Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
June, 2012

Multi-Stage Grease Trap

Q. We purchased a food manufacturing plant that was built without a sewage treatment system. We are located in a park where theres a centralized stp. The city requires us to pass their standard.

What method can I use to drop COD, BOD, color, TSS, oil and grease value?

Can a multi-stage grease trap help me to drop them all?

I was thinking that since BOD and COD might be cause of food crums and other ingredients being washed, an installation of grease trap for every area will help me collect most of the pollutants and help me drop the COD and BOD. I have not tried it though, since it will cost too money if my idea is wrong.

A. If you had a cheap, easy, somewhat continuous, or as needed (depending on production) mechanical way to remove solid "solids", and grease and oil before it turns into dissolved solids, or dissolved BOD and COD, then YES it would help reduce the BOD and COD, and TSS, and obviously would reduce Oil and Grease, but the % reduction, would depend on how much there is that is not already dissolved.

I have seen cases where the oil and grease, and solid solids, like blueberries, marshmallows...., was a huge number and was well worth mechanically removing first (reductions of 65-70% are possible), with screens and separators. The longer those solid solids are in contact with the waste water, the more they will be dissolved by bacterial enzyme action, adding to the dissolved pollution parameter problems, especially the BOD. You might also look at soaps and detergents you use, as they add to the COD, BOD, Oil and Grease and TSS, as they have their own BOD and COD, and they can emulsify variable amounts of Oil and Grease, called O&G, and thus can raise the discharged BOD, COD, TSS and O&G by 200%. So you might test various detergents to find one that has the lowest emulsifying potential and the lowest COD.

Best Regards,

Mike McGinness