Organisms Used in Water Purification - Organisms

Organisms

Saprophytic bacteria convert dissolved organic impurities into living cell mass, carbon dioxide and water. These saprophytic bacteria may then be eaten by flagellates and ciliates which also consume suspended organic particles including viruses and pathogenic bacteria. Clarity of the water may begin to improve as the protozoa are subsequently consumed by rotifers and cladocera. Purifying bacteria, protozoa, and rotifers must either be mixed throughout the water or have the water circulated past them to be effective. Sewage treatment plants mix these organisms as activated sludge or circulate water past organisms living on trickling filters or rotating biological contactors.

Aquatic vegetation may provide similar surface habitat for purifying bacteria, protozoa, and rotifers in a pond or marsh setting; although water circulation is often less effective. Plants and algae have the additional advantage of removing nutrients from the water; but those nutrients will be returned to the water when the plants die unless the plants are removed from the water. Plants also provide shade, a refuge for fish, and oxygen for aerobic bacteria. In addition, fish can limit pests such as mosquitoes. Fish and waterfowl feces return waste to the water, and their feeding habits may may increase turbidity. Cyanobacteria have the disadvantageous ability to add nutrients from the air to the water being purified.

The choice of organism depends on the local climate different species and other factors. Indigenous species usually tend to be better adapted to the local environment.