COD

Chemical Oxygen Demand, or COD, measures the quantity of oxygen required for chemical oxidation of organic and inorganic substances in a sample of water. It is measured by mg/l of O². It gives and indication of the total amount of organic and inorganic substances and therefore of human contamination.
This parameter attests the potential level of pollution in waterways and in sewage. A high reading of COD in drains involves a reduction of dissolved oxygen in the water and also determines a reduced power of self-purification as well as the possibility to sustain aquatic organisms.

BOD5

Biochemical Oxygen Demand, BOD, is an important parameter used to evaluate the amount of pollutants in water. It measures the quantity of oxygen consumed by microorganisms for biochemical oxidation of some substances in a standard time: 5 days.
It is similar to the process that occurs naturally in waterways or in biological depuration plants by means of bacterial flora which uses up dissolved oxygen to oxidize and depurate the pollutants.
Three types of substances are tested:
Type A: organic compounds that are used by microorganisms as nourishment.
Type B: oxidable compounds of nitrogen, derived from nitrites, ammonia and organic nitrogenous substances that are used as source of energy by specific bacteria (nitrobacteria and nitrosomonas).
Type C: substances that can be only chemically oxidized, such as iron, sulphides, etc. These substances can be analyzed by COD.