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

by Mike McGinness, EcoShield Environmental Systems, Inc.
November, 2006

Oily Waste to Anerobic Digester

Q. I am looking for information on the potential impacts of a discharge of a large slug of Emulsified oil from a metal working plant into an anerobic sludge digester of a municipal WWTP.

A. My first suggestion is to get more specific information on the emulsifiers and the oil (possibly from the manufacturer) including quantifying the BOD/COD, volumetric flow rate of the "large slug" of emulsified oils and details on any potential toxicity or non-biodegradabilty of the emulsifiers or oils. Getting the toxicity and BOD/COD data will require careful, planned sampling and lab analysis to determine if there is any potential toxicity in the slug load of emulsified oil.

Then I would compare it to the manufacturers BOD/COD design rate capacity of the anaerobic sludge digester. If there is no toxicity in the emulsified oil and if the anaerobic sludge digester can meet the BOD/COD load demands of the slug loads, then it should be OK. That said, it is typically Taboo to try and handle slug loads in any treatment system. It is always better to install equalization holding tanks to capture the slug loads at the source, and then to slowly bleed the load into the treatment system. The slow feed allows the treatment system community (the eco system of bugs treating the waste) time to adapt to the new food source. The slower the feed, the better. Lastly, since the discharger is a metal working plant you should be concerned about and you should check for potential toxic heavy metals in the emulsified oil before considering discharging to the municipal system.

Regards,

Mike McGinness