The partially treated effluent from a food processing industry, containing high concentration of biodegradable organics, is being discharged into a flowing river at a point P. If the rate of degradation of the organics is higher than the rate of aeration, then dissolved oxygen of the river water will be lowest at point P.

The most important type of species involved in the degradation of organic matter in the case of activated sludge process based wastewater treatment is chemoheterotrophs.

For an effluent sample of a sewage treatment plant, the ratio BOD5-day, 20 °C upon ultimate BOD is more than 1.

A young lake characterized by low nutrient content and low plant productivity is called eutrophic lake.