Sewage
Solid waste going into landfills has a serious impact on the environment, but it's not our only disposal concern. Wastewater also needs to be managed in order to reduce threats to public health, safety, and the environment. Wastewater can consist of industrial waste, human waste (or sewage), or runoff from rainwater.
All of the wastewater produced by a city eventually ends up in a river, lake, or ocean. On its way, this wastewater flows through a sewage treatment plant. In conventional sewage treatment plants, bacteria remove up to 90 percent of biodegradable organic wastes before the sewage moves to a sedimentation tank, where remaining solids and microorganisms settle as sludge. The sludge is incinerated, dumped in the ocean or a landfill, composted, or used as fertilizer. The remaining wastewater, still containing oxygen-demanding wastes, suspended solids, nitrates, phosphates, and toxic metal compounds, may pass through additional advanced sewage treatment before being discharged to the river, lake, or ocean.