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

by Mike McGinness, EcoShield Environmental Systems, Inc.
June, 2010

BOD & COD Reduction Methods

Q. I hope that this will find you in good health. We operate a fruit farm. We want to reduce our waste water values of COD & BOD. I need your help because it seems that you have a lot of experience about it. We want to know the simplest, easiest and cost effective method to reduce these values.

Current values are BOD = 150 ppm and COD = 400 ppm we want to reduce BOD to below 80 and COD below 150.

Your cooperation will be highly appreciated.

A. There is little I can do long distance with so little information, except to suggest some ideas.

But it would help first if I knew more about what the source of pollution is in the waste water, is it mostly fruit, high sugar content for instance?

I have found that the biggest problem with high sugar waste water is the bacteria make too much acetic acid (vinegar), even in anaerobic (little to no O2 in the water) conditions, and the bacteria waste product (conversion of sugar to vinegar) drops the pH of the waste water, and thus stops or slows the process of BOD and COD reduction. I have used conventional pH control systems feeding a strong base to maintain the pH at near 7.5 and found that with a good air supply of small air bubbles that I could get a ten fold increase in the rate of BOD and COD reduction, as well as 98% reductions in the BOD and COD. I typically used a sand filter with a periodic back wash as a final step to remove bio solids.

Sincerely,

Mike McGinness