Liquid Waste Management

Wastewater

Liquid waste, often but not necessarily containing water, is called wastewater

Sources of Liquid Waste

• Municipalities (houses, businesses, institutions): from sinks, tubs, showers, toilets

• Agricultural activities: rainfall and irrigation runoff from farms contains fertilizer, pesticides, manure, and soil; runoff from ranches and feedlots contains nutrients, organic matter, bacteria, growth hormones, and drugs

• Industry: Industrial wastewater may contain petroleum products, metals, acids and other chemicals, nutrients, and sediments

Municipal Wastewater

Municipal wastewater is divided into two types:

1) Storm water

2) Sewage

Storm Water

• Includes rain and melting snow that run off roads, driveways, roofs and lawns into storm sewers.

• May contain sediments, organic matter, and chemicals.

• It often runs directly into water systems.

Connected or Separate?

• In many Canadian cities, storm water sewers are connected to sanitary sewers, and all this water is treated. Heavy rains may overload the system, causing raw sewage to back up into houses and natural waterways.

• Having separate storm and sanitary sewers prevents this problem. However, storm water flowing into natural waterways can:- erode stream banks- increase the temperature of the receiving water, reducing available oxygen- introduce chemicals that can harm aquatic life.

Sewage

• Material that is rinsed down the drain or flushed down a toilet into the sewage system.

• Contains wash water (showers, baths, laundry, dishes) and organic matter, like food particles, urine, and feces.

• Also contains hundreds of chemicals, including: plasticizers, medicines, pesticides, flame retardants

Sewage Treatment

• Liquids cannot be disposed of in a landfill because they increase leaching and destabilize the landfill structure

• Sewage must be treated before the water it contains can be returned to the natural system

Septic Systems

• 14% of Canadian homes are on a septic system• Wastewater drains into a septic tank. Grease and oils

rise to the top, solids sink to the bottom• Clarified liquid waste runs from the tank through pipes

embedded in gravel below the soil surface of the septic field

• The pipes have small holes, allowing water to drain into the gravel and soil, from which it leaches or evaporates

• The tank must be pumped out occasionally

Municipal Sewage Treatment

Sanitary sewers take municipal sewage to a water treatment plant.

1. Primary Treatment

• Primary treatment removes solids and suspended sediments

• First, a screen removes large debris

• In a grit tank, heavier particles like sand and gravel settle out

• In a primary sedimentation tank, about half the organic solids settle to the bottom. This semi-solid material is called sludge.

2. Secondary Treatment

Secondary treatment breaks down the organic material biologically in one of the following ways:

1) Aeration tank digestion: sewage is aerated and mixed with aerobic bacteria, which digest the organic matter. The sewage then goes into a final settling tank, and the sludge is removed.

2) Trickling filter bed: Sewage drips from perforated pipes or overhead sprayer through a stone bed or corrugated plastic sheets. Bacteria on the bed decompose the organic material.

3) Sewage lagoon: Outdoor lagoons expose sewage to sunlight, algae and air, which break down the organic material (a slower but cheaper method)

After secondary treatment, the fluid is disinfected with chlorine, UV light, or ozone to kill harmful bacteria.

3. Tertiary Treatment

• After secondary treatment, sewage still contains nitrates, phosphates, and other inorganic substances.

• It is passed through a natural wetland or artificial filtering system to filter out these nutrients, or chemical flocculants are added to bind to the nutrients so they settle out.

https://www.youtube.com/watch?v=oaXth88i7rk