The concentration of chemicals, which is commonly reported in wastewater samples as mg/L or ppm, shows the volume of a substance (i.e., mg of BOD) present in a known volume of wastewater (i.e., in 1 Liter).
Concentration is, therefore, a relative number and does not tell us how much there is of the chemical/substance, such as the mass or the weight that is being discharged.
The absolute number is referred to as loading. Loadings are commonly reported as kg per day (kg/d).
BOD stands for Biochemical Oxygen Demand and is defined as “the amount of dissolved oxygen needed by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period.”
Other chemical measurements include:
- COD (Chemical Oxygen Demand)
- TOC (Total Organic Carbon)
- O&G (Oil and Grease)
To show the scale of the chemical concentration, it is valuable to state what the measurements of these chemicals are in a healthy body of water.
There are 4 main categories to measure wastewater quality:
1 - Organics
"A determination of the concentration of carbon-based (i.e., organic) compounds aimed at establishing the relative 'strength' of wastewater."
Biochemical Oxygen Demand (BOD)
Chemical Oxygen Demand (COD)
Total Organic Carbon (TOC)
Oil and Grease (O&G)
2 - Solids
"A measurement of the concentration of particulate solids that can dissolve or suspend in wastewater."
Total Solids (TS)
Total Suspended Solids (TSS)
Total Dissolved Solids (TDS)
Total Volatile Solids (TVS)
Total Fixed Solids (TFS)
3 - Nutrients
"A measurement of the concentration of targeted nutrients that can contribute to the acceleration of eutrophication."
4 - Physical Properties and Other Impact Parameters
"Analytical tests designed to measure a varied group of constituents directly impact wastewater treatability."