Docstoc

Sewage Treatment

Document Sample
Sewage Treatment Powered By Docstoc
					Sewage Treatment
    What’s In Sewage?

     Brainstorm a List
  Comes from sinks, toilets,
shower, bathtub in your house
      What’s In Sewage?
 Water
 Urine
 Feces
 Toiletpaper
 Tampons
 Soap
 Food Wastes
 Oil and Grease
 Bacteria and viruses
Now Add Materials in
   Storm Drain

  They are the drains in
 the curbs on the street
Wastewater from Storm Drains
 Water
 Dirt
 Water
 Oil
 Fertilizers
 Pesticides
 Grass   clippings
Now Add Industrial Wastewater

  Toxicchemicals
  Organic wastes
  Heavy metals
Where Does It Go?
Small Scale – Septic Tanks
           Septic Tanks
 Sewage    and wastewater
  pumped into settling tank
 Grease and oil rises to top
 Solids fall to bottom and are
  decomposed
 Partially treated wastewater
  discharged into drainage field
 Soil and bacteria partially filter it
Large Scale – Sewage
   Treatment Plant
How Do We Filter and
     Treat It?
        Basic Processes
 Physical/Mechanical    – removes
  large substances like trash, rocks,
  sand, tampons, etc.
 Biological – decomposes organic
  matter such as feces, food scraps,
  grass clippings, toilet paper
 Chemical – kills bacteria and some
  viruses and tries to remove nitrates,
  phosphates, heavy metals, toxic
  chemicals, etc
Steps to Sewage
   Treatment
         3 Major Steps
 Primary
  – Mostly mechanical
  – Removes big stuff
 Secondary
  – Physical and biological
  – Decompose organic matter
 Tertiary
  – Mostly chemical and physical
  – Kills pathogens
  – Tries to remove toxic chemicals
      Primary Treatment
 Influentsewage water strained
  to remove large objects such as
  rocks, sticks, tampons, etc.
 Physically done with
  mechanical rake bar screen
 Solids collected in a dumpster
  and are sent to the landfill
Mechanical Rake Bar Screen
 Primary Sewage Treatment
 Alsousually includes a sand or grit
  chamber
 Wastewater passed through
  chamber at highly controlled speed
 Sand and grit settle out
 Other wastes remain suspended
 Sand and grit sent to landfill
Sand/Grit Chamber
Residue Trucked to Landfill
   Primary Sedimentation
 Sewage    moves from grit
  chamber to sedimentation tank
 Sludge settles to the bottom
 Oil and grease rise to top and
  are skimmed off
 Produces homogeneous liquid
  for biological decomposition
 Sludge treated separately
Settling tanks have mechanical
 scrapers that push sludge into
        storage hoppers
     Secondary Treatment
 Goal  is to degrade organic matter
  such as feces, food scraps, grass
  clippings, toilet paper, etc.
 Based on aerobic cellular
  respiration by bacteria
 Held in large aeration tanks full of
  bacteria
 Bacteria “eat” organic matter for
  energy
 Use oxygen to decompose it
Aeration Chamber
Secondary Sedimentation/Clarifier

 Final step in secondary treatment
 Settle out biological floc or filter
  material
 Remaining water contains very low
  levels of organic material and
  suspended matter
 Sludge sent to drying bed
     Tertiary Treatment
 Uses  a variety of chemical,
  biological and physical
  processes to further upgrade
  water quality before release
 Not always required
Tertiary Treatment Methods
 Send  filtrate over activated carbon
  to remove toxins
 Use ponds or lagoons with plants
  and fish to remove fine particulates
 Use bacteria to remove nitrogen
  (remember nitrogen cycle)
 Remove phosphorus
Tertiary Treatment Methods
 Disinfectionto remove
  microorganisms such as bacteria,
  protozoans, viruses
  – Traditional method is the addition of
    chlorine but can precipitate out of
    solution and become carcinogenic
  – U.V. light treatment
  – Ozone treatment
 What do you do with the
        sludge?
 Most    often sent to landfill
 Can be composed and used as
  “fertilizer” in agricultural use
 Very rich in nutrients
 Could contain toxins and would
  then leach into groundwater
  and be incorporated into crops
Using Wetlandsfor
Sewage Treatment
     Using Wetlands for
     Sewage Treatment
 Use  natural or man-made
  wetlands
 Costs half of conventional
  methods
 Provides quality wildlife habitat
 Let’s nature do the recycling
   Wetland Sewage Treatment
 1st  sewage goes to settling
  tanks to remove big stuff
 Liquid pumped to oxidation
  ponds for bacterial
  decomposition
 Water released to marshes
 Plants and bacteria finish
  filtration and cleansing
 Clean water released into river

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:5
posted:12/21/2011
language:
pages:34