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

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

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

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

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.

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;



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.



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

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

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.

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

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

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

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.