Appropriate Septic tank Cleaning (emptying) Frequency

  • aasimmansuri
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Re: Appropriate Septic tank Cleaning Frequency

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Hi All,

Thank you all for giving your inputs to this topic...

My concern for oversized septic tank is that, as more and more sludge gets deposited in the septic tank due to long cleaning frequency intervals around 5 -7 years, doesn't the treatment process in septic tank get affected ?? because some of the cases show that the BOD levels of the effluent coming out of septic tanks is high, almost as if there is no treatment that is taking place in septic tanks ?

@Chrisully: The situation has not changed in many cities of india, the grey water and the black water in most of the non - sewered cities flows into the septic tanks and the effluent from septic tanks either flows into the soak pit or the open/closed drains on the road side.

@Frapoberlin: Please find attached some codes that we have for India on Septic tanks. We also have a code for Pre cast septic tanks installation, but i don't have the soft copy if i find one i will share it in the group. The Vietnam case study is good, it would be good if you could share more material on this.

Thank you all once again.

Regards,
Aasim

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Aasim Mansuri
Senior Research Associate,
Center for Water and Sanitation
CEPT University, Ahmedabad-380009, Gujarat, India
M: +91 98 98 324874 | O: +91 79 26302470

This email address is being protected from spambots. You need JavaScript enabled to view it. | www.pas.org.in
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  • Marijn Zandee
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Re: Appropriate Septic tank Cleaning Frequency

Dear Aasim,

To the best of my understanding, the fact that the septic tank is bigger then prescribed in codes should not stop it from functioning.

If you measure very high BOD in the effluent the following comes to mind:

1.) Despite the tank being larger than the codes, the level of solids has actually reached the point where the retention time is too small. (Tank is full).

2.) People use very aggressive cleaning agents, which affect the bacterial processes.

Have you opened any of the tanks that have high BOD effluent? If not, that would be a good first step to check if there is a scum (foam) layer indicating a working process and to check solid levels.

If you have opened some tanks already, please share your findings.

Kind regards

Marijn

Marijn Zandee

Kathmandu, Nepal

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  • mwaniki
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Re: Septic tank diagram

Dear All

Could someone kindly remind me where I could find a simple septic tank diagram accompanied by notes for construction by a semi-urban community possibly with a consideration of a good suction system to flush out the faecal sludge.

Kind regards

S.Mwaniki
Publisher - Africa Water, Sanitation & Hygiene

Am the publisher of the Africa Water,Sanitation & Hygiene and the C.E.O. of Transworld Publishers Ltd.,Nairobi-Kenya.
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  • jonpar
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Re: septage management in Haiphong

Florian - can you give more information about septage management in Haiphong. I am particularly interested in the mobile transfer stations and the "free" septic tank cleaning service every 5 years (with costs being covered by the waste water tariff). Looking forward to hearing more about this. best regards, Jonathan

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  • cecile
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Re: Appropriate Septic tank Cleaning Frequency

christoph wrote: Hello,
situations where no grey water goes to the septic tank help a lot (just practical observation by operating a fecal sludge truck, no scientific investigation)


@ Christoph : what could be the reason for this, Christoph ?
I would tend to think that on the contrary, if there is no grey water in the septic tank then the fluid inside the septic tank would be quite viscous and too thick to pump out. I have heard (but I haven't seen in directly) that in that case the desludging operators have to introduce (pressurised) water to facilitate the suction.

@Jonpar : the same system exists in Manila in the Philippines. I attached an extract of research and presentation (dates back to 2008)

Some time ago we had a discussion on the forum ( forum.susana.org/forum/categories/53-fae...em?limit=12&start=12 )about Effective Microorganisms in the form of additives / powders sold on the market and their efficiency on decreasing sludge formation at the bottom of the tanks and therefore spacing the clearing frequency. I talked about this with a decentralised sanitation technician who said he observed a very good effectiveness of the Eparcyl additive : one mechanical action because the powder is made of small solids, sort of small balls which are suspended in the liquid area of the sludge (media to fix bacteria) and contains biological agents which enhance the bacterial activity (yogourt type bacteria). Without being a magical treatment it seems that it does have a positive impact on the clearing frequency.

Cheers,

Cecile

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MAKATI Environnement

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  • jonpar
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Re: Appropriate Septic tank Cleaning Frequency

many thanks Cecile. I didn't know they had the same arrangement in Manila. Can anyone provide me with more information about the transfer stations referred to in Florian's email ? best regards, Jonathan

Dr. Jonathan Parkinson
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  • aasimmansuri
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Re: Appropriate Septic tank Cleaning Frequency

Hi Jonathan,

Following is a link to the page from where you may find more details on the Haiphong septage Management.

www.waterlinks.org/partnerships/iwk-haiphong-septage-management

Hope its useful.

Regards,
Aasim

Aasim Mansuri
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Center for Water and Sanitation
CEPT University, Ahmedabad-380009, Gujarat, India
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  • pkjha
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Re: Appropriate Septic tank Cleaning Frequency

Dear Aasim

In an over sized septic tank -cleaned after 5-10 years, sludge at bottom of the tank becomes more compact. In such case tank can't be emptied through sludge pump.It requires manual labour to clean the bottom of the tank. In some cases such sludge is disintegrated applying forced water. It is a cumbersome process and there is unnecessary loss of water.Cost of such septic tank is obviously quite high. It discourages other people of the community to adopt this technology. In case of over size tanks, quality of effluent- in term of BOD, COD, suspended solids would be better in early months due to high retention time of the tank. However, at later stage -when the tanks are filled, quality of effluent would decrease considerably.
regards
Pawan

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  • vdamato
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Re: Appropriate Septic tank Cleaning Frequency

Hey all -

Check out this guidance document on septic tank performance that I did for the Water Environment Research Foundation a few years back: Factors Affecting the Performance of Primary Treatment in Decentralized Wastewater Systems . The Research Digest is the most detailed product. See pages 2 and 17, in particular.

Your observation of longer desludging intervals for relatively larger tanks is supported by published research. Theoretically, the longer sludge age should better facilitate methanogenesis and likewise, more complete treatment of organic cabon. Additionally, as has been stated, the rate of sludge accumulation will be lower since you will have more efficient digestion of the settled sludge. I personally support "oversizing" (relative to rule-of-thumb standards) septic tanks. I don't see any particular drawback and several potential benefits, although those benefits are not fully documented in the literature.

Vic

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  • Florian
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Re: septage management in Haiphong

jonpar wrote: Florian - can you give more information about septage management in Haiphong. I am particularly interested in the mobile transfer stations and the "free" septic tank cleaning service every 5 years (with costs being covered by the waste water tariff). Looking forward to hearing more about this. best regards, Jonathan


Hi Jonathan,
sorry for being late, I missed your post as I was away for a while (incidently in Vietnam, but for holidays this time, not checking on septic tanks ;) )

My own experience with Hai Phong is a bit outdated and limited. In 2001 I did a 1 day visit there. It is documented briefly in this document: www.eawag.ch/forschung/sandec/publikatio...m/dl/FSM_Vietnam.pdf

Here a copy of the respective paragraph:
"Haiphong (pop. 400,000)
The Sewer and Drainage Company is responsible for septage collection. Collection is car-
ried out with vacuum tankers and small vacuum tugs for areas difficult to access, used together with intermediate-storage-tanks mounted on a hook-lift truck. The mini-vacuum-tugs were developed by the company in collaboration with a local manufacturer. They have a capacity of 350 L and cost around 4000 $. The combination of large and small equipment has proven successful and almost 100% of the houses can be covered. The septage is disposed on the landfill, which is not perceived as satisfactory solution by the Finnish Water Supply and Sanitation Project. A future World Bank project will contain a component for septage treatment, drying beds were mentioned as possible treatment option"

The "Landscape Analysis and Business Model Assessment in Fecal Sludge Management: Extraction and Transportation Models in Vietnam - Final report" financed by BMGF and done by the Hanoi University of Civil Engineering has a detailed description of sludge management in Hai Phong, probably answering most of your questions. If you need more info, you'll need to ask the author, Prof. Nguyet Viet Anh. He's the one to ask for anything sludge or sanitation in Vietnam.

Other institutions to ask would be the GIZ programme on wastewater GIZ programme on wastewater (they have done quite some work on decentralised urban sanitation and septic tanks in northern Vietnam) or Sandec (they currently have a PhD student working on fecal sludge in Vietnam, perhaps they have more recent info on Hai Phong).

Best wishes, Florian


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  • muench
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Re: Appropriate Septic tank Cleaning (emptying) Frequency

Dear Aasim,

I just wanted to go back to what you said at the beginning of this thread three years ago:

In India there are codes and manuals which have standardized size and cleaning frequency of septic tank.These suggest a maximum interval of 2 years for cleaning of septic tanks and related sizes linked to loads.


Do these codes actually mandate that the septic tank is emptied every two years (I would call it "emptying", not "cleaning"), or is it more like a general recommendation?

In your work with faecal sludge management systems in the last few years as part of your PAS (Performance assessment system) project (see here on the forum: forum.susana.org/forum/categories/183-mo...niversity-india#9784 ), have you come across any cities in India that are doing scheduled septic tank emptying programmes?

This is something that we recently discussed here on the forum under the theme of city-level financing and full cost recovery of urban sanitation:
forum.susana.org/forum/categories/192-th...ire-sanitation-chain

You, or anyone following this thread, might like to take a look at that new thread and react to some of the points raised there. Thanks.

By the way, faecal sludge transfer stations were also mentioned in this thread a year ago, and are now being discussed in another structured discussion here on the forum:
forum.susana.org/forum/categories/99-fae...ge-transfer-stations

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Elisabeth

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  • pkjha
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Re: Appropriate Septic tank Cleaning (emptying) Frequency

Dear Elisabeth

In India there is one Manual on Sewerage and Sewage Treatment, from CPHEEO, Ministry of Urban Development, Government of India. Its latest edition is of 2013. Chapter 9 of the Manual deals with on-site sanitation including Septic Tanks.
Size of septic tank and its emptying intervals is perhaps never followed as per the Manual, neither is it a mandate. In fact septic tanks are constructed by masons who never know the Manual and CPHEEO. Size of a septic tank is decided by the concerned masons and households depending on their affordability /economic status. Larger size of tank is considered better as its emptying interval is longer.
Emptying is carried out only when the tanks are completely filled and there is physically blockage of sewage from toilet Pan to tanks. Depending on the size of tanks, cleaning interval varies between 5-10 years or even more. At initial years there is treatment of sewage with better effluent quality due to longer retention time, but in subsequent years there is practically no treatment after the tanks are filled. Practically such septic tanks act as storage tanks.
Status of septic tanks linked with public/ community toilets is worse. In most of the cases, such tanks are of undersized, due to lack of space or fund or both. In this case also emptying is done only after there is back flow of sewage. Most of such toilets are maintained on pay and use basis by service providers/ contractors. They are rarely concerned with the treatment of sewage; they are more concerned with economic aspects. To follow the Manual to emptying the tanks ( in 1-2 years) will cost more and hence not interested.
Regards

Pawan

Pawan Jha
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Mahavir Enclave
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