Sewage

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.

Treating Sewage: A Costly Proposition
Conventional sewage treatment is an expensive process that uses a lot of energy. During periods of heavy use or rapid growth, increases in wastewater volume add to that expense. As a taxpayer, you may be asked to fund short-term measures to cope with temporary crises, or to approve longer-term capital outlays for upgrades to your community's sewage system and treatment plant.

Besides wastewater from sewage, there is urban runoff: water that flows down streets and into storm drains. In some coastal communities, urban runoff flows untreated into the ocean. When this happens, the runoff also transports contaminants such as gasoline, oil, paint, heavy metals, pesticides, human and animal waste, and trash. These contaminants pose a severe threat to the ocean as an economic, recreational, and biological resource as well as to the community's residents and economy.

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