Transcript water treatment

WATER TREATMENT
Point Source of Polluted Water in
Gargas, France
Is Bottled Water the Answer?
• U.S.: some of the cleanest drinking water
• Bottled water
– Some from tap water
– 40% bacterial contamination
– Fuel cost to manufacture the plastic bottles
– Recycling of the plastic
• Growing back-to-the-tap movement
Trash Truck Disposing of Garbage
into a River in Peru
Natural Capital Degradation: Highly
Polluted River in China
Girl Sits on the Edge of a Road beside a
Stream Loaded with Raw Sewage in
Iraq
Sewage Treatment Reduces
Water Pollution (1)
• STRATEGY IS TO
REDUCE POINT
SOURCE POLLUTION
• Septic tank system
• Wastewater or sewage treatment plants
• SETTLING TANK- where grease and oil rise to
the top and sludge settles. Solids are
decomposed by bacteria. This is why, in
theory, you should not use chlorinated
cleaning products.
• DRAIN FIELD- liquid waste drain from pipes
and percolate downward filtering and allowing
bacteria to biodegrade materials
Solutions: Septic Tank System
Process of wastewater treatment
– Primary sewage treatment
• Physical process-uses large screens and a grit tank to
remove large objects and grease and allow organic
solids to settle out in the form of sludge.
Top view of Forest City Wastewater
treatment plant
•
•
•
•
1. Headworks Building
This houses a mechanical bar screen and grit/grease removal system which removes the larger
solids and readies the flow for entry into the First-Stage Aeration Basins
2. First-Stage Aeration Basins
These two basins provide an optimum oxygen supply for decomposition of the sewage by bacteria.
The flow is regularly checked for nutrients, pH, solids, pathogens, metals and organic chemicals.
The flow then enters the large Second-Stage Aeration Basin.
3. Second-Stage Aeration Basin
Here further oxygenation and decomposition occur. A complex group of micro-organisms break
down (feed on) on the suspended or dissolved organic impurities remaining in the water. No
chemicals are used throughout this decomposition process, only the natural action of many
bacterial species.
4. Clarifiers
From the big basin flow gravitates to two clarifiers, the round settling tanks. Remaining solids settle,
and most are returned back to the aeration basins at a rate of 1.3 MGD. The clear top layer in the
clarifiers is then chlorinated to destroy pathogens, then de-chlorinated with sulfur dioxide prior to
release to Second Broad River. This effluent meets or exceeds all EPA requirements for biological
oxygen demand rates.
• Secondary sewage treatment-employs aerobic
bacteria to degrade organic waste. Here further
oxygenation and decomposition occur. A complex
group of micro-organisms break down (feed on)
on the suspended or dissolved organic impurities
remaining in the water. No chemicals are used
throughout this decomposition process, only the
natural action of many bacterial species.
• Aeration- used to introduce additional oxygen
Aeration of sewage to encourage the
aerobic bacteria for decomposition
Ignaz Semmelweis
– Tertiary or advance sewage treatment
The clear top layer in the clarifiers is then
chlorinated to destroy pathogens,
• Bleaching, chlorination kills microorganisms such as
chlolera. then de-chlorinated with sulfur dioxide prior
to release to Second Broad River
• The use of filters to remove phosphates and nitrates
Sewage sludge or biosolids
Solutions: Primary and Secondary
Sewage Treatment