Interesting questions, but ...
Published by Thomas Nangle
1 Comment
The dewatered sludge is actually transported to a landfill site. Here in SA we pay per volume sludge transported. To reduce the volume we dewater. Poly is added to increase the dry cake solids by aiding separation of water and sludge. The feasibility will be investigated in the futerture of making a central Biogas facility and instead of transporting sludge to landfill, it is transported to the facility. However, this sludge will contain poly and the poly is diluted with chlorine treated water. The feed to the digester will therefore have poly and this cannot be changed. I have asked this question to many at seminars but none that I spoke to have researched this parameter.
Published by Ghoewylah Darries, Process Engineer at NuWater
2 Comments
Thank you for clarifying, this makes more sense. I agree with John that you shouldn't have to worry about the chlorine, because the small residuals affect on the digester sludge will be negligible.
I too have not heard of any studies into the effect polymer has on biogas production. Here in the US, we often thicken sludge prior to anaerobic digestion to increase the solids throughput capacity of the digesters. The thickening processes include polymers. Like I said above, I haven't heard of any studies on the effect polymer has on anaerobic degradation, but I would venture to say that there isn't a large enough effect for anyone to take notice and decide to run some pilots. If you do run any tests, I'd be interested in seeing the results.
Sounds like you may be thinking of a dry anaerobic digestion technology for the biogas facility if you will be feeding dewatered sludge. If the sludge isn't hydrolysed prior to a liquid anaerobic digester, the solids feed would be capped around 5-7%, due to pumping and mixing limitations. I'd guess you currently dewater sludge to 15-30% solids.
Sounds like a cool project, where is the project located in South Africa?
Published by Thomas Nangle
I'm assuming you can't build the biogas facility next to you WWTP, correct? Otherwise you would just be able to pipe it directly from the digester and bypass your cost to belt press and transport. But to answer your first question, NO it would not hurt the biomass simply because by the time is enters the system the chlorine would have either been used up or gassed off. THe demand of the sludge would be so great it would overcome any effect from a 0.25 mg/l concentration which is close to drinking water standards at the tap.
Published by John Foris, Certified DW and WW Operations