Biochemical Oxygen Demand (BOD) is the amount of oxygen required to bring about complete biochemical oxidation of organic matter. The term “decomposable” means that the organic material is utilised by bacteria as a source of food and energy.

The BOD test is the usual parameter to measure the organic pollution of domestic and industrial wastes. It provides a useful measure of the amount of oxygen which will be required if an effluent which is not fully oxidised is discharged into a watercourse where aerobic conditions exist. The BOD test therefore provides a measure of the degree of pollution in a water course which will result from addition of the effluent .

Under natural conditions organic matter is degraded by a wide range of organisms which promote oxidation of carbon to carbon dioxide, nitrogen to nitrate ion, sulphur to sulphate ion, phosphorus to phosphate ion, and so on. Hydrogen is converted to water. Inorganic materials, trace elements, etc either remain in solution (usually as the chloride) or are precipitated as a sediment, depending upon the pH of the solution.

The predominant organisms responsible for these processes are naturally present in the soil and most waterways.

What kind of transformation takes place when organic matter is subjected to biological attack? In order for the organic matter to be oxidized by bacteria it must serve as a food material from which the organisms can derive energy for growth and reproduction. This means part of the OM (organic matter) is converted to cell tissue. This part will remain unoxidized until such time as the organism must draw upon cell tissue to derive energy to maintain life.

When bacteria die they become food for other bacteria and another transformation to carbon dioxide, water and cell tissue occurs. Living and dead bacteria serve as a food source for higher organisms such as protozoans. In each transformation further oxidation occurs but in the final analysis there remains a certain amount of OM that is quite resistant to further attack. This is commonly known as humus.

The rate at which this proceeds is governed to a major extent by population numbers of organisms and the temperature. This is why BIEMS works so well, it quickly increases the number of organisms by billions and billions which then rapidly break down organic wastes. Where adequate amounts of BIEMS are used a highly significant increase in biological activity will be noticed within 24 to 96 hours. Gas bubbles will surface and settled solids will begin to break down.

After initial applications have been made to increase the biological activity, the amount of BIEMS may be reduced to a maintenance level that supplements the needs of oxygenating bacteria.

The major advantages of BIEMS are:

• Reduction of offensive odours, usually within the first 24 hours
• Accelerated decomposition of solids and release of cleaner effluent
• Significant reduction in the BOD of effluent
• Increased population of aerobic bacteria