What are probable causes of floating sludge in a clarifier?

Answer 1

Low rates ow WAS and RAS can cause sludge to float on secondary clarifiers. You should increase the rate of WAS and RAS.

Answer 2

1. Check to see if the clarifier is level in both planes, front to back and side to side. It is possible that, over time, the floor or the clarifier’s foundation has settled unevenly, causing more wastewater to flow through one pack versus the other. This higher flow means a higher velocity through the plate pack, causing the lighter floc particles to be carried out into the effluent. If you find that it is out of level, we recommend that you re-level the clarifier. Some models have overflow weirs that are adjustable, while others will require the entire clarifier to be leveled.

2. When was the last time the settling plates were cleaned? At least monthly, and possibly even more frequently, we recommend that you pump down the clarifier until the wastewater level is below the bottom of the plates. Thoroughly rinse off the plates; if you have access to a high-pressure washer, use it. If the plates are not periodically cleaned, floc can accumulate on the plates and even block some of the passages between them. This forces the wastewater to pass through fewer plates, resulting in higher velocities and more floc carryover.

3. When was the last time the entire clarifier was cleaned? At least annually, and possibly even every six months, the clarifier should be entirely pumped out and the bottom section cleaned through the side access hatch that most clarifiers have. Over time, floc can build up and become compacted into the clarifier’s sides below the plates and if not removed will reduce sludge storage volume. Also, floc can build up on the influent distribution structures that slow down the incoming flow and distribute it evenly along the bottom of the plates; this build up will eventually disturb this incoming flow and cause floc carryover into your effluent.

4. Have you checked to make sure your flocculant or polymer dosage is not excessive? Excessive polymer can accumulate on your clarifier’s plates, acting as a glue and attracting excessive floc particles, which no longer easily slide down the plates and remove from wastewater. Again, the floc builds up, causing higher velocities up through the plates and causing excessive solids carryover. Rub your fingers over the plates; if they feel really slimy, then check your flocculant dose.