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RE: Sudden Plate and Frame Dewatering Problems

TerryF — Mon, 14 Apr 2008 17:47:35 GMT

Whislt i don't have a specific solution you need to think through the how the various coagulants etc work. Ferric chloride typically works by forming a hydroxide sludge that acts as a sweep floc whereas the polymers work by charge neutralisation and bridging.

In operation Ferric will be very pH dependent whereas the polymers , whilst pH sensitive will be less so. The initial choice of polymers is often dependant on whether the solution is acidic , or basic however.

Generally Ferric Chloride will allow a far amount of flexibility with changes in dose rates and alteration/control of pH required when conditions change. However many polys are much less tolerant of changes in conditions and may work only in a narrow window.

Your records may indicate changes to background pHs , temperature , alkalinities and these may give a hint at why certain coagulant mixes are not working. As someone else has suggested changes in background conditions may be impacting on the process.

Hope this helps although i have been deliberately general in my comments.

Regards

TerryF

RE: Sudden Plate and Frame Dewatering Problems

Milos — Mon, 14 Apr 2008 11:56:50 GMT

Try the combination of lime (first, dose to pH 8,5 - 9,0) and cationic polymer, (or cationic and anionic polymer) in the jar tests.

And different temperature conditions (in the biological tanks) may change dewatering characteristics of sludge.

Sudden Plate and Frame Dewatering Problems

Brett Ward — Mon, 14 Apr 2008 09:30:34 GMT

Help and ideas needed to trouble shoot a sudden dewatering problem with a plate and frame press. The process in an oxidation ditch followed by aerobic digestion. The WAS is first pumped to primary digester then to secondary digester from which the press is feed. Traditionally a ferric chloride poly quant blend cationic polymer has worked well in the presses, but each spring in late March or early April the process fails. Regulators have pointed the finger at an industry that used to discharge acids and oily water to the system. In past years the addition of bentonite clay always improved the press performance, but not this year. Our polymer consutlant says that the imporvement using bentonite is proof of oil in the sludge. This years jar tests are strange. We can make a floc only when the pH is above 10 su. When the pH drops the floc disperses. Jar test using anionic polymer were no better. There have been no unusual changes to the oxidation ditch and effluent quality remains good. BOD and TSS < 10, ammonia <1.0 Clould this be weather related? Thanks in advance.