WEF Discussion Forums
Operation and Maintenance
MBR sludge condition
Has anyone had problems with localized dewatering in an MBR or organic fouling? Sticky sludge? process control recommendations?
We have been operating for about 9 months and found that the sludge quality has changed. Could be due to the temperature?, biological changes?, Solids wasting?, dewatering return stream?, etc or all of the above. I have not been able to find much information on what a good sludge is compared to a sticky sludge? how old is too old? too young? to thick? etc.
I have been doing some studies on the relationship between EPS and SMP in floc structure, and the differences in sludge condition related to each. Can you post a bit more operational information regarding this process? Parameters such as ORP and DO levels, SRT, F/M ratio and overall process flow scheme all make a difference in the ratio of EPS to SMP. Changes in this ratio can be responsible for an increase in "sticky" sludge, and a subsequent reduction in dewatering.
I look forward to your response.
The influent goes through fine screens into a channel combining with the return from the MBR's. It goes to an anoxic zone and then to an aerated zone, it is then pumped into the MBR. Things were working well when the temperature was above 17 C but started to have increased fouling in October. The solids had been in the system for about 5 months before we started a wasting program. We had to transfer things around while we wer under costruction. The SRT right now is about 70 days with an F/M of 0.02.
We are trying to maintain a DO of 1.0 mg/l in the aerated zone, It is much higher in the Membrane basin and is less than 0.2 mg.l in the anoxic zone.
We are looking into the level of soluble COD there is in the system but I am not really sure what that will tell us.
I am also using the microscope and staining slides to see if I can figure out good sludge vs "sticky sludge"?
It certainly sounds like the conditions are right for excessive fouling.
Can you tell me the current MLSS in the basins? You note an SRT of 70 days, and an F/M ratio of 0.02. Typical MBR F/M ratios run about 0.2, so your MLSS must be very high (unless that was a typo).
It wasn't a typo. F/M is about 0.02 with the MLSS between 13,000 mg/l and 15,000 mg/l. This is pretty common for an MBR sludge. It is a little above the design of 12,000 mg/l, because we weren't able to waste for awhile. We are trying to get down to 10,000 mg/l in the membrane basins.