Kenya NEMA environmental discharge standards

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  • jdtwilcox
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  • Environmental design engineer. Currently researching urban sanitation economics at University of Leeds. Previously with Sanivation, Kenya and UK water industry.
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Kenya NEMA environmental discharge standards

Hi all -

I am reviewing some faecal sludge treatment options in Kenya and using the NEMA Monitoring Guide for Discharge into the Environment (link below). I want to check my interpretation of the third and fourth schedule -

Domestic sewage systems (and I assume this will include faecal sludge) are limited at:

- BOD - 30mg/l
- TSS - 30 mg/l
- pH 6.5-8.5
- coliforms/ecoli - nil 
- oil & grease - nil
- COD - 50 mg/l
- colour/dye/pigment - 15 hazens ?
- total phosphorus - 2 mg/l (guideline value?)
- ammonia - 100 mg/l (4xNH4-N+NO2+NO3)
- copper - 1 mg/l
- free available chlorine - 0.1

I am comfortable with most of the limits but uncertain about the phosphorus and ammonia permitting.

Most conventional / standard treatment systems for wastewater and faecal sludge won't reduce total phosophorus to 2 mg/l - is this standard typically applied? 

The way that ammonia is permitted appears relaxed (100 m/gl) but I'm concered that:
- without nitrification the concentration in both wastewater and faecal sludge treatment effluent would exceed the calculated value
- with nitrification although the weighted value of ammonia is reduced I'd still expect there to typically be enough nitrite/nitrate to exceed 100 mg/l  
- denitrification is fiddly

Am I missing something? Any reflections / discussions on this would be great / appreciated!

Many thanks, Jonathan

extwprlegs1.fao.org/docs/pdf/ken84962.pdf
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  • ErikTN
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Re: Kenya NEMA environmental discharge standards

Hi Jonathan, 
Feacal sludge treatment is being designed in many places in the tropics, so your questions about the environmental discharge standards are very relevant for many. 
I can not contribute to the specific questions about phosphorous and ammonia but is interested if you have found some answers since the first posting. 
Regards, Erik
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  • jdtwilcox
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Re: Kenya NEMA environmental discharge standards

Thanks Erik for your message.

I haven't made any progress on this yet but will provide an update if I learn anything.

Thanks, Jonathan
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  • Elisabeth
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Re: Kenya NEMA environmental discharge standards

Hi Jonathan,

I agree with you, these two parameters for environmental discharge standards are surprising:
- total phosphorus - 2 mg/l (guideline value?)
- ammonia - 100 mg/l (4xNH4-N+NO2+NO3)

The total phosphorus value is very low and would be hard to achieve for most BNR plants (BNR = biological nutrient removal). Also, depending on what the effluent is meant to be used for, it might be unnecessary to go to such low levels of P. 

Do the guidelines distinguish by the type of receiving water body or reuse application?

The figure for ammonia is also confusing to me. I am used to seeing either a value for total nitrogen (TN) which might be something like 5, 10 or 20 mgN/L. Or a value for ammonia-N which might be less than 1 mgN/L. So normally the nitrogen component of the molecule is taken as the measure, not the overall molecule.

I'd have to look more deeply into it to understand what is meant with 4xNH4-N+NO2+NO3 here. Maybe someone else from Kenya or similar countries could help.

Either way, getting the N and P content of the supernatant that remains after faecal sludge treatment steps of thickening/dewatering to very low levels would require quite some advanced, well operated treatment system. What are the treatment steps that you plan to apply? 

Regards,
Elisabeth
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