Been having transmittance problems with my UV disinfection, high fecal counts. Possibly due to the effluent being cloudy? Also have some bulking going on in the clarifier. Extended Aeration Plant is in parallel operation. Influent goes through headworks to EQ Tanks (DO <.5), through D-Box to 2 oval oxidation ditches with mechanical aerators operated automatically by DO Probe/SCADA. 2 30ft Clarifiers with the sweep arm making a single rotation in about 15-20 min. Then to UV Disinfection and then discharged. RAS is sent back to the EQ Tanks.
Inf: BOD 303mg/l, TSS 260mg/l Ammonia 56mg/l
EFF: BOD 5.6mg/l, TSS 8mg/l   30min Settle - 340  Ammonia .5mg/l   DO >4.0mg/l
AVG Flow .175mgd
MLSS 3300, RSSS 4200
DO in Oxidation ditches 1.8mg/l
SV!: 77 & 97      SA: 13days
Anyone have some ideas to clean up the effluent cloudiness and stop the bulking in the clarifiers?

Idea of sending the RAS to the EQ Tanks was to create an anoxic zone to help with ammonia removal.

I agree with Steve's advice about not sending the RAS to the EQ tank.  If the RAS spens too long, or not enough time in a selector it is not effective.

Is it possible to cycle the aeration- with the time when they're off for denitrification under anoxic conditions?- better yet would be to create an anoxic zone in your ditch.  

Is your RAS turned up as much as possible? How high is the sludge blanket? A microscopic evaluation of your sludge would be extremely helpful in troubleshooting. The fact that you describe the supernatant as cloudy raises a red flag- if it's filamentous bulking the supernatant should be very clear- also your SVI doesn't seem to be horribly high.

Is it cloudy on the settleabilty test as well as in the clarifier? Does the sludge settle rapidly (with the first 10 minutes) or does it take the whole half hour or even longer? Personally I'd like a little bit more info before I decide to increase the wasting rate.

ok- I understand your reasoning now he'll just need to be sure that's the cause of the cloudiness and not something else like increased load the plant or some kind of toxicity.

I really appreciate all of the help. We are going to be wasting more.
The RAS is at 100% all of the time, it's either all or nothing. The sludge blanket is about 1ft and the 5 min settleometer is about 550.
My capabilities for doing a microscopic evaluation is limited, sending a sample to be evaluated sounds like a good idea.

I am a new operator and have just taken over a plant that was run out of design for quite a few years. It has been put back into design process along with some recent upgrades. First time the plant has run in parallel with the upgrades so it is all very new.

Trip510,
What do you mean by "bulking" in the clarifiers?

Your SVIs are low, do you mean rising sludge due to denitrification?

Can you send your RAS to the the point where influent enters your ditch?

Where do you measure your DO in the ditch - how close to the aerators?

Your scraper speed - can you be more precise?

Cloudiness in my opinion is due to any or all of the following (taking into account your quite good effluent figures):

• over aeration
• excessive sludge age
• over-chlorinating for SVI control
• plant recovering from a shock/toxic load

Cheers

Trip510,
Your clarifiers are not the problem - good scraper speed there.

Your DO of 1.8 mg/L upstream of the aerators is a concern.  An oxidation ditch (that is required to nitrify and denitrify) should have a DO of about 1-2mg/L for say 40 to 60% of the length - the portion of ditch upstream of the aerators should have a low DO, typically less than 0.3mg/L to drive denitrification.

It is best do a DO profile along the whole ditch (a reading every 10% of the toatl length) rather than at one point so you can get an idea if your anoxic zone is adequate in size.

I'd say get the DO down a bit, upstream of your aerator for starters.

Cheers

A combination of long sludge ages and over-aeration can produce damaged floc which looks like numerous pin head sized pieces in the effluent so the effluent is not as clear as it could be.  

Also we have to be clear on what you mean by "cloudiness".  If you under aerate you can end up with a slightly milky appearance in the effluent.  This would also mean the effluent BOD was too high.  In the example quoted in this post the effluent BOD was low so under-aeration was not the issue.


Cheers