Dear all,

Sorry for the slow reply.

The biggest concern with the disposal of ash I see are heavy metals because most of them accumulate in the ash (except for mercury which is volatile and might leave during combustion with the flue gas). This is for a example a concern for combustion of wastewater sludge. As wastewater is commonly mixed wastewater from households and industries it has high concentrations of heavy metals which accumulate in the ash. in Europe/North America, this ash is disposed in landfills. I do not know of any standards for disposal of ash from wastewater or faecal sludge combustion. Maybe you should talk to the national environmental management authority. I guess they are responsible to monitor and regulate any pollutant discharge.

Faecal sludge is commonly only from households. This means that heavy metal concentrations are low. However, this might depend on the local context. We looked at heavy metals concentrations in dried faecal sludge in rural and peri-urban Ghana and urban Uganda and Burkina Faso. Heavy metal concentrations were elevated (but lower to wastewater sludge) in urban areas. In rural areas, heavy metal concentrations were low. Therefore, I think ash from combustion of dried faecal sludge can be disposed/used in agriculture if any heavy metal contamination can be avoided (and ash quantities are low).

I like to point out that dried faecal sludge might have high concentration of nitrogen, sulphur and chlorine. During combustion this could lead to emissions of nitrogen and sulphur oxides, dioxins and black carbon and problems with corrosion (because of formation of hydrogen chloride). This suggest that incineration of dried faecal sludge may be most appropriate for large-scale industries (e.g. cement and brick companies) which can control these emissions. However, I am sure it is also possible at a smaller scale (e.g. the 500 people you mentioned).

I hope this helps.

Best regards,
Moritz

Dear Jos,

Elisabeth has a valid point. You must look into that. Incineration, after all, has its share of problem, especially when it is located close to human population.

Cheers,
F H Mughal

Oh, but why would you want to incinerate the sludge when the treatment plant is so small (500 people)? This is far too small to make incineration worthwhile. Why not just dry the sludge in sludge drying beds in that case? After drying and possibly composting you could reuse that sludge.

Don't forget the big question of who would operate and maintain such a plant in the longer term.

Dear Mr. Mughal and Mrs.von Muench,

Thanks for your helpfull tips, ; You also gave me a lot of research work to do.

I would like to be more specific about my question.

My company wants to install a sewage treatment system for a 500man compound in Mali where soldiers are for a UN-mission (Minusma).
But we want to do this on the most sustainable way with a "zero footprint" in the country.
Our idea is to install an incinerator but we end with the ash problem. Either we looking for a sollution on location or the surroundings of the compound, or we have to ship these ashes to Europe where we have other problems with custom etc.etc..

The water treatment plant has an outcom of purrified water that could be spread on surface as part of an agriculture project. Maybe the ashes can be diluted with this water.

Looking forward on your advice about this solutions and I'll look at the links you both gave me.
Thanks again,

Jos

WE have many kilns in Punjab, where they make bricks.
That was a good review - Thanks, Elisabeth

F H Mughal

Speaking of cement production, this reminded me of the FaME project by Eawag and partners in Uganda, Senegal and Ghana. Please see here:
forum.susana.org/forum/categories/53-fae...gal-uganda-and-ghana

I copy a quote from Moritz's first post in that thread:

Pilot-scale kilns* were constructed in Dakar and Kampala to research the use of FS as a combustible. The pilots will compare combustion of FS with other local biofuels in use. The pilots will provide the first scientific data on combustion of FS in the context of developing countries.

* I didn't really know what exactly a kiln is, so I turned to Wikipedia which says:
en.wikipedia.org/wiki/Kiln

A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Various industries and trades use kilns to harden objects made from clay into pottery, tiles and bricks.[1] Various industries use rotary kilns for pyroprocessing—to calcinate ores, produce cement, lime, and many other materials.

Publications are also here on their website:
www.eawag.ch/en/department/sandec/projec...agement-enterprises/

The FaME project is now completed, currently they have a follow-on project called SEEK (Sludge to Energy Enterprises in Kampala: Innovative resource recovery from faecal sludge), see post by Moritz here (page 2 of the same thread):
forum.susana.org/forum/categories/53-fae...it=12&start=12#11130

Website of that project:
www.eawag.ch/en/department/sandec/projec...erprises-in-kampala/

Actually, I will ask Moritz if he could give us an update about the SEEK project here on the forum.

Anyway, perhaps this gives you some useful leads?

Regards,
Elisabeth

Dear Jos,

Elisabeth has given a good picture of ash in developed countries. In developed countries, it is different.

Please read this carefully:

What we get from municipal (when I say "municipal," I mean non-toxic) wastewater treatment plants is treated sludge from secondary sedimentation tanks. This sludge is sun-dried in sludge drying beds. What we get then is the dried sludge. The sludge is used as soil conditioner.

We do not incinerate this sludge. Since, we have plenty of sunshine and the weather is relatively hot here, we resort to sludge drying. We don't have regulations here for this.

Generally speaking, if you have non-toxic ash, then, it can be used, as you said, in cement production.

For regulations, please try your luck at USEPA website; and UNEP chemicals in Japan
(www.unep.org/dtie/Branches/ChemicalsandW...d/29687/Default.aspx)

Regards,
F H Mughal

Dear Jos,

Could you please provide a bit more context to your question? In particular:

1. Which country or countries are you referring to?
2. What kind of sludge are you referring to? Sewage sludge or fecal sludge?

I think that makes a huge difference. E.g. in Germany you'd find that a lot of sewage sludge is being incinerated and the ash is for sure not used as fertilisers on fields. I am not totally sure but I would guess it is either landfilled or "locked into" something else, e.g. production of bitumen perhaps (or cement, as you said)?

There are probably lots of publications on sludge incineration in industrialised countries. There is a short bit of information on Wikipedia here (perhaps a useful starting point):
en.wikipedia.org/wiki/Sewage_sludge_treatment#Incineration
en.wikipedia.org/wiki/Sludge_incineration

Actually this page looks quite useful, it is for incineration of waste but I think the information about the ash could be interesting for you:
en.wikipedia.org/wiki/Incineration

But I am guessing you are referring to developing countries, where probably sludge incineration is far less common and regulation perhaps not as well developed yet? I doubt that WHO has published anything on this subject (but I haven't done a search yet)?

Regards,
Elisabeth

Mr. Mughal,

Thanks for your reaction. Your reaction can be translated as: ash from a normal sewage treatment system that ends with a incinerator is accounted "not toxic".
But now my question is: What is normaly done with that ash ? Used as fertilizer or used in cement for example? Can you provide me with some oppertunities ?
Thanks

According to my information, if the ash is from incinerator that is used for hospital wastes, or toxic industrial wastes, then the ash, both the bottom ash and the fly ash, would still be toxic, and need to be disposed off in an engineered landfill.

F H Mughal

I would like to get some information about the regulation about handling of the ash that is the residu of sludge burning.
If the sludge is heated enough, most toxic and pathogens will be gone, so the ash might be accounted safe.
Now is my question: Are there any (WHO)regulations about spreading these ashes on fields and if this is forbidden, are there custom regulations about transporting the ashes to an other country.
Any information is welcome.