More compact DEWATS technology?

  • Marijn Zandee
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More compact DEWATS technology?

Dear all,

I was recently asked if a decentralized waste water treatment system could be installed at a hospital here in Kathmandu. There are some examples of DEWATS systems in the area, but they all rely on wetlands for secondary treatment. These wetland obviously take up a lot of space.

The issue is that we are looking at a building inside the city, which is very densely built-up. We could probably fit an ABR (with or without methane capture)under a parking lot or by sacrificing some basement space. But in the context here, the system would only make sense if we can produce an effluent that can be safely infiltrated into the soil (or disposed into the river), for which secondary treatment will be required.

My question, is there a simple, reliable secondary treatment option which requires very little space that I am overlooking?

Marijn Zandee

Kathmandu, Nepal

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  • Frapoberlin
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Re: More compact DEWATS technology?

Dear Marijn,

good question and I am curious to hear the answers.
In my view, "simple" and "little space requirements" are a contradiction in terms.

I have never heard of a second treatment step after an DEWATS ABR other then constructed wetland or (aerated) pond.

Soil infiltration might be an option, but usually the effluent quality from ABRs is not good enough.

There is absolutely no space for a nice reed bed around? I have seen solutions being part of the landscaping in a hospital area, along the fences and walls.
Regards
Frank

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  • JKMakowka
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Re: More compact DEWATS technology?

Especially since we are talking about a hospital (e.g. increased effluent safety requirements), the only solution I can think of would be a (relatively expensive) MBR: en.wikipedia.org/wiki/Membrane_bioreactor

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  • AquaVerde
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Re: More compact DEWATS technology?

Dear Marijn,

To have a much smaller footprint for the second treatment stage after ABR, you may "take out" the robust option, low-tech aerobic bio-film systems like CW's, who often do not have any power consumption.

You may go for other aerobic bio-film systems in compartments in the underground with artificial aeration (it needs external power for aeration to function proper, even if salesman claim the opposite, e.g. www.clearfox.info/english/products-8pe-CFnature.php )
this example is for domestic sewage only

or go for more high-tech systems like membrane technologies as Julius already mentioned, which need permanent power connection and a higher level of O&M as you know. Beside CWs, as fare I know only the high-tech plants will reach the right pathogenic level for hospitals.

So you have to compare the possible advantages of less space requirements with possible disadvantages of high-tech (less robust) very carefully.

Alternatively, how about pumping or draining the relatively "clean" effluent to a possible area with enough space for CW's?

If no alternatives available, unfortunately you have to go for the high-tech stuff. But maybe all is to expensive and not reliable enough and you may opt/suggest for relocation of hospital...

Just for a ponder, a good trail example of roof-CW by German CW-Engineer Mr. Blumberg: www.blumberg-engineers.com/PDF/Wetland_roofs.pdf
Maybe good "enough" for greywater treatment, but for hospital ABR effluent I would hesitate.

Good luck
Detlef

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  • christoph
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Re: More compact DEWATS technology?

Dear Marijn,
as you asked for simple secondary treatment solutions, which might be possible to be implanted under a parking lot, the only solution which comes into my mind are sandfilter trenches (Sandfiltergraben in german)published here for instance , the picture below gives an idea.

It is not a solution for large volumes and you should be sure tha you are able to have access to be able to clean out the sand...just in case of clogging due to overload!

The best is to guarantee pulse loading to those trenches (there are some simple siphons you can build for about 10 US), but still I would do a chlorination in the end with Hospital wastewater.

For larger volumes (as typical in a hospital) I think you can not avoid a more technical approach. I would go for SBR ... but that is another story - not low tech.

Yours Christoph
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  • Freya
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Re: More compact DEWATS technology?

Hi Marijn,
As you know I worked with local NGO ENPHO assessing DEWATS in Kathmandu in 2010. I agree it’s a difficult issue with tight space and uncertain power availability. However the systems at Dhulikhel and Susma Koirala hospitals in the Kathmandu Valley were working well enough. It would be worth testing the inflow/outflow from the ABR at Dhulikhel Hospital to assess the current treatment performance.

I can’t think of any specific solutions at this moment, but some suggestions from the other systems:
- I would not recommend Biogas since it requires a large area for limited treatment, which ABRs/AF could better provide.
- Disposal of medical waste could kill the bacteria. Parallel/batch systems could be beneficial, as well as waste management education. Rags were also an issue and blocked inlet screens regularly.
- Rainwater infiltration was high in the other hospitals, to maximise treatment improving the separation of streams would be important. (Testing at Dhulikhel in 2011 was after heavy rains and the results were obviously impacted by this)

Maybe contact the team at ENPHO for an update on the operation of the other hospitals or let me know if you want any background information.

Regards,
Freya Mills
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  • Marijn Zandee
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Re: More compact DEWATS technology?

Dear all,

Thanks for your inputs, we are not anywhere close to an actual project and I just wanted to double check that there is no "simple" solution. If this gets more serious I will pick up the question again.

One issue here with DEWATS in the Kathmandu valley is that land prices have sky-rocketed in the last 10 years. Making it much harder to use low-tech space intensive solutions. At the same time, apart from real-estate prices the economy has not grown very much. So we have a situation in which land is expensive, power most of the winter only available for 6-8 hours per day and also very few capable firms to run more complicated technology. What to do ? :(

@ Christoph, thanks these may be a solution in rural health posts, which a friend of mine is looking at.

@Freya, How are you? Yes I remember the days at ENPHO, if this ever gets serious I will definitely contact them.
There is some very interesting and cool stuff going on in hospital waste management in Nepal at the moment. My question was in relation to trying to include waste water treatment into hospital waste management systems; which look like they are moving beyond the pioneering stage.

Regards

Marijn

Marijn Zandee

Kathmandu, Nepal

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  • JKMakowka
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Re: More compact DEWATS technology?

Was looking for constructed wetland variations that avoid having to buy large quantities of sand and came across this:
www.wastewatertreatment.co.in/pdf/Treatm...cted-soil-filter.pdf
(laterite is the common red base-layer soil found in tropical countries, called murram here in East Africa).

Due to the deeper depth of the filter-bed it might have a higher pathogen removal per surface area, otherwise it is similar to a vertical flow constructed wetland.

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  • JKMakowka
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Re: More compact DEWATS technology?

Last quick idea:
A polyurethane trickling filter, or the advanced version of it e.g. a down-flow hanging sponge system might also be worth looking into.

Polyurethane filter foams can also be impregnated with silver-nitrate (a technology known from drinking water disinfection), which might be interesting for a final polishing step in the case of a hospital.

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  • ben
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Re: More compact DEWATS technology?

Dear all,

With GRET we worked in Cambodia on a kind of compacted DEWATS, I invite you to look at the concept note attached. The idea was to place an aerobic pond on top of the anaerobic one, followed by a drying bed. Economy of space, of material, gravity flow, etc ...
We constructed the structure but faced some trouble with the pit sludge removal business model. Budget for testing quality of effluent haven't been properly carried on either, which was a shame. If someone is interested I can send plans, photos and ask some feedback on how is the project going in Cambodia.

Wish you all a good day,

Ben

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  • AquaVerde
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Re: More compact DEWATS technology?

Dear Ben,

I am not involved in possible Nepal project, but I think your space saving solution is interesting, it reminded me of a stabled ABR by BORDA in Afghanistan, having the same space constrains at a moshe.

Maybe it is a good idea to share the mentioned details with susane-office to put it on the general susana-library.

All the Best
Detlef

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  • MichaelCarr
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Re: More compact DEWATS technology?

Hi Ben: I'd be interested in following your progress with DEWATS -
Mike - eco1solutins.com This email address is being protected from spambots. You need JavaScript enabled to view it.

cheers : )
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