Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

  • Hussain
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Dean,
Thanks for the feedback & information; appreciate it.

So you suggest treating blackwater and greywater combined, using simple vermifilter toilet. And the effluent better to be used for irrigation purposes but not for direct infiltration into the land (to protect the groundwater?).

Regarding more dispersal than concentrating WW, the good news is that almost whole houses in Kabul’s informal are big enough to disperse their wastewater (shallow wells are bit tricky here). Usually houses are bigger than 300 m2 and most of them have big yards where toilets located. And many of the yards have greenery as well.

@ Do you know any other good materials & links about vermifilter except what you already mentioned?

Thanks & Cheers,
Hussain

Hussain Etemadi,
PhD Student: HafenCity University, Hamburg (HCU)
Eawag - Swiss Federal Institute of Aquatic Science & Technology
skype: hussain.etemadi
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  • goeco
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Re: Best decentralized treatment solution for a city without a centralized sewage system? (Question about Kabul, Afghanistan)

Hi Hussain,

The simple vermifilter toilet (Figure 1, page 1) is designed for only blackwater because the soakage field is limited in size (to be easy to construct). For treating greywater and blackwater combined see Figure 3: Passive Vermifilter/Biodigester (page 2) and Figure 2: Aerobic recirculating biodigester (page 1). These systems produce effluent treated to a high level, which can be safely discharged to the soil surface. There is a much larger volume of water involved when you introduce greywater.

Subsurface soakage fields (usually used with septic tanks) are used when the effluent quality is not good enough to discharge to the surface. If properly designed they disperse the effluent and don't contaminate water tables, but where shortcuts are taken in sizing they may concentrate the wastewater and drain into water tables. I suppose the simple vermifilter toilet could be used instead of a septic tank for blackwater and greywater, provided adequate subsurface soakage fields were constructed to accommodate the greywater volume.

Surface discharge via drippers is much cheaper than subsurface soakage fields, so dispersal area can be larger... and the irrigation pipes can even be moved around. Much of the water is evaporated in a dry climate and what soaks into the soil doesn't get down into the water table. Bacteria are also more active in the surface layer of soil and nutrients such as nitrogen, phosphorous and potassium adsorb into the soil and feed the vegetation.

I have provided some further information on design in this topic .

The main issue with surface discharge is that the drippers need to be dosed, either passively (no electricity) or using a pump with float switch.


Dosing syphon

Use the passive system where you have enough slope to drain the wastewater through the system and then disperse the treated effluent without requiring pumps. Keep in mind that with a passive system dosing of the dripper lines is required. Otherwise the water discharges out of only the easiest drippers. Dosing is very easy though.

Active systems that have pumps would be necessary on flat land. The treated effluent gets pumped to the drippers using a pump with a float switch.


$100 submersible pump with float switch

However, there is a risk of overflow if power becomes unavailable or is available intermittently. If this is likely a solar panel, battery and DC pump would be the better option.

Here is a technical paper from Oxfam on construction of a vermidigester toilet.

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However, in my view you'd be better off just following my design.

There is very little good information available on vermifilters because it is a new technology and those who are commercialising it are protecting their designs and trying to gain commercial advantage... probably because they realise how groundbreaking it is. You really just need to construct a domestic prototype and use local resources to design the local version. It is a very simple system to design and build and I'm happy to help you with design ideas.

cheers
Dean

Dean Satchell, M For. Sc.
Go-Eco Sustainable Solutions
www.go-eco.co.nz
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