Regular septic tanks vs Biodigester septic tanks


Page selection:
  • kevintayler
  • kevintayler's Avatar
  • I am a water and sanitation engineer, also interested in general urban housing issues. In recent years, I have worked on FSM for various organizations
  • Posts: 79
  • Karma: 11
  • Likes received: 46

Re: Regular septic tanks vs Biodigester septic tanks

I have looked at the drawings. As James says about the other design, I don't see anything about the Indian Railways design that makes this anything other than a 'interceptor' tank with liquid waste discharged to a drain. Regardless of tests, I am afraid that there is no way in which the effluent will be free of pathogens. The only treatment that will occur will be anaerobic and this will not be sufficient to remove pathogens. Rather crude versions of this technology are found all over Northern India and Pakistan. The tank acts as an interceptor for gross solids and sludge but will cease to hold sludge unless it is regularly desludged. (The size is smaller than that required for a simple septic tank so I would expect it to require desludging fairly regularly). This type of interceptor can provide some protection to the drain or sewer to which the effluent is discharged, reducing the likelihood that large solids will enter it and block it. However, the relatively small size means that retention will be fairly short and this presumably explains why the amount of gas generated is not very great.

Some research has been done into the use of additives to increase digestion rates in septic tanks but the general consensus seems to be that these additives have not been very effective. It would be interesting to get any feedback on this from those who know about the results of fieldwork
Kevin Tayler
Independent water and sanitation consultant
You need to login to reply
  • jamesoriga
  • jamesoriga's Avatar
    Topic Author
  • i am a Water & Sanitation Engineer who after many years fixings pipes and toilets, is now more a Public Policy Specialist focused on Fixing the Institutions and Systems that keeps the pipes and toilets fixed
  • Posts: 3
  • Likes received: 1

Re: Regular septic tanks vs Biodigester septic tanks

Hi there,
What makes your septic tanks "Biodigester"? All I can see is just a regular septic tank branded as biodigester, which is the common case with most of the suppliers I've seen on social media in Kenya.

James  Origa
BSc. Eng (JKUAT); MSc. Eng.(Nairobi); MPPM (Strathmore)
Water/Sanitation Engineer & Public Policy Analysis
Cell: +254 (0) 724 052620
Linkedin :  
You need to login to reply
  • favortecwastewatersolutions
  • Posts: 1
  • Likes received: 1

Re: Regular septic tanks vs Biodigester septic tanks

It is true there are many suppliers of biodigester setic tanks in kenya.They are many because sewer management in kenya has always been a major challege. Our company(TONITOTEC WASTE WATER PRODUCTS KENYA) does install biodigesters.
You cannot harvest methane gas from a biodigester septic because they have no gas holders. Kindly on the the structural design of a septic tank is different.
You need to login to reply
  • Tore
  • Tore's Avatar
  • worked in sanitation for most of my life. taught plumbing. have plumbing and builders license, certified inspector in all facets of construction, PhD in public administration & have taught construction management in university, traveled numerous countries, Interest UDDT and sanitation & clean water
  • Posts: 71
  • Karma: 2
  • Likes received: 24

Re: Regular septic tanks vs Biodigester septic tanks

In areas that periodically flood you will always have a problem with pollution from the septic leach field. You need a system that allows you to keep the toilet above the potential water level. A urine diverting dehydrating toilet would work or another system that periodically emptied. The question is if it is emptied where do they empty the effluent.
Sanitation & water consultant in developing countries
You need to login to reply
  • Genoveva
  • Posts: 1
  • Likes received: 0

Re: Regular septic tanks vs Biodigester septic tanks

Dear Ashok Kumar Jain,
we are a smal NGO. KINDEVA is going to build a school toilet in a small village in Irrawaddy Delta Myanmar. The village is located in a flooding area. I am interesting in design and technical data about septic tanks. Cold you provide me your design and your experience with the septic tanks. Regards Dr. S. Groß

This email address is being protected from spambots. You need JavaScript enabled to view it.
You need to login to reply
  • niketjha15
  • Posts: 1
  • Likes received: 0

Re: Reply: Regular septic tanks vs Biodigester septic tanks

Dear Sir,

The manual and presentation has no option of viewing or downloading..please share it in another format or may through other system so that the same can be accessed.


You need to login to reply
  • Ashok
  • Posts: 42
  • Karma: -1
  • Likes received: 16

Re: Regular septic tanks vs Biodigester septic tanks

Dear Mr Jha,
I have not got any lab tests done, as I did not feel any necessity. There is no foul smell, no mosquitos, flies etc. at the outlet of the effluent.
The desludging period mentioned in the manual is two years but in practice I learnt that desludging is very irregular, some times after 3 years. at times five years and so on. I do not live there and I worked as a contractor only to install these Bio Toilets as per there design except with change of material from Brick masonry to Ferrocement so that these becomes lighter and transportable. I have no idea as to the quantity of sludge and its disposal.
As far as the size of the digester is concerned, I have attached a few drawings from Northern Railway which are self explanatory.
For a family of five (average) the opinion of the Railway officers is that gas is so small that they do not bother to collect it and have provided a vent pipe to let the gases escape in the atmosphere.
The cost of the total BIO-latrine in 1993 was Rs 7500 each including the transportation from Lucknow to TUNDLA and all other stations up to Ghaziabad and installation.
At present. we are selling the same product in and around Lucknow at Rs 17000/= only.
The super structure in Ferrocement and twin leech pits in Bricks are being provided in Rs 12000/= only, if one insists on it, though we do not recommend it to safeguard the sob soil water and soil type.
Ashok Jain Ph D

This attachment is hidden for guests.
Please log in or register to see it.

This message has an attachment file.
Please log in or register to see it.

You need to login to reply
  • pkjha
  • pkjha's Avatar
  • 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.
  • Posts: 177
  • Karma: 11
  • Likes received: 72

Re: Regular septic tanks vs Biodigester septic tanks

Dear Ashok
I have a few queries
i. Did you analyse quality of effluent from biodigester, in terms of BOD, COD ,TS etc. from a recognised laboratory? Is there any such published report?
ii. As you mentioned, tank needs to desludge once in two years. How such sludge it taken out and where it is disposed?
iii. Retention time inside biodigester is of 30 days. Can you calculate and inform the size of the digester for a household toilet used by 5 persons per day.
iv. At such retention time there is better chance of production of methane ( Biogas). Is there any storage system of produced biogas for its use or produced biogas is allowed to escape through vent pipe in atmosphere.
v. What is the cost of the system ( costs of sub structure + superstructure)

Pawan Jha
Foundation for Environment and Sanitation
Mahavir Enclave
New Delhi 110045, India
You need to login to reply
  • Ashok
  • Posts: 42
  • Karma: -1
  • Likes received: 16

Re: Rural Sanitation Governance in India - any relevant studies or cases?

A Bio Digester

Dear Mr Kevinkuhn,
I read the message posted by you on Susan.
There is a design in Indian Railways called Bio Latrine. It consists of a Bio digester whose effluent can be directly discharged in open drain without any problem. The original design by Dr Y P Anand, then Chairman, Railway Board was in Brick masonry. Because of the scattered nature of work, I had the opportunity to install about 500 Bio latrines at almost all stations’ quarters for about 300 KM distance in the year 1993. These are functional with even today (2018). I am attaching a Power point presentation and a copy of Works manual for your ready reference.
A. A power point presentation

618 Bio-Latrines –

These are improved aqua privies used for sewage ranging from very small quantities to comparatively larger quantities. They need 1.5 to 2 litres/capita of water for flushing.

Standard drawings are available from RDSO.

The following points should be taken care of in bio-latrines.

1. No water tap should be provided in the water closet to prevent flooding of digesters, which will prevent efficient anaerobic action.
2. Excessive water should not be used in the water closet.
3. The pan in the bio-latrines should have a slope not less than 40 degrees with horizontal.
4. No foreign matter e.g. garbage, soap water etc. should be thrown into the water closet pan.
5. The digesters should be linked directly to the toilet with least possible inter distance.
6. The flow from the toilet to digesters is to be by gravity.
7. When combined digesters are used, the sewage will first get collected in a chamber attached to each water closet and then flow to a combined digester. The slope of the pipe lines from the collection chamber to the digester should not be flatter than 1 in 20 so as to allow for easy flow.
8. A water seal of 50mm above the crown level of the inlet pipe at the inner face of the digestion tank wall, shall always be
maintained in the digestion tank.
9. The plinth level of the latrines should be decided working backwards from the invert level of the outlet pipe of the digestion tank.
10. The sludge settled at the bottom of the digestion tank may be cleared once in two years.
11. Satisfactory working of the anaerobic digesters in the tank, is indicated
i) if the effluent is odourless
ii) if the effluent does not attract flies and mosquitoes; and
iii) if the pH value of the effluent is not less than 7.0.
12. Outlet drains should have proper slope and rounded corner.
13. Adequate ventilation should be provided in bio-latrines.
14. In case of public or community type of toilets, users are likely to throw rags, stones etc. into the toilets. In such cases an inspection chamber with 25-50mm spaced grating should be provided just before the entry of water into the digesters to arrest any such material.
15. A minimum retention of 30 days is required for anaerobic digestion, while a septic tank provides retention only for 2-7 days and hence the effluent from the septic tank must have its main treatment in a soak pit / filter while effluent from a digester can be discharged directly in a drain system.

Note: The people sitting on the Bio digesters are even drinking tea etc. despite there being a joint in the cover of the Bio Digester and the vent pipes have broken down over a period of 25 years of use. The average cleaning period is about 5 years. The tumbler and tea cups etc. can be seen by enlarging the Photos.

This attachment is hidden for guests.
Please log in or register to see it.

This attachment is hidden for guests.
Please log in or register to see it.

This message has attachments files.
Please log in or register to see it.

You need to login to reply
  • Kevinkuhn
  • Kevinkuhn's Avatar
  • Posts: 30
  • Karma: 6
  • Likes received: 17

Re: Regular septic tanks vs Biodigester septic tanks


I wanted to add a few things I learned about "Bio-Digester" toilets from my last trip to Ghana. There I met a few suppliers of these systems and got a more depth impression on these.

There are 2 main systems that claim themselves as "Bio-Digesters". Both share that they have one chamber were the solid matter gets digested and another chamber where the liquid overflow drains into the soil. The solids lay on a filter bed halfway in the first chamber. On this sheet (usually coconut) the supplier add either mulching, a bacteria mix, or macro organisms. All of them work with a pour-flush toilet.

One system (i.e. company Biofill) is using insects in the tank to reduce the volume of the solids. It wasn´t clear what the mixture is, but they said that there are earth worms and cockroaches. This is an aerobic system with a ventilation between the two tanks. There are rumors that the insects (especially the cockroaches) won´t stay in the system for long or leave at night. This sounds reasonable to me, and could be a huge vector problem. I couldn´t look into the system and could just ask question, but it seems to me that it is basically a tiger toilet with a second soaking chamber.

The other system is an anaerobic system. The two chambers are closed and oxygen is just entered through the toilet flush. The suppliers add a bacteria mix, which needs to be added every 6-9 months. They also use charcoal and mulch material to give as much specific surface area as possible for the bacteria. The biogas is not collected and just released through a valve.

Both systems state that pathogens are reduces and that the effluent is almost clean water. However I couldn´t get any results or prove from the suppliers. They just make clear that they build their system in a distance of 5-10 m to a well.

My perspective on the system is little bit mixed. I see advantages and disadvantages.
  • Reduces need of transportation by vacuum trucks, which is a big factor in these congested cities
  • It is a better treatment than having a septic tank where the vacuum trucks dump the FS into the environment and it is better than just having a soak pit
  • It is cost-effective for the low-middle income households
  • It uses a water flush, which is unfortunately still seen as a sign of development, but makes the adoption much easier

  • It depends on water which is simply not available at all times
  • The nutrients are either wasted into the air or go unfiltered into the soil. Recovery is impossible with this system.
  • The system is some sort of a black-box and the user (or anybody) doesn´t really know what is happening inside it
  • Although I can imagine some pathogen reduction, I find it hard to belive it fully without data. Otherwise it is a potential public health threat

In the beginning I was sceptical about this system. However I think there is a small space for this system for areas where there is
1. Enough water available
2. People are already "locked-in" into a water flush system, and a reluctant to switch to dry sanitation systems
3. Decentralized area without any proper WWT
4. Tropical climate

Interesting side note is that a current Woldbank financed program for urban sanitation in Accra is favouring/ subsidizing these systems. Seems like there will be a lot of these toilet systems in the near future and shape the sanitation landscape in Ghana and probably West Africa.

Best Regards
Non-Water Sanitation e.V. (english)

EcoToiletten - Rental for public composting toilets for cities and music festivals in Germany
The following user(s) like this post: nkunaj
You need to login to reply
  • Vivekvv08
  • User is blocked
  • Posts: 1
  • Likes received: 0

Re: Regular septic tanks vs Biodigester septic tanks

Hi i was much interested in making bio tank in my home. Kindly help me in the design and construction.
Thanks in advance.
Mail me: This email address is being protected from spambots. You need JavaScript enabled to view it.
You need to login to reply
  • Ashok
  • Posts: 42
  • Karma: -1
  • Likes received: 16

Re: Regular septic tanks vs Biodigester septic tanks

Thank you very much for your letter.

I am attaching a Power point presentation and a few links to You tube videos.

I hope this is what you are looking for.

The second video almost gives the step by step procedure for making and erecting Bio Toilets.

Cement ordinary Portland or Pozollona cement can be used.

Sand is ordinary river sand or stone dust can also be used.

If you need more details, I can provide that also.

I do not inject any inoculum.

These bio latrines have been in use for about 25 years in large numbers and users are happy.

Normally these latrines are emptied every five years.

I have also shared the above information with Mr Kinyanjui MbuguaNjonjo about a month back.

With best regards,

Ashok Jain Ph D


Web site:

Contact Numbers: 9919673410, 9643663392

E mail : This email address is being protected from spambots. You need JavaScript enabled to view it.

This message has an attachment file.
Please log in or register to see it.

The following user(s) like this post: nkunaj
You need to login to reply
Page selection:
Share this thread:
Recently active users. Who else has been active?
Time to create page: 0.406 seconds