Dear F H Mughal,
Thanks for your message. I really appreciate your advice and thanks for sending the documents on simplified sewerage system.

Regards

Paul

Dear Paul,

Somewhat unorthodox it may sound, I'm afraid, it is not quite right to connect the septic tanks.
Septic tanks are, quite often, connected to soakpits. The best solution in your case is the construction of small-bore sewerage system (simplified sewerage system).

I'm attaching some publications, which should help you out.

Good luck!

F H Mughal

Thanks Jan for the links.

The main objective of this project is to provide a proposal or proposals of systems that can be transitioned from onsite to offsite sanitation systems. If it can be implemented that would be a good outcome from this study. I am not considering septic tanks as the only solution as I am also considering flush urine diverting toilets and dry composting toilets where excreta can be transported for further treatment to local treatment points.

You are rigth about tackling the problem with water tightness now. I may consider having a combination of a simplified sewer system with a septic tank connection near the river banks. This would reduce the number of septic tanks being used and will help with desludging.

PaulUK wrote: Would you know a link to help me with the septic tank capacity calculations. I understand that some countries have specific requirements for building septic tanks.

That is true. I have no idea about the legal requirements and required building codes in Nigeria, but you can find plenty of information about septic tank designs here on the forum, e.g. in the following thread and the linked threads within:
TOPIC: Information about septic tanks, emptying frequency, and Wikipedia article

The Sasse book in DEWATS in Developing Countries might also give some general information about sizing: Sasse (1998) DEWATS in Developing Countries

But be aware about the concerns raised about using available standard formulas for designing septic tanks without considering the local conditions, as e.g. mentioned here: TOPIC: ABR-CW quick sizing tool
I would say, it's best to find someone local with experience in ST design.

PaulUK wrote: My research is to provide adequate sanitation systems to flooded prone areas which could be applied to communities living in similar conditions [...] for a community of around 120,000.

I am still not clear if you your project is just to "come up with a plan" or if it also includes the actual implementation/building of the proposed system. 120,000 people seems like pretty huge scale to me for supplying with septic tanks in a MSc project. Or is your work part of a bigger research/funding scheme?

PaulUK wrote: I have read about [simplified sewers] but I was not sure if it could be applicable to flooded prone areas and the number of inspection chambers required will be quite large for a community of around 120,000.

If the ultimate plan is to connect all households to a centralized sewer system in the long-run anyway, you will sooner or later have to tackle that problem of water tightness and number of inspection chambers anyway. So, why not account for that already in the first stage - less headaches some years down the line...

Thanks Jan for your reply and advice provided. It is very helpful
With regards to your questions,

'will it be a proposal you are preparing or is there also time and funding for implementing a system in the area your are looking at?'

My research is to provide adequate sanitation systems to flooded prone areas which could be applied to communities living in similar conditions.

'It appears to me, that you are trying to rely on gravity flow only, is that right?'

Due to lack of infrastructure for water/sewage treatment I am looking at natural ways to incorporate a system into the community with the less use of energy if possible ( e.g. electric pumps)

'Did you consider Simplified Sewers or something similar, yet? '

I have read about it but I was not sure if it could be applicable to flooded prone areas and the number of inspection chambers required will be quite large for a community of around 120,000.

Once again thanks for your comments. Would you know a link to help me with the septic tank capacity calculations. I understand that some countries have specific requirements for building septic tanks.

Thanks

Paul

Hi Paul

Interesting thesis project; will it be a proposal you are preparing or is there also time and funding for implementing a system in the area your are looking at?

From a quick look at your drawing, I would say that it won't really be possible to transfer the sludge and scum from one septic tank to the next without the use of mechanical equipment. It appears to me, that you are trying to rely on gravity flow only, is that right?

I guess you could have the (liquid) effluent from the first septic tank be flowing into the second, and then third and so on; but you would need bigger and bigger septic tanks to handle the increase in hydraulic load and decrease in pollution concentration.

You might be able to connect all three toilet complexes into a single septic tank, but you would need a relatively higher gradient in the sewer pipes transporting raw sewage compared to septic tank effluent; your head loss will depend on the length of the sewer line and the type of wastewater you're transporting.

Did you consider Simplified Sewers or something similar, yet?
The Wikipedia article has a basic overview (not great, but asome place to start): Wikipedia- Simplified Sewerage

But I understand that the coastal location might be a constraint in how "deep" you can go.

Hi Marijn,

Thanks for your reply. You are right. I should not have include a urine diverting toilet. That is part of another proposal I am considering. In this case it would be a normal flushing toilet. I am looking for a sanitation system that would be most effective to be transitioned to a sewage pipe network in this particular slum built on water. There is a proposal to introduce sewage pipes in the future but at the moment I am concentration on an onsite system which could be easily transfered to a pipe network when this occurs.

The community I am studying is a slum built on water by the coast in Lagos. There is a problem with high and low tides and they dont have access to a water/sewage network. I am dividing the community into different sections where a number of dwellings will share a communal toilet (e.g. having 4 toilet compartment and two separate cleaning facilities for women). The proposal I want to make is to connect these toilets to a fibre glass septic tank and faecal sludge removal will be done by truck from dwellings which are close to dry land. I am looking for a way to reach dwellings who live far from the coast and I wanted to know if septic tanks could be connected together in a way that the outputs (picture attached) of one septic tank will be the inputs of the next septic tank plus the input of the communal toilet. At this point I am not sure if this is possible as I am still trying to understand the capacity/size and flow rate for each septic tank. I have attached a picture of what I wanted to do if possible.

This proposals are part of my MSc project I am working on so I am trying to provide onsite sanitation systems where the local community can work together with the local government (eg government providing drinking water and sludge collection in return of a monthly fee paid by the community).

Hope this better clarifies what I am trying to do.

Thanks

Dear Paul,

I think you may have to be a bit more specific about how you envision your system and what your actual question is for people to be able to help you in a good and constructive way.

Regards

Marijn

I wanted to know if it would be possible to connect septic tanks together and the technicality of it. I want to provide a sanitation system in a slum built on water using flush urine diverting toilet. Dwellings far from the coast line will be mainly affected as there is not any type of sewage pipe infrastructure.
Thanks