Dear Osbert,

sorry for the late reply on your questions.

First, we do not measure colour of the wastewater. As we only treat domestic waste water we do not see any strong colouring. No dyes are in the waste water either.


I attach a picture pf the waste water sampled throughout the DEWATS plant, so have a look at it.


Regarding VGF HGF:

Sadly, both PGFs are connected in series, so we do not have a parallel comparison of each PGFs treatment. However, the VGF performs very good, yet, due to undersizing it, it is not meeting effluent discharge values for South Africa. A COD of below 100 mg/l is give ant any time though...as well as removal of TSS,turbidity and odour.


IF it would help you I could run the standard 3/5 point colour spectrum.

EDIT:

We do not capture biogas as it wasnt possible to get the settler gas tight. Additionally we experienced overboearing scum/Fog issues making it necessary to weekly open and access the manholes for maintenance.



Regards
Bjoern

Dear Seamus,


let me try togive an answer on your question.

I am the BORDA R&D Coordinator and a PhD student with Prof Buckley in Durban. I am conducting my research on the DEWATS demonstration plant you/Chris mentioned.


To your question:

The main COD reduction usually happens in the first 3 Anaerobic Baffled Reactors. A second degradation of about 10% COD happens in the first following Anaerobic Filter.
This can be seen in most BORDA plants around the world.


A probably high degradation is happening in the settler before the reactors, but, at the moment, cannot be sampled and analyzed.
Originally we tried to collect the biogas from the settler, but issues with pressure builtup and scum removal made this impossible.

I am saying COD reduction as we cannot measure the actual gas production in the reactors.
It also appears that a certain higher portion of the gas is not leaving the liquid phase but carried over to ABRs at the end.

If you have any further questions...i am happy to answer.
Sadly, I cannot share data as publication is the first step.
Attached find a graph with the results of 2 samplings of the reactors.

Additionally, to illustrate what is meant with scum in this context a short video I made of the !weekly! descumming procedure. Scum is meant in the terms of floating Fat, Oil & grease matter containing larger amounts of gasbubbles.




All the Best
Bjoern

Chris,
I read your report and it was very interesting. You mentioned maintenance and scum removal and loss of gas as a result. Do you or anyone else have an idea where methane production begins in the reactor. If it was in the second half of the reactor It should be possible to create a water trap to capture the methane gas and the gas from the first half of the reactor could vent. Any thoughts on this would be appreciated.

Regards
Seamus Kelly

Prof. Chris,
Thank you for posting this great work. Am particularly amused by the colour of effluent, physically is looks like drinking water. Could you be having values about the colour of influent and effluent. Where in the system was the highest removal efficiency in terms of colour. How do you compare the general performance of VGF and HGF. Then i dont know whether i missed this in the report, was the system continous flow? what is the inflow rate, HRT, SRT and biogas production rate?

Osbert

Greetings

The South Water Research Commission publication entitled "DEWATS PROCESS FOR DECENTRALISED WASTEWATER TREATMENT - Technical Lessons From eThekwini Municipality" has just been published.

You can download it here:
www.susana.org/lang-en/library?view=ccbktypeitem&type=2&id=2039

The municipality in conjunction with Borda and the municipal design consultants are designing DEWATS systems to treat the wastewater from Community Ablution Blocks serving informal settlements outside the sewered area of the municipality. The intention is for the treated wastewater to be used for agriculture or discharged to a water course (where no suitable agricultural land is available).

Additional information is available at prg.ukzn.ac.za/

Regards

Chris Buckley Pollution Research Group University of KwaZulu-Natal Durban prg.ukzn.ac.za

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