BOD, COD, TDS, TSS! What does it all mean? Here are some metrics and explanations… Just so we’re clear.
To set things straight, some definitions:
BOD = Biochemical oxygen demand
COD = Chemical oxygen demand
BOD is generally 60% of COD for brewery wastewater
TSS = Total suspended solids
TDS = Total dissolved solids
Pounds of (BOD/COD/TSS) per day =
(8.34*(BOD/COD/TSS in mg/L)*gallons)/1,000,000
Example: 10,000 gallons of 5,000 BOD wastewater equals
= 417 pounds of BOD
Is your brewery metric? Even easier (of course)
kg of (BOD/COD/TSS) per day =
((BOD/COD/TSS in mg/L)*m3 of wastewater)/1,000
Example: 40 m3 of 5,000 BOD wastewater equals
= 200 kg of BOD per day
This 417 pounds of BOD is referred to as load, on a daily basis it’s the loading rate. You may need to know how to calculate this for limits or surcharges your municipality wants to enforce.
Pounds per day of BOD? Load. What the heck does that mean?
Imagine you have a keg of beer you need to dump. You can dump it down the drain as is; or you can dump it in to 1,000 gals of water, and dump all of that down the drain. The volume is very different, the concentration is very different, but the load is the same. It’s still pollution that the local wastewater plant needs to remove.
Is dilution really the solution to pollution?
BOD is a 5-day test, COD is a 2 hour test. For this reason alone it is better to be regulated by COD instead of BOD. There are other advantages to COD as well, and this is certainly worth negotiating if your public works starts talking BOD.
*The following numbers are averages and will vary quite a bit (better yet, look at this blog entry)
Expected COD of full strength wastewater without sidestreaming: 13,000 mg/L
Expected COD is low strength wastewater after sidestreaming: 3,000 mg/L
Expected COD of the concentrated sidestream source: 64,000 mg/L
Expected TSS of low strength wastewater after sidestreaming: 500mg/L
For reference, typical household wastewater has a COD of about 400 mg/L, commercial wastewater (laundries, restaurants, grocers) COD varies quite a bit, but 500 to 1,000 mg/L is a good range.