Usually consists of clarification with or without chemical treatment, in most cases by settling solids and skimming. At the end of this stage, floating and settled solids have been removed and half of the metals and conventional pollutants are eliminated. It consists primarily of clarification followed by a biological process to produce sludge. The solid material which settles, or is precipitated, out of sewage during the treatment process. Below the tide line.
High turbidity reduces the penetration of light.
The water column contains dissolved and particulate matter, and provides habitat for plankton, fish and marine mammals. Microscopic animals that move passively in aquatic ecosystems.