Scum Management

[Kowycz]

I am currently working on a WWTP upgrade and my supervisor and I are running into a problem deciding what to do with the scum out of the primary clarifiers.

Currently the scum is skimmed into a trough and routed into a "scum concentration box." Once the grease and scum coagulate the material is then removed via manual labor.

My supervisor is considering removing the scum out of the concentration box via a chopper pump and recirculating it back through the plant or piping it into the proposed liquid sludge storage tank. [NOTE: After the liquid sludge storage the sludge will be thickened and ran through an ATAD System]

I am green behind the ears being a recent college graduate and have little valuable opinion on the situation. I however did want to research it the best I could to help his decision.

I was also interested in learning what is typically done on new construction jobs as well; merely for my own learning purposes. Most literature just mentions removing scum out of the primary clarifiers but doesn't mention what happens after that.

Thanks for your time,

Matthew Peters

 

[bimr]

Scum handling and disposal is a significant problem at most wastewater plants. Scum has odors and is not visually attractive.

You best option is to install a heated decant tank to collect the scum. You can then have the scum sent offsite for disposal after you have decanted the free liquid. A disposal vac truck can suck the material out of the decant tank. No shoveling involved.

Scum handling is frequently overlooked. Many plants do not process the scum. It is collected and then shifted somewhere else in the treatment plant where it may cause other problems. Scum tends to move around in the treatment plant and then return. You are better off just removing it and sending it off for disposal.

There are numerous treatment schemes for scum. These include anaerobic digestion, incineration, chemical fixation with lime,

The best value for the average treatment plant is sending it off site for processing and disposal.

 

[SteveWag]

Your ATAD will just love the scum; the heat value is very high. The problem is that an ATAD (at least mine) will not like the extra water that may go along with the scum. As "bimr" stated, scum handling is often overlooked. Recycling sludge just makes matters worse. If the sludge and scum can be thickened together, then best would be to route the scum to the sludge holding tank. Another method I have used is to introduce (meter) the scum into the thickener feed, mixing it with the sludge. This keeps the scum out of the sludge holding tank. Some operators like to decant from the sludge tank as part of the thickening process, scum often clogs or otherwise interferes with the decant process. I have used 3 and 4-inch peristaltic pumps for this mixing design. They offer adjustable flow rate and have the ability to run dry. I try to take the suction from the bottom of a hoppered scum tank and remove the entire contents of the tank (remember, scum, by definition, floats). In doing this I can also hose down the, now empty, tank. Very few designs I have seen allow for complete emptying of a sludge holding tank, and if not drawn down dry, the scum cannot be removed.
Steve

 

[msquared48]

This sounds like a political topic to me.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[QualityTime]

Mix it and pump it via chopper pumps to a remote scum concentrator. The scum concentrator would be relatively shallow and have a beach plate a chain and flight mechanism. Scum floats and the flight would scrape it up the drying beach plate and it would empty into a bin for disposal off site. A lot ot fhe New York City WWTP's use this method

 

[QualityTime]

Go to this site to see what a scum concentrator is all about. In New York they don't have the holding tank. The scum spills over into a bucket similiar to what trash metal haulers use. The same vehicle that is used to lift trash metal buckets is used to pick up and haul the scum bucket off site.

http://www.envirocare.com/files/ScumBro.pdf

 

[sow]

Ive seen plenty of works that pump the scum to the sludge tanks for mixing prior to thickening /dewatering or just straight to dewatering. Ask the suppliers of your dewatering equipment what they think.

Problem is that scum can take a lot of water to move and / or unblocking of pumps - but it sounds like it may be worth while and not uncommon. Could you trial it first?