Water Treatment

- sewage was initially dumped directly into rivers

- problem: waste water upstream is someone’s drinking water downstream

- eventually, people built sewer systems to take sewage to the ocean. We thought this wouldn’t be a problem because the ocean is so large.

- fish and plants die

- food chain is affected

- health risks for humans

- loses recreational value

- e.g., uptown Saint John, Meenan’s Cove beach

Treating Water

1.       Primary Treatment - physical separation of large items

2.       Secondary Treatment

          A.      Activated sludge

                    a.       waste water is pumped to large tanks

                    b.       air is pumped in to help growth of bacteria which decompose the solids

                    c.       after several hours, the water is pumped to a settling tank where some solids settle to the bottom and is called “sludge”

                    d.       some of the sludge is returned to the first tank so the bacteria can keep growing

                    e.       this process removes 90% of the organic waste

3.       Sludge Digester

          A.      sludge is held in the tank for 15-20 days

          B.      bacteria that don’t need oxygen continue breaking down the organic matter. The activity produces heat which speeds up the process.

          C.      Methane is a waste product which could be used as an energy source

4.       Sludge disposal. Sludge can be

          A.      incinerated for energy

          B.      used as fertilizer

          C.      composted using worms and other decomposers

          D.      safely handled because disease organisms are killed by heat

5.       Disinfection of water

          A.      use chlorine to kill microbes after secondary treatment

          B.      if any organics are still present, chemicals called trihalomethanes (THM) are formed. They have been shown to cause cancer

          C.      can also use ozone (O₃) or ultraviolet light (UV) to sterilize

6.       Alternatives

          A.      Wetlands - can be used to treat water naturally. Need a lot of space so can’t always be used in cities.

          B.      Lagoons - large pools where air is bubbled into the water to speed up decomposition

          C.      Aquaculture - waste water can be used to grow shellfish. They filter impurities out of the water.

          D.      Septic tank - mostly used in rural areas or suburbs because requires space for the septic field

7.       How do we get “more” water?

          A.      better treatment

          B.      use less water by conserving

          C.      reduce waste by repairing leaks

          D.      desalinate (take the salt out of) ocean water