Biological oxygen demand (BOD) also biochemical oxygen demand is a measure of dissolved oxygen required by anaerobic organism in oxidation of organic matter in a given water sample. It is an indicator of the putrescible organic matter available in water. A low (BOD) implies good quality if water, while on the other hand, a high BOD is an indicator of polluted water.

Organisms such as bacteria, algae, and any aquatic habitats are responsible for consumption of dissolved oxygen(which is the amount of oxygen available in water in dissolved form). When dissolved oxygen drops below a certain level, life does not continue normally. The drop in D.O level in water has a negative impact on the aquatic life. This can be caused by weed invasion and growth, fish and other aquatic life kills, and more so, the introduction of foreign sewage effluents by humans. Energy is consumed in the oxidation process of all these, where oxygen is a core part of this process.

The main sources of BOD include woody debris, topsoil, leaves, animal manure, effluents from paper mills and pulp, feedlots, wastewater treatment plants, urban storm water runoff, food processing plants and failing septic systems. BOD is directly affected by the same factors affecting dissolved oxygen. To measure BOD, two measurements are taken, first, an initial measurement of the dissolved oxygen is taken right after the sample id taken. The second is incubated for 5 days in the lab, having been optimized for thriving of microorganisms and then tested to get the final dissolved oxygen level. This value is used to determine the amount of oxygen used up during the five days. This test is a bio-assay procedure aimed at showing the amount of oxygen consumed by aquatic habitants while they utilize organic matter available in wastes under nature replicated conditions. In order to acquire accurate results, great care needs to be applied to avoid say, introduction of additional air. Temperature is maintained at 20C since it’s the usual temperature of bodies living under water. This is also good at maintaining an optimal temperature value.

Biological oxygen demand (BOD) is an important water quality parameter since it provides a standard index to measure the effect discharged wastewater will impact on the receiving environment. A higher BOD value implies a greater amount of organic food at the disposal of oxygen consuming bacteria. Dramatic depletion of oxygen can lead to anoxic or hypoxia environments.

BOD is extensively used for wastewater treatment, this is because decomposition of organic wastes by microbial is commonly used for the treatment. Regulation of BOD varies from region to region and from country to country. Generally, the maximum allowable concentration level for the direct discharge to the environment fall around 10 mg/L BOD, while the allowable maximum concentration for discharge into the sewer system is usually 300 mg/L BOD. These values are helpful in ensuring that any company discharging its wastewater effluents does not affect the aquatic life negatively in a great way. This is meant to ensure that aquatic life is preserved and maintained thus longevity.