Time taken for faecal sludge tankers to discharge?

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  • Elisabeth
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Re: Time taken for faecal sludge tankers to discharge?

This has been a really interesting thread, thanks to Kevin for raising this topic with us and thanks to everyone else from around the world who has responded!

I was doing some work on the Wikipedia article on vacuum trucks today, so I added a section on emptying of the truck.

I have two dilemmas here:
  • I have no reference to cite (this forum thread doesn't count as a reference on Wikipedia)
  • I might have added more detail than what a layperson would need to know
But in any case, I have added it (=a bit like a summary of this thread), and let's see if it sticks. Perhaps someone will find a reference for this information in future, too.

So this is how I have written it, hopefully understandable for lay persons:

en.wikipedia.org/wiki/Vacuum_truck#Emptying_the_tanker

Emptying the tanker [edit | edit source]

Normally a tanker is emptied by gravity. There is a possibility to pressure up the vacuum tank in order to “pressure out” the liquid quicker or against a small difference in level. But that procedure is not good for the equipment and is therefore done only in special situations.

The regular discharge time for a tanker of 8 – 9 m³ is about 15 minutes (or 7-10 minutes to unload a tanker of 4000 liters). The outlet is typically 4 to 6 inches (10 to 15 cm) in diameter. The discharge time depends on the thickness of the sludge, the size of the outlet valve and hose, the amount of garbage in the fecal sludge and how often the driver has to stop to clean the dump screen.[citation needed]


Comments welcome, also feel free to modify it directly in the Wikipedia article itself.

Regards,
Elisabeth
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  • kevintayler
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Re: Time taken for faecal sludge tankers to discharge?

Dear Christoph

Thanks for this. I am currently in Dehradun, India and had a chance to observe a tanker discharging into a sewer on Friday. The tanker capacity was 4000 litres and the outlet was 100mm but they connected a 75m hose to the outlet and dropped the hose into the sewer. That would have increased the head at the end of the pipe but on the other hand there would have been friction in the pipe. The tanker took about 3 minutes and 30 seconds to empty the tanker (assuming it was full which may not have been the case). That equates to about 20 litres per second which is in line with theoretical calculations using orifice theory (albeit ignoring the effect of the hose). The Brazilian experience, along with many of the others referred to in this thread, is that discharge rates are less than this. I think that the overall conclusion is that, whatever the theory says, there is no substitute for recording actual discharge rates - thicker sludges may well take longer to discharge.

One point Christoph is that you do not mention the size of the outlet, I would guess 100mm but it would be good to confirm

Regards to all
Kevin


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  • christoph
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Re: Time taken for faecal sludge tankers to discharge?

Dear all,
just some quick comments.
Background: We (Rotária do Brasil) operate 3 tankers and we are part of an association for sludge emptying with 26 tankers in southern Brazil. We operate at one treatment plant.

• The regular discharge time for a tanker of 8 – 9 m³ is about 15 min.. quite similar to the practical numbers mentioned here.

• What is “pressure out”? Normally a tanker empties by gravity, that is better for the equipment and uses less gas. If needed there is the possibility to pressure up the vaccum tank in order to “pressure out” the liquid quicker or if you have to empty against a small difference in level. But that procedure is not very well accepted as it is “stressfull” for the equipment, so it is done only in special situations.

Hope that complements the picture.

Regards
Christoph

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  • Reetu
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Re: Time taken for faecal sludge tankers to discharge?

Thank you Kevin for your kind appreciation!

Just wanted to add, unloading was made by the gravity flow as there is no control valve at the outlet.

Kind regards
Reetu

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Re: Time taken for faecal sludge tankers to discharge?

Thanks Reetu

Your information is useful. It confirms what has become clear from other people's information that it takes longer to discharge than suggested by theoretical calculations based on orifice theory. This may be partly due to the point already made by Shaji that the operators do not always open the valve fully to avoid splashing. I think it means that I will remove the theoretical graph from the book, give some typical discharge times based on information received from you and other people and emphasise the need to design inlet facilities using recorded discharge times

Thanks again
Kevin
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  • Reetu
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Re: Time taken for faecal sludge tankers to discharge?

Hello Kevin,
This is late now but just wanted to share unloading time in context of Nepal.
We, Environment and Public Heath Organization (ENPHO), had done questionnaire survey with the sludge emptier of Kathamndu valley, capital city of Nepal, and also recorded the time of unloading by ourselves. According to them and from our experience, it takes 7 to 10 minutes to unload 4000 liters of fecal sludge(FS)from 6 inches diameter outlet hose depending upon the proportion of solid and liquid matter in it.

Looking forward for your publication.

Reetu
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Re: Time taken for faecal sludge tankers to discharge?

Thanks Shaji

I am going to be in India for a workshop on FSM next week (Dehrahdun) so will follow up with people at the workshop. The point you make is an important one

Kevin
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Re: Time taken for faecal sludge tankers to discharge?

Dear Mr.Kevin

Looking forward for you publication.

The rate of discharge of septage from the truck also depends where material is being dumped. If it is a drain the truckers happily discharge at the maximum rate while when ever they are asked to discharge into a specific pit they take enough time to ensure that there is no splashing. As the regulations are becoming more stringent over the period and with increased awareness among the trucker community the time taken for discharge is also increasing.

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Re: Time taken for faecal sludge tankers to discharge?

Thanks for the suggestions Mughal

There is not a specific chapter in the book on climate change but I will be trying to say something about the benefits of technologies that reduce climate impacts.

Thanks for the holiday wishes

Kevin
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  • F H Mughal
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Re: Time taken for faecal sludge tankers to discharge?

Dear Mr. Kevin,

Thank you for the background information, regarding your publication. It was helpful and interesting. Yes, I would be delighted to receive a copy for review.

I have a small suggestion. I think, it would be extremely beneficial, if you kindly add a chapter on climate change impacts on FSM, and how to adapt and build resilience. That is an important aspect for people in the South, and even from London's point of view.

I, too, noticed that you have been not quite active these days - now I know why!

Enjoy your upcoming holidays! :)

Regards,

F H Mughal
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Re: Time taken for faecal sludge tankers to discharge?

Hi Mughal

The book is to be published by Practical Action Publications. The World Bank and the Gates Foundation are providing some funding for the publication and I think that this will be used to make it reasonably freely available. I have not got the contract yet but I am sure that the copyright will be with the publisher so the availability of the final version will be up to them. However, I think that it is going to be possible to make electronic copies available, at least to people in 'the South'. I am due to finish the first draft by the end of the first week in January and it will then go out for comment from reviewers with the intention that I get comments back by say mid-February and aim to complete the final draft in March. I can send you a copy of the draft for review - it would be good to get comments back from you and others on the forum. I can email material once it is ready.

I am afraid that I have not been very active on the forum lately - mainly because the book is taking up a lot of my time

Regards
Kevin
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  • F H Mughal
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Re: Time taken for faecal sludge tankers to discharge?

Dear Mr. Kevin,

I'll be looking forward to your publication on faecal sludge treatment. I assume, you will share your publication on this forum.

To have a broader scope, it might be appropriate if you title your publication as: Faecal Sludge Management and Treatment. What do you think?

Regards,

F H Mughal
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