anyone familiar with COD, BOD5, and OD?

anyone can tell me the difference between those and just explain it to me in simple terms. I alrdy googled it, and they always give some sort of scientific definiton..

anyone?

Not really my area of education, but this is my understanding of it...

BOD and COD are both means of measuring the amount of organic compounds in water.

BOD is a measure of the the amount of organic compounds within a sample that can be oxidized by organisms. (Or how much oxygen is needed by the organisms to "eat" the organic pollutants)
COD is a measure of all organic compounds within a sample that can be oxidized by organisms or other means. (Or how much oxygen is needed to "eat" the organic pollutants)

COD is will never be less than BOD, as it measures everything that can be oxidized by organisms (BOD) and other means.

OD = Oxygen Demand, amount of oxygen needed to oxidize all organic compounds in the sample.

I beleive BOD5 is just performing a BOD test over a period of 5 days.

This post was edited by RzChaos on Apr 2 2016 09:17pm

so what are organic pollutants? and where does "shit/fieces" come into play?

we are talkin about waste water

A carbon containing compound that has an undesired effect on the water/ecosystem.

"Shit/Feces" contains toxic bacteria that is harmful to aquatic life/other types of life, so it is a pollutant.

This post was edited by RzChaos on Apr 2 2016 10:32pm

so do we want more COD/BOD or less?

Less.

A high BOD/COD would indicate a large amount of organic matter, and would result in the depeltion of dissolved oxygen in the water. The depletion of the oxygen could have a negative affect on the aerobic marine life.

so DO is also food for the fishes ?

and DO for the bacteria is measured by BOD?

also wat is DO_saturation? is that like maximum DO at w/e degrees?

DO is dissolved oxygen. Fish need oxygen to breathe, it isn't "food". It is oxygen, just like it is for you and me.

For a given temperature and pressure, only so much oxygen can be dissolved in a sample of water.
DO_saturation would be given as a percent, like 50%. Meaning that if at the given conditions, the sample could contain a max of X DO, then it contains 0.5X.

BOD is how much of the DO is needed by aerobic bacteria to break down organic material in the water.

If you have a large amount of organics in the water, then the BOD is going to be high, because the bacteria are going to need a lot of DO to break down the material. They are now consuming a large amount of the DO, so there is less DO for other aerobic life forms.