Sewage

Sewage We all know what we flush down the toilet or what we pour down the drain. What happens to all that stuff? In answering the above question, keep in mind the first law of thermodynamics, the bit about neither being created nor destroyed but changing from one form to another. Just because you flush it doesn’t mean that it disappears forever.

Historical Context of Sewage Important note: prior to the 1970’s most of the raw sewage, the stuff coming out of the houses, was simply dumped into the environment – usually within rivers or oceans. The book mentions that the mistreatment of sewage is one of the main instigators of the Clean Water Act (1972). The Clean Water Act (CWA) helped establish modern sewage treatment by appropriating funds to local and state governments to build or revise existing plants.

Sewage Treatment Modern Sewage Treatment = based on the filtration and biological decomposition.

Sewage Treatment The raw sewage contains at least these four components: – Debris (toilet paper, feminine products, other things that get flushed) – Particulate organic mater – Colloidal dissolved organic mater (things in solution or partial solution, like urine – Dissolved inorganic mater – Misc. Chemicals

Sewage Treatment Preliminary = the raw sewage flows out of your house to a sewer line, which eventually leads to a municipal treatment plant. In the preliminary stage the raw sewage is filtered through a 1” mesh. The solids and paper that accumulates on the mesh screen is raked off and transported to an incinerator or taken to a landfill.

Sewage Treatment Primary Stage = after passing through the preliminary filtration, the raw sewage flows to a circulation chamber. Here the sewage is slowly circulated – the change in the velocity causes the courser materials, such as grit and other bits of organics, to settle out. The stuff that settles at the bottom is referred to as sludge; it is removed and taken to a landfill by dump trucks. In addition, grease, fats, and oils will float on the surface. These fatty materials are siphoned off and merged with the sludge.

Sewage Treatment Secondary Treatment = in this stage of sewage treatment the remaining dissolved organics and nutrients are broken down via aerobic and anaerobic decomposition. The sewage is aerated with oxygen and decomposing bacteria are added. The bacteria “feed” on the organic materials left in the water and utilize the remaining nutrients.

Sewage Treatment After biological decomposition, the water is then sterilized, by either chlorine or ozone gas, or ________. Then it is released back into the environment. Usually municipal treatment facilities pump the treated sewage into a river or pump it out into the ocean. Water exiting the sewage treatment facility (gray water) in many places is cleaner than that which comes out of your tap.

Secondary Treatment

Processing of sludge

Gray Water In many cities the water exiting the sewage treatment plant is reused. Some cities use gray water to water lawns.. However in major metropolitan areas where water is scarce – the desert west – gray water might be an option for drinking water?

Septic System Waste leaving the home flows through a septic tank. In the tank the solids settle towards the bottom. Here the organics breakdown through aerobic and anaerobic decomposition. The colloidal and dissolved in-organics flow out into the yard via a drain field. The effluent is supposedly filtered naturally by the lawns, gardens, and soil microbes.

Septic Tank Problems Septic tanks have to be cleaned out about every 5 years depending on usage. If there are more solids than the system can handle, the tank will backflow and the sewage treatment becomes ineffective. Leaking septic systems, or poorly working ones, can leak too much raw sewage into the environment. If too much water passes through the septic system, it will turn the yard all mushy. 

Septic Tank Problems Also if there are too many septic systems built within too small of an area, the sewage will not be properly filtered or broken down. The excess nutrients and organics will contaminate the groundwater.

Sewage Ponds Many newer communities are using sewage ponds to treat their waste. The sewage ponds also employ biological decomposition. In this case the raw sewage is pumped into a containing pond. The solids accumulate at the bottom of the pond. The organic materials are feasted on by decomposers. Aquatic vegetation is also planted. The vegetation uses theorganics and nutrients as fertilizers.

Clean Water Act 1972 The Clean Water Act is the sister of the Clean Air Act. It was the first legislation of its kind to protect the Nation’s waters and to create safe drinking water. During the Environmental Movement there was a push to clean up polluted water.

Clean Water Act This was in large part due to: – Accumulating sewage – Factory effluents (discharge) from the Chemical Revolution – People getting sick from polluted water (see the movie A Civil Action). – The Cuyahoga River caught fire in 1967

Clean Water Act 1972 The Clean Water Act: –Gave the EPA the power to set regulations on sewage effluent –Appropriated funds to local governments to retool poorly working sewage treatment – Gave power to the EPA to regulate the amount of pollutants emitted by factories – Protected the US waterways (“Navigable Waterways”). Under this definition wetlands are designated “navigable waterways”, and the CWA gave power to the Army Corp of Engineers to protect wetlands.

Clean Water Act 1972 The Safe Drinking Water Act 1974 (from the same vein as the CWA) authorized EPA to regulate the quality of public drinking water and to set drinking water standards