That part of precipitation, snow melt, or irrigation water that drains off land into surface water. It can carry sediments and pollutants into the receiving waters. The second step in most waste treatment systems in which bacteria consume the organic parts of the waste. It is accomplished by bringing together waste, bacteria, and oxygen in trickling filters or in the activated sludge process. This removes floating and settleable solids and about 90 percent of the oxygen-demanding substances and suspended solids.
Disinfection is the final stage of secondary treatment.
Sediments settle to the bottom of surface water. The tendency in deep water bodies for distinct layers of water to form as a result of vertical change in temperature and, therefore, in the density of water. During stratification, dissolved oxygen, nutrients, and other parameters of water chemistry do not mix well between layers, establishing chemical as well as thermal gradients. A type of wetland that is dominated by woody vegetation and that does not accumulate appreciable peat deposits. Swamps may be freshwater or saltwater and tidal or nontidal.