without a centralized sewage system? 20 Jan 2017 05:23 #20178

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    qasem120
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Dear Cecil

The decentralized treatment system which is introduced by BORDA in Afghanistan does not work properly in cold season. If you know a better decentralized system for cold region please let me know.

Best regards

Qasem Brati
Last Edit: 29 Jan 2017 09:44 by qasem120.
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 21 Jan 2017 08:58 #20187

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    Marijn Zandee
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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
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 21 Jan 2017 13:08 #20188

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    Bhaskar
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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
Clean technology promoter.

I am working on a clean technology product to grow Diatom Algae in large waterways. Diatoms account for about 25% of all photosynthesis on Earth and hence are the best solution to consume CO2, N and P and oxygenate water and feed fish.

I am a Chartered Accountant but am now an entrepreneur focussed on clean technology.
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 22 Jan 2017 03:29 #20192

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

Dean
Dean Satchell, M For. Sc.
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Last Edit: 22 Jan 2017 03:30 by goeco.
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 22 Jan 2017 13:34 #20193

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I agree with Marijn's observations.

Re: Reply: Best decentralized treatment solution for a city without a centralized sewage system? 23 Jan 2017 11:18 #20203

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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
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Re: Reply: Best decentralized treatment solution for a city without a centralized sewage system? 24 Jan 2017 06:12 #20209

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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
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Re: Reply: Best decentralized treatment solution for a city without a centralized sewage system? 24 Jan 2017 08:55 #20211

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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
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Last Edit: 26 Feb 2017 02:49 by goeco. Reason: add image rather than just link to it.
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Re: Reply: Best decentralized treatment solution for a city without a centralized sewage system? 24 Jan 2017 21:38 #20216

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    JessP
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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 e-mail address is being protected from spambots. You need JavaScript enabled to view it as well.
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Re: Reply: Best decentralized treatment solution for a city without a centralized sewage system? 26 Jan 2017 14:53 #20237

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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!):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.
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Last Edit: 26 Jan 2017 14:58 by muench.
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Re: Reply: Best decentralized treatment solution for a city without a centralized sewage system? 27 Jan 2017 08:05 #20249

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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
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Last Edit: 26 Feb 2017 02:50 by goeco. Reason: add image rather than just link to it.

Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 27 Jan 2017 13:56 #20257

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    jankn
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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?
Jan Knappe
Doctoral Researcher on modeling of soil biomass in on-site domestic wastewater treatment installations
University of Limerick and Trinity College Dublin
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Fwd: DEWATS in Afghanistan doesn't work? 27 Jan 2017 22:12 #20260

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    sreuter
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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
BORDA

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Last Edit: 28 Jan 2017 00:13 by muench.
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Re: Fwd: DEWATS in Afghanistan doesn't work? 28 Jan 2017 00:29 #20261

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I am in "learning mode" on the kind of technology being discussed here, and very much appreciate clear questions and clear answers. Very helpful. I'll second that on the value of the Forum.
Diane M. Kellogg
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 28 Jan 2017 06:31 #20266

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Dear Jan

Nice to see you here too, currently I work with ministry of Urban Development and housing. As you know we implemented DEWATS in many of our project but as I mentioned in cold season we have some problem with it.

I am appreciated if you have comment in this regards.

Best

Qasem
Last Edit: 29 Jan 2017 09:47 by qasem120.

Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 28 Jan 2017 09:15 #20268

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We're talking about a capacity issue resulting from lower microbial action because of lower temperatures (think refrigerator). It appears that Kabul occasionally gets to as low as minus 15 degrees C, but only overnight. Assuming winter daytime temperatures are considerably higher than overnight temperatures, there would still be many winter days that reach suitable temperatures for biological activity to take place.

Overnight and when temperatures get really low, recirculation is not only impossible, but it would also not achieve anything because there is no biological activity. The idea with using solar panels is that they would activate pumps when these are needed, during the daytime when temperatures are well above freezing. I'm just thinking that by converting the existing baffled reactor infrastructure from anaerobic to aerobic to improve its efficiency, the capacity issue could be overcome. Pumps would be required for a recirculation retrofit because it appears that the existing Kabul systems are designed to receive sewage influent below ground level. A primary vermidigester retrofit that intercepts solids before they enter the DEWATS would need to be above the inlet, but below the sewerage outlet to be passive (requiring no pump). That is, gravity operated vermifilters require no power, but fall is necessary (see below).


Figure 3: Passive Vermifilter/Biodigester
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Re: Reply: Best decentralized treatment solution for a city without a centralized sewage system? 30 Jan 2017 11:43 #20279

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Dear Dean,

I personnally like vermi-composting very much and I have seen several projects in which it worked very well including in mountain areas where it snows in winter in France. The worms would die in the winter(composting in stand-by) and the eggs would hatch in the spring hence starting again the composting process.

What I would like to know is the following: do you have any case studies of your system being functional in an environment similar to Kabul, which I understand is characterised by very cold winters, very hot summer and little water?

In the cases I mentioned above the spring, summer and winter had warm temperatures, but as you know above 25°C, the worms' activity is decreasing. Also you seem to say that the biological activity can take place during the day in winter but how do you keep worms alive, when there are freezing temperature?

Is your system designed for individual sanitation or centralised sanitation?

thanks! Cécile
Cécile Laborderie
MAKATI Environnement

Re: Reply: Best decentralized treatment solution for a city without a centralized sewage system? 30 Jan 2017 13:36 #20280

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Afghanistan needs a long journey to cover in terms of wastewater treatment as up to now less than 5% of urban population have access to centralized/decentralized wastewater treatment system. DEWATS has contributed alot in last few years since this system has been introduced due to its lower technological and operational requirements.

Taking into consideration recent energy crisis, technological limitations and technical capacities in urban sector, DEWATS system has played substantial role in treating urban wastewater in Afghanistan, however modifications in the system design are subjected to weather and geographic variables, if energy availability permits we can think of using kind of aeration tools. However still in the prevailing energy crisis, adaptation to cold climates are considered in the design of DEWATS systems recently by increasing the size of system and installing planted gravel filters/ constructed wetlands at the end of the system.

Should there be a more resilient system available to withstand cold climates in the context of Afghanistan, sharing the information would be highly appreciated.
Riaz Darmal
Director of Water Supply, Sewerage and Environmental Affairs
Ministry of Urban Development and Housing
Kabul, Afghanistan
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 30 Jan 2017 23:53 #20287

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Dear All,

very interesting discussion here.
In general, we can say that the efficiency of the anaerobic treatment modules (septic tanks, ABR, AF, etc) goes down...and Marjin is correct and that system have to be designed "bigger" to cope with the dormant microorganisms during the winter. However, steel and concrete is expensive in Kabul, ... And as Elizabeth mentioned, also the design should consider that Kabul can be very cold of course. It will be a good idea to conduct a workshop in Kabul and hint on the importance of the design parameters / adjusted design for Afghanistan to cope with the cold climate...I can imagine that the DEWATS engineers from MUDA and AUWSSC (utility), will highly appreciate this, as BORDA has developed certain designs and made a couple of lessons learnt on how to improve the efficiency of DEWATS during cold winter and what kind of technical adjustments wont work...For example insulating the anaerobic treatments modules (e.g. with thicker concreting on top) is not so beneficial since you also insulate the system against warming sun rays during the summer time...

Actually in the past we only promoted anaerobic treatment modules, but people show ownership for DEWATS in Kabul and now more and more horizontal gravel filters are being implemented in urban areas even; mostly for public buildings (hospitals, ministries, Kabul University etc.). Planted / Horizontal gravel filter do work very well also under very cold condition...maintenance requirement is definitely higher but doable. I will request the BORDA team in Kabul to do some samples on our office system using anaerobic modules + planted gravel filter. We will share the results.

Coming back to the topic: "Best decentralized treatment solution for a city without a centralized sewag system" - I hope that the upcoming Kabul Sanitation Masterplan, financed by KfW bank and AUWSSC will give us further answer on that! For the time being I would like to refer you to the presentation of GIZ (Younes Hassib) on the TAF framework, focussing on Kabul and DEWATS:
vimeo.com/191973607
sanitationupdates.wordpress.com/2016/11/...ater-and-sanitation/

To provide some feedback on goeco´s points on septage / sludge treatment:
Please have a look into the draft Shit Flow Diagramm for Kabul city
www.susana.org/_resources/documents/defa...612-7-1471005402.pdf

Situation is not good, shallow ground water in Kabul is already very polluted but the president of Afghanistan is aware of this issue and I hope that we can use the momentum of the upcoming FSM4 conference for Kabul...giz, BORDA, and the various ministries in Afghanistan are working this!

Goeco, you wrote: "Looks to me like the BORDA system could be very easily adapted into an aerobic recirculating digester"
answer: yes that is true, and this could happen at a later stage...but whether it makes sense to itensify / upgrade the anaerobic DEWATS module or to connect the DEWATS effluent to advanced centralized systems; which hopefully will be implemented in Kabul one day, is subject to further scientific studies developing an incremental sector development approach (KBL sanitation Masterplan).

Goeco, you wrote: "How well are the filters being maintained? The anaerobic filter units must be rather unpleasant to remove and clean.
answer: some are well maintained, some could be maintained better. The cleaning of filter materials is easier than you might think-> de-water the AF compartment. Pour water on top of filter materials and at the same time de-water from bottom via desludging pipe...no need to shovel out filter materials...

Many greetings,
Alex
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 31 Jan 2017 12:49 #20293

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Dear All,
To add to the current discussion on DEWATS in Afghanistan, today we did the wastewater testing on one of the DEWATS system located at BORDA office compound in Kabul.

The results of the WW testing from this system is as follows;

Table.jpg


The efficiency of the system is around 80.25%.

January is the coldest month in Afghanistan and as you can see in the attached picture from this DEWATS system, there was a snow in Kabul last week.

DEWATSPIC1.jpg


The Technical Datasheet for this project is available in the link below;

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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 01 Feb 2017 14:06 #20311

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    Bhaskar
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An aerobic system may work better.
We can produce all the oxygen required by growing Diatom Algae.
A few reports available on Internet about Diatoms growing beneath ice -

Arctic - www.windows2universe.org/earth/polar/arctic_marine_life.html

Antarctic - blogs.jcvi.org/tag/diatom/

Lake Erie - www.sciencedirect.com/science/article/pii/S0380133011002619

Diatoms grow better in cold water than in warm water.

We have a solution to grow Diatoms at a low cost and in a simple manner.
In covered tanks electric lights would have to be used.
Light requirement is about 1,000 watts LED per 1 Million Liters per day sewage.
Power consumption would be a fraction of the power consumption by conventional electric aerators.
Clean technology promoter.

I am working on a clean technology product to grow Diatom Algae in large waterways. Diatoms account for about 25% of all photosynthesis on Earth and hence are the best solution to consume CO2, N and P and oxygenate water and feed fish.

I am a Chartered Accountant but am now an entrepreneur focussed on clean technology.

Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 02 Feb 2017 04:24 #20316

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Thanks to the BORDA people for providing some detail.

Cecile, thanks for your questions. No I don't have examples of vermifilters operating in cold dry climates but am interested in possibilities. Dry isn't an issue because in this case we're dealing with wastewater. Also keep in mind that the inclusion of worms in a trickling filter aids in maintaining sufficient percolation... however microbial action and aeration occurs whether worms are present or not.

Looking at the temperature range in Kabul, it doesn't appear to be that extreme. I'd suggest insulating a vermifilter to not completely freeze inside would be very easily achieved. Also, you can't pump ice ...and I'm struggling to imagine that the wastewater volume inside an underground DEWATS would freeze solid in Kabul.

Also, one should keep in mind that it isn't the temperature of the air that is important, but the temperature of the wastewater, which is not subject to the same extremes as air temperature. This regulates the temperature of the biofilter medium and therefore biological activity. Is an insulated biofilter more reliable and efficient than a planted gravel filter that is exposed to the elements and therefore higher temperature extremes? Simple tests would provide the answer to that question. So is it sensible to delay testing until a later time, as Alex has suggested should happen "one day" as part of scientific studies for incremental development of the sector? No, I don't believe so. Testing is just simply the stakeholder trying out retrofits for a whole year on a couple of the problem units to see if they fix the capacity problem. Simply seeking some good advice on low cost options and getting on with the job. Rule of thumb: if the effluent still smells then you haven't fixed the problem, so move on and try something else. This is not rocket science.

Insulating the existing treatment modules with thicker concrete would certainly not be good advice. Ten centimetres of concrete has about as much insulative value as 2 cm of straw. Of course straw could also be removed when not required in the summer... as could a range of other cheap insulative materials.

Recirculating through trickling vermifilters is easily scaleable and I'm looking for any good reason why it shouldn't be tested as an upgrade for Kabul BORDA DEWATS that have flow exceeding their capacity. The planted gravel filter has shown some benefit in the BORDA head office example and offers some value as a low cost retrofit, also being part of the original BORDA design. Tests would certainly be essential in the short term to compare costs and benefits between alternatives. Planted gravel filters could also be installed in series if there is room.

What I'm struggling with is the concept of starting with the BORDA DEWATS on the pretense it is a standalone treatment unit, but later advocating connecting the outlet to a centralised system. Either the DEWATS does the job or it doesn't. Looking at the construction pics, this system certainly looks substantial in terms of labour and materials. The result is well over 8 cubic metres of tanks processing 2 cubic metres per day from 20 people, or 100 litres per day per person taking 4 days to process (a capacity maximum of 400 liters per person). This example is combined greywater/blackwater, including bathing, kitchen and toilet, so is not only flush toilets.

The effluent last October (Autumn, 20 degree wastewater temp) exiting the DEWATS and entering the plant filter had a COD (Chemical Oxygen Demand) of 150 mg/l, after removing 180 mg/l. I'd be interested in others thoughts, but to me I can't see how anybody would expect such a system to be a sustainable solution for developing countries. Although simple, which is good, It is just not sufficiently cost efficient for the job it does. To me the plant filter add-on comes across as a bit of an excuse for poor performance, but in itself is highly effective by removing nearly 100 mg/l COD.

Maybe the BORDA anaerobic system is good enough until something better comes along, but to produce an effluent quality good enough for food crops should be the aim for system providers, not good enough only for disposal to sewer. Keep in mind that this system produces sewage sludge and "partially" treated effluent, both of which remain a problem.

My recommendation for the DEWATS at the BORDA office in Kabul is to invest in a 120w solar panel
(available in Afghanistan for $209), start with a 20w fountain pump with a 2m head ($20), build a 1m3 above ground insulated tank and test out a vermifilter recirculating from AF to ABR entry, then monitor COD and publish their results to this forum. I'm sure BORDA can afford this within their R&D budget. Not only might the retrofit vastly improve the efficiency by converting to aerobic digestion, but also sludge from all stages could periodically be pumped into the vermifilter to be converted into humus. And I'm sure the solar panel could be set up out of reach or sight of passing rogues.

cheers
Dean
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Last Edit: 02 Feb 2017 04:36 by goeco.

Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 05 Feb 2017 16:16 #20354

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Dear Dean,

a quick one:
the weather in Kabul can be extreme...the next days night temp is dropping to -10° C. Many international flight canceled over the past days and the government accounced public holiday to day due to the snow chaos. The last years avalanches destroyed power cables resulting in power outages...an improved septic tank with a planted gravel filter is a robust system and a profen technology for the context in AFG. Keep in mind that DEWATS does not require electricity, has no moving parts and operation requirement is extremely low and affordable. One might say DEWATS is so old school...but often you can travel further using a VW-beetle instead of an Ferrari, and you can still upgrade your beetle with a Porsche motor if you prefer...

In AFG we build systems with treatment capacities of 2 - 450 m³ ww per day...if the user is in favour, biogas usage is an option..please feel free to like our fb-page. web.facebook.com/Biogas-Consortium-Afgha...20668934631942/?_rdr

I am not yet convinced that trickling vermifilters are applicable for the Kabul context. Please provide design manuals, O&M guidelines, effluent values, costs, and real examples within an urban setting. How can the systems be integrated in highly dense urban settings? Can the system be used as parking lots? what are the operation requirements? OPEX? What sanitation service are required when you would scale-up? That you potentially avoid the septage / Fecal sludge problem is interesting though...but as we can see dissemination projects of composting toilets for schools in AFG, major problems might come along...

Every technology and approach has pros and cons...but current institutionalization of DEWATS in AFG speaks for itself. I again doubt that a trickling vermilter is the right choice for upgrading DEWATS...would be great if you could provide conceptual drawings how this could look like in practice, then we are more than happy to try it out. Please show us how this could be feasible. Aerated planted gravel filters, sludge recirculation + aeration for the anaerobic modules seem to be much more feasible and easier to implement.

And no, not only the air temperature is cold...the water is super cold during the winter. Groundwater temp. is relatively stable but in Kabul the water is mainly stored in mostly uninsulated overhead water tanks...to improve DEWATS efficiency one might want to look into tackling this problem. Of course you can also here install a solar heating device...but thats not really feasible.

Dont get the point of your rule of thumb...when you look at the picture above, you can see a cascade fountain...there is hardly any smell after the pgf and we also have a vortex. And even if you only apply anaerobic modules, there are so many ways to prevent "smelling" the treated wastewater..(dilution with grey/rain water, percolation, sub-surface drip irrigation, etc.)

If sludge from anaerobic DEWATS modules can be treated with for example larger scale trickling vermilters, then I would rather see this approach to tackle the sludge problem rather using it to upgrade or DEWATS. Do you have examples of treating stablized sludge from anaerobic digesters using trikcling vermifilters under colder climates?

Cheers,
Alex
Last Edit: 05 Feb 2017 16:26 by Miller.
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 06 Feb 2017 09:32 #20360

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Hi Alex,

I agree that simple is good, where possible. In this case, because my suggestion is for a retrofit rather than a new system, a small amount of electrical energy is required for modifying the existing system to an aerobic environment (in this case using recirculation).

My criticism of the BORDA anaerobic DEWATS is multiple-fold:
  • Septic sludge generation (disposal issues)
  • Large capacity required per user (cost)
  • Methane and nitrous oxide generation (if not utilised. If utilised, this might justify the capital investment in capacity)
  • Relatively poor treatment efficiency (overcapacity problem)
  • Poor level of treatment, requiring further tertiary treatment.

Unlike a VW Beetle which is a very effective transportation machine, a cynic might suggest that the BORDA DEWATS is really is only a sedimentation device... rather than a treatment system. More like a VW beetle without tyres.

Lets focus on design considerations for experimentally converting an anaerobic DEWATS into an aerobic vermifilter treatment plant. This doesn't require design manuals and guidelines, but simply the motivation to test options at a pilot scale. The concept behind vermifiltration (or trickling filters/biofilters) is very simple. A tank is constructed with an inlet at the top and an outlet at the bottom. It is filled with media. Wastewater flows in the top, through the media and out the bottom, in the process removing oxygen demand, suspended solids, and dissolved organics, while also aerating the wastewater. The design considerations are capacity and flow. A starting point for developing systems for Kabul conditions could be my suggestion for a 1 m3 capacity vermifilter and 20w fountain pump (i.e. high flow low head) for the BORDA demonstration unit. You have test results under the current configuration, so results could then be compared to determine the retrofit's effectiveness.

sludge recirculation + aeration for the anaerobic modules seem to be much more feasible and easier to implement.

Sludge recirculation + aeration continues with the status quo, that of scaling down centralised systems. The problem is economies of scale, i.e. cost per person. You'll also need a 200w aerator and 1000 watt panel for a plant the size of the BORDA demonstration unit. Then, how do you propose to implement sludge recirculation? Periodic sludge removal to vermifilter could use a portable sludge pump shared amongst 100's of DEWATS.

I have offered three simple designs for testing in Kabul, firstly one for onsite disposal of domestic blackwater. Flush and forget, safe subsurface disposal, with removal of humus every 5 years (figure 1). Then, if incorporating greywater and scaling up, aerobic treatment can be achieved with a simple design requiring no energy input and surface irrigation (figure 2). As a retrofit to the anaerobic DEWATS I have suggested that recirculation + aeration can be achieved with solar energy (figure 3). I'm still puzzled about the energy issue though... looking at the fountain above, is this (1) pump operated, or (2) is this fountain well below the outlet of the DEWATS? If (2), the cascade fountain could be replaced with a passive vermifilter for much higher level of treatment. If (1), the pump would be far more effectively used recirculating the wastewater through a vermifilter.

Don't get the point of your rule of thumb

Rule of thumb: if the effluent still smells then you haven't fixed the problem, so move on and try something else.

Because there has been so little information provided on what is wrong apart from "does not work properly", my assumption is that working capacity is exceeded in cooler months and the effluent is not treated adequately. Effluent that is not properly treated tends to smell sulphurous. If there is actually no problem then we're all wasting our time here. If the issue is only one of groundwater pollution then lets focus on what happens at the other end of the DEWATS:
Is all the treated effluent from BORDA DEWATS in Kabul disposed of to surface? If disposed to subsurface irrigation, is that because it is not treated sufficiently for surface disposal? Are all DEWATS outlets connected to some form of properly engineered soakage fields? Is sufficient land available or are some dewats connected to soak pits? Alex, I'm horrified that you would suggest that one can avoid smell by diluting with rain/greywater... what happens then to this water?

cheers
Dean
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Last Edit: 06 Feb 2017 09:38 by goeco.

Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 06 Feb 2017 13:17 #20367

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Dear Dean,

Please find my comments to your points above:

-Septic sludge generation (disposal issues)
Sludge generation of anaerobic systems is much lower then in aerobic ones. Please tell me more about the accumulation rates, handling of the vermifilter compost. As Kabul has no sewer system, people desludge their blocked soakpit to the storm water drains. DEWATS is not only a treatment device but also sort of a collection device, since anerobic treatment is not happening anymore at the storm water channels and blocking them, resulting in flooding of streets etc. Current sludge of bigger DEWATS is treated at the central wastewater treatment plant in Kabul. But an adequate service value chain is not fully set up in AFG...,work being done.
-Large capacity required per user (cost)
Yes, DEWATS on a household level is expensive, thats way rather bigger systems are implemented in Kabul tackling the big polluters. And once again please consider the life cycle costs, do not limit yourself on the initial investemnt of 1 single pilot intervention implemented at an office...
-Methane and nitrous oxide generation (if not utilised. If utilised, this might justify the capital investment in capacity)
Methane production is an issue, the use of biogas should be promoted
-Relatively poor treatment efficiency (overcapacity problem)
I disagree. You can reach very good treatment efficiencies. See the example above. Constraints are of course available space and budget. Please do not forget that even in Europe you will find examples where a primary wastewater treatment for remote communities for example is still in place

I gave you the contact of our R&D focal point. Please be in touch with him and provide conceptual design guidelines for him...your couple of lines are too vague. Once we have concrete implementation and operation guidelines we can go ahead and identify a suitable project location. We are also willing to make the investemnt that is needed.
As the DEWATS system at our office is working very well and is nicely integrated into our compound, I doubt the the colleagues will implement the vermifilter there... What filter material is required? is that locally available? Material of the tank? Any modifications needed? will the system be overground or underground? Looking forward to get things started and share the results, but proper guidance from your side to the team is crucial.

Regarding your other point,
You mentioned that DEWATS is only a sedimentation device - that is not correct. DEWATS has more treatment modules than only a septic tanks (amongs planted gravel filter, oxidation ponds etc.). Looking solely at the anaerobic modules, they can be considered as a solid retention device, yes.

Regarding the DEWATS effluent:
We have all kinds of disposal systems, infiltration fields, soak wells, french drains and of course using the water for irrigation purposes. And yes, we mix part of the rain water with our treated wastewater and use it for the irrigation of our vegetable garden, trees and grass fields of our office yard...

I assume the statement that was previously made "DEWATS does not work in winter times" was probably a bit excessive,...also no further deatails and info were provided here. So to sum it up: Yes, efficiency of anaerobic DEWATS modules goes down during cold climate, but the efficiency drop can partly be compensated through the use of planted gravel filters and one should consider current framework conditions of the context in Afghanistan (e.g. energy crises, sanitation sector still developing, limited capacities, civil war scenario and many more)

Cheers,
Alex

Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 09 Feb 2017 10:53 #20392

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Hi Alex,
thanks for your positive response. I sympathise with the situation in Afghanistan and I'm only too happy to share my ideas and experience in hope of making a difference.

At a domestic scale I have been practicing removal of sludge (sediment) from septic tank to vermifilter. The volume is reduced multiplefold (5 - 10 x) with the result being black humus that has a loamy texture with no smell. This can be handled and spread around as mulch under trees etc. You can use the same vermifilter for recirculation and sludge processing, so a useful reactor. Sludge processing should take about 2 months from addition to decomposition, depending on volume and temperature. A thicker layer will take longer to reduce. Do you have data on sludge production volumes for your units? The vermifilter should be wider if processing sludge and taller if processing wastewater only. This is because with increased surface area the layer of sludge will be thinner and so process faster, whereas with wastewater the retention time (i.e. contact with the media) is more important. Your design would trade these two off and most likely be a similar height as width. Multiple drippers/tricklers would distribute recirculating wastewater evenly over the surface of the media in the reactor.

I am not familiar with your construction materials and methods, so can only offer some design guidelines at this stage.

I'd estimate that conservative vermifilter capacity for recirculation would need to be 100 litres per person. I'd limit sludge addition to no more than 10cm depth of dewatered solids at one time.

The outlet at the bottom of the reactor must be above the inlet of the ABR, and connected to this. Thus if your DEWATS inlet is at ground level, the vermifilter would have to be over-ground.

The reactor does not need to be water sealed because it does not fill with water. There must be adequate ventilation in the reactor but in your case it would also need to be well insulated. Ideally there is an air cavity between the filtration medium and the wall of the reactor, to improve ventilation, along with air vents at the bottom and top. The top needs to be able to be removed to access and remove humus. I'm just not sure what construction materials you have access to but would be interested in providing feedback on your design ideas.

What kind of coarse organic materials are available ion Kabul? I imagine woodchips or tree bark would not be available as inexpensive filtration media?

Would be a remarkable to see decentralised systems transform Kabul by safeguarding groundwater quality, but also greening the city by using the nutrient rich wastewater and humus to grow crops and trees that would not otherwise survive in such a low rainfall environment.

cheers
Dean
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Last Edit: 09 Feb 2017 10:57 by goeco.

Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 17 Feb 2017 11:09 #20484

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Hi Everyone;

Just out of curiosity, why not consider using a decentralized solution with a centralized network and treatment plant. We have been building these in canada since 1999. here in India our first at a tribal village in Gujarat was commissioned in early 2016 and has been working perfectly since then. From the trail above, I suspect we solve most of the problems identified.

Have a look at our website www.clearford.com and if anyone wants additional information, do have a look at the attached documents - a project writeup and the latest test results. Water supply at the village is 70 LPCD.

Sanjay
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 17 Feb 2017 13:20 #20488

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Hi Sanjay

Nice project, especially the community-based approach. A few quick questions:

The Clearford system presented, how is it different from a normal solid-free sewer system with a septic tank (justifying the trademark)? The document even states that the single-chamber solid retention tank produces "significantly less sludge" than a regular (two-chamber) septic tank - how is that achieved?
What is the CAMUS SBT treatment exactly (a wetland?), and what are those enzymes it needs to run?
The document mentions potential flooding in the monsoon season. How did you solve this with the retention tank - it seems only to rise up to ground level?
Did you reach ODF status in the village in the end?

And finally, how do you see scalability in a dense urban context as Kabul and how would you address the challenges discussed in this thread (cold winter, sludge disposal, GHG emissions, costs, space requirements) especially, when talking about more than individual household/toilet level?

Cheers
/Jan
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan) 23 Feb 2017 10:35 #20582

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The opportunity I see is in greening Kabul productively, using water originally pumped from under the ground, adding nutrients to it from human effluent, then actually using it productively, either for irrigating amenity plantings ...or better productive tree crops ...or even better food crops. If this could be done safely and at low cost right down to the household scale then why centralise? The only motivation for putting pipes in the ground would be cost saving, but networks of pipes are costly. The BORDA people have done okay with reducing costs in their decentralised system, but in my view this could be so easily improved, further reducing installation costs AND improving the effluent quality to be able to safely discharge to the soil surface for irrigation purposes. Currently the system only appears to achieve water quality suitable for subsurface discharge.

Unfortunately a paradigm shift is required, which tends to hold up innovation. My favourite quote: "Paradigms fall slowly, from the weight of repeated failure". Vermifiltration offers high levels of treatment and at low cost... win win.

The water resource is in short supply. The wastewater needs to be properly disposed of so it doesn't contaminate the water table, something very easily achieved in such a low rainfall area using surface irrigation, turning a problem into a resource. However, BOD and suspended solids need to be reduced to do this safely. Plant filters are one way. Vermifilters are another.

Jan, CAMUS looks like the Vision Earthcare brand of Soil Biotechnology (SBT) bioreactors that use vermifiltration and plants to purify primary treated wastewater.

Basically a proprietary culture of soil, earthworms, bacteria and special additives. Starts with a septic tank, then to the bioreactor, with rubble in the bottom as drainage layer, then proprietary rock material, special additives and soil as the filter layers. Plants are grown over the top of the SBT beds on soil bunds and wastewater is trickled on top.

There is nothing proprietary about the SBT apart from specific materials that are used, such as minerals and bacterial cultures. Check out their patent,
US Patent No: 6890438 " Process for treatment of organic wastes"
www.google.com/patents/US6890438

Interesting that on their facebook page, the company marketing these CAMUS SBT's, Vision Earthcare, are trying to monopolise their method of vermifiltration with their "patented Soil Bio Technology and Vermifiltration concept." They claim that "Vermifiltration looks like an unauthorized implementation of Soil Bio Technology (SBT) / Constructed Soil Filter (CSF) which has been developed at IIT Bombay by Prof H.S Shankar's group at Chemical Engineering IIT Bombay."

From what I can make out, what they have patented appears to only be very specific, their proprietary bacterial culture and minerals. They use rock powder (novel) and soil media (not novel). They make a special bacterial culture (novel). They use earthworms (not novel) and plants (not novel). They use trademarks and acronyms and proprietary names (novel). Seen it all before.

cheers
Dean
Dean Satchell, M For. Sc.
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Last Edit: 25 Feb 2017 20:25 by goeco.
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