Regular septic tanks vs Biodigester septic tanks

  • pkjha
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  • Working for over 30 years in the fields of sanitation, biogas from human wastes, septage management, waste water treatment in rural as well as urban areas in India and other developing countries.
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Re: Regular septic tanks vs Biodigester septic tanks

Dear Kevin and All
In my earlier posts on the topic, I raised similar queries and sought chemical and bacteriological analyses reports of treated effluent, but could not get. Earlier reports from the IIT (India Institute of Technology), Chennai on the performance of such toilets mentioned effluent quality not better than sewage. It was discussed at length. Treatment efficiency needs to be supported with design. As you pointed out there is no innovative designs to support better treatment.
best
Pawan

Pawan Jha
Chairman
Foundation for Environment and Sanitation
Mahavir Enclave
New Delhi 110045, India
Web: www.foundation4es.org
Linked: linkedin.com/in/drpkjha
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  • hoffma
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Re: Regular septic tanks vs Biodigester septic tanks

Hi James,

I had similar doubts when „self-cleaning-bio-digester“ for onsite treatment came to Latin American market, it was 10 years ago. Here, Biodigester are offered in different sizes, adapted to onsite RAW WASTEWATER treatment of 1 - 10 households (not only one latrine). Based on these experiences I can confirm that you are totally right with all your questions:

Biogas: as Tore already pointed out, this technology only applies to very small wastewater volumes with low methane building capacity. Without a doubt, that is exactly the same process as in Septic Tank (anaerobic or septic digestion) and important to note too, that Biogas production also depends on efficiency of the degradation process; higher efficiency means more liberation of methane.
Sludge: Raw wastewater treatment means solid separation and sludge retention, followed, in this case, by anaerobic degradation (sludge stabilization). So, “never need to exhaust” just means that solids were flushed out together with the effluent. It can be caused by hydraulic problems but also because it was never emptied.
Effluent: Septic Tanks remove 30-40% of BOD load; in this case higher enviromental temperatures have only a low influence, because in warm climates septic tanks are usually much smaller. In addition, the efficiency of anaerobic process is naturally limited; even more sophisticate anaerobic technologies will hardly remove more than 60-70% BOD (domestic wastewater). Therefore, there is necessarily still a relativly high concentration of organic matter in the effluent of EACH anaerobic treatment and it is important to note too, that these effluents have a blackish color and smell (H2S, NH3) or, if not, the treatment process probably did not work.

Pre-fabrication of onsite treatment tanks is an important market, but was happened in practice is, that the necessity to reduce costs, combined with poor regulation and lack of experience with the peculiarities of onsite sanitation often result in far too small treatment volumes. To compare: A Septic Tank for a household in cold climate (Germany) needs at least (4 pe) 6.000 L volume. In warm climate (Brasil) the maximum for a household (5 pe) is about 1.200 L and for the same situation the “bio-digester” is offered (Peru) with less than 600 L effective Volume. So, peak loads can hardly be absorbed. Totally agree with Pawan: efficiency needs design and biological treatment does not require the addition of effective bacteria, but the conditions that natural wastewater bacteria can work.

So, is a Septic-Tank-Digester still better than nothing? I would say that depends on the conditions, it may even be an appropriate solution if:
- if it fulfill common key design parameter for anaerobic treatment of raw domestic wastewater as: adequate sludge settling volume and hydraulic retention time and consideration of specific hydraulic load, peak load and climate condition.
- if onsite discharge (soil infiltration) of anaerobically treated effluent is possible without surface run off (risk of contact) and without risk for groundwater, walls etc. Otherwise, or in case of reuse, anaerobic effluent needs secondary treatment.
- if periodical emptying of sludge is possible, what means: appropriate access to sludge settling zone (preventing risk of contact) and “acceptable low risk” concerning finally disposal of treated sludge (after onsite drying or transport to central treatment).

Above all, of course, benefits depend on adequate training and awareness raising of user, especially if service is not available and user will be responsible for operation of the Septic-Tank-Digester.

I hope these experiences are helpful. Regards, Heike
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  • zigazie
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  • Holder of a Bsc in health promotion, Masters in public health- health promotion and Bill and Melinda Gates Foundation Scholar studying Msc in sanitation at IHE Delft Netherlands till April 2019
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Re: Regular septic tanks vs Biodigester septic tanks

Dear Dr Ashok

Thank you for your information on bio latrines. I am also interested in getting the designs you have been using. I am however keen to learn more about the quality of the effluent which you said goes into the drains. How safe is the effluent. Yes you mentioned that no smell no mosquitoes but what about the pathogens and BOD. I will be happy to hear from you as an expert because i have seen that most systems e.g in Bangladesh they also discharge the effluent into the drains straight from the septic tanks.

Ziggy Kugedera is a Holder of a Bsc in health pr4omotion, Masters in public health- health promotion and Bill and Melinda Gates Foundation Scholar studying Msc in sanitation at IHE Delft Netherlands till April 2019. Have 14 years experience in SBC, WASH and Public Health
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  • AjitSeshadri
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  • Marine Chief Engineer by profession (1971- present) and at present Senior Faculty in Marine Engg. Deptt. Vels University, Chennai, India. Also proficient in giving Environmental solutions, Prof. Ajit Seshadri, Environment Consultant located at Chennai, India
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Re: Regular septic tanks vs Biodigester septic tanks

Dear SuSanA Members.

We definitely need to innovate and apply natural principles to sustainable practices.

When an initiative starts to perform to communities, its like a life cycle of a new born baby.. to child.. then an adult.. etc.
Just like prudent parents, a child is nurtured and guided..a wwt digester plant too follows a path.. till it gets a sustained status.. then this plant's design is propagated with add-on features.

Only when the wastes are converted to resources eg re use water, compost, bio gas Etc, a confidence is built and communities start to experience a " feel good factor ".

We can propagate role models - growing elephant grass, harvesting them for uses viz. feed for cattle, poultry, fish feed Etc. for commercial consideration..
All the above done on compliance of standards and rules Etc..

Local jargon to term some bio digesters on urban drains as " gutter gas plants " has been there for a long time.. But all these initiatives add values to communities well - living..

Well wishes..

Prof. Ajit Seshadri, Senior Faculty in Marine Engg. Deptt. Vels University, and
Environment Consultant (Water shed Mngmnt, WWT, WASH, others) Chennai, India
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  • favortecwastewatersolutions
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Re: Regular septic tanks vs Biodigester septic tanks

if you are searching for a biodigester in kenya, you have to the right place as am an installer from kenya you can view our website on www.tonito.co.ke
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  • AjitSeshadri
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  • Marine Chief Engineer by profession (1971- present) and at present Senior Faculty in Marine Engg. Deptt. Vels University, Chennai, India. Also proficient in giving Environmental solutions, Prof. Ajit Seshadri, Environment Consultant located at Chennai, India
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Re: Regular septic tanks vs Biodigester septic tanks

Dear SuSanA Members.

Wherever we can we should use Biogas from Septic tanks for Energy and spent slurry for usage as compost

It is a problem if effluent is more diluted and in that case, can be used for secondary water for irrigation after remedying.

When it is gainfully used by and for communities, the systems are maintained and eventually sustained well.

SDGs and Climate change impacts are also addressed.

Well wishes.

Prof Ajit Seshadri.

Prof. Ajit Seshadri, Senior Faculty in Marine Engg. Deptt. Vels University, and
Environment Consultant (Water shed Mngmnt, WWT, WASH, others) Chennai, India
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  • Gituku
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Re: Regular septic tanks vs Biodigester septic tanks

Dear Dr.Ashok,
My name is Wambui from Kenya.
Would like to request you send to me the design for a septic tank biodigestor,and the size's Based on the capacity.
Currently im doing the dung biogas digesters.
Regards,
Wambui.
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  • AjitSeshadri
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  • Marine Chief Engineer by profession (1971- present) and at present Senior Faculty in Marine Engg. Deptt. Vels University, Chennai, India. Also proficient in giving Environmental solutions, Prof. Ajit Seshadri, Environment Consultant located at Chennai, India
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Re: Regular septic tanks vs Biodigester septic tanks

Dear Wambui,
I had seen your email requesting for a design for a septic tank/ bio digestor, and the size's Based on the capacity and for cow-dung based biogas digester or plant- BGP.
I have come across an Indian design by name- Deenbandhu Bio-gas Digestor done in 60s by AFPRO, Delhi, was considered well-proven. This model is fixed dome type, and another one is Floating dome type BGP. I attach a relevant design manual for same, you can easily calculate the appropriate design, based on daily feed x time 50days, in cbm m3 .
Pl feel free to be in touch with the concerned as given below: PIC : Mr. Kiran Kumar K- Secretary, SKG Sangha, Email ID: This email address is being protected from spambots. You need JavaScript enabled to view it. , www.skgsangha.org .
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You would note that the construction calls for intricate cement- masonary work done on red-bricks, which can be easily done by a competent mason.
With well wishes,

Prof. Ajit Seshadri, Senior Faculty in Marine Engg. Deptt. Vels University, and
Environment Consultant (Water shed Mngmnt, WWT, WASH, others) Chennai, India

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  • Ashok
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Re: Regular septic tanks vs Biodigester septic tanks

Dear Mr Wambui.
I am attaching a schematic drawing for the prefabricated bio digestor based toilet.
Another attachment is for the installation and usage of the same.
Please note that ir requires very little water as compared to normal flushing.
I have made more than 500 toilets for Indian Railways (a central government organisation) in 1994 and all of them are working fine to the entire satisfaction of the users.
Recently, I am been forced to make twin leach pit toilets (about 800)and water table being high, the users are not happy with it.
Please feel free if you need any more information.
with best regards,
Ashok Kumar Jain Ph D

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  • Gituku
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Re: Regular septic tanks vs Biodigester septic tanks

Dear Ashok,

Thanks so much for the response.
I have received the bio toilet literature and the drawing details.
If you have drawings for the urban septic bio digester,where we have black water(human waste) and grey water(kitchen and bathroom waste) i would request you share .
Kind Regards,

Wambui
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  • Ashok
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Re: Regular septic tanks vs Biodigester septic tanks

Dear Mr Wambui,
As far as my knowledge and understanding goes, there is nothing in Kitchen and Bath room waste water to digest.

Kitchen waste can be composted
Bath room water can be allowed in the open drain.
There are no harmful bacteria or pathogens in either of the two.
With best regards,
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