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<center><BIG> This page is still under construction by [[User:Lonny|Lonny]], please check back in December 09 for more accurate info.  If you are experienced in constructed wetlands, please feel free to add stuff here.  Thank you.</BIG></center>
<center><BIG> This page is still under construction by [[User:Lonny|Lonny]], please check back in May 10 for more accurate info.  If you are experienced in constructed wetlands, please feel free to add stuff here.  Thank you.</BIG></center>


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Revision as of 19:08, 14 January 2010

This page is still under construction by Lonny, please check back in May 10 for more accurate info. If you are experienced in constructed wetlands, please feel free to add stuff here. Thank you.

Greywater

Describe greywater briefly... make sure to mention alternative names grey water, gray water, graywater.

Subsurface wetland

Put a description here.

Components

Plumbing

Greywater and sewer valves underneath the Occidental greywater house.

The plumbing system is very dependent on your needs and existing plumbing system. Many possibilities exist, such as just capturing the plumbing from the bathroom sink. Another good option for capturing a lot of your water is dual plumbing to capture the greywater but allow for a valve to run greywater to sewer if needed.

Slope

Piping with a slope of 1/4" fall per foot pf run at the Occidental greywater house.

Standards require that any pipe diameter less than or equal to 2” have a slope of 1/4” fall/foot run. And any pipe diameter greater than or equal to 3” have a slope of 1/8” fall/foot run.[verification needed]

Surge tank

The surge tank is some volume to accommodate for high flow, such as times when everyone is showering and washing at once. This is necessary because the back pressure of a subsurface system is relatively high and, therefore, will slow down the flow of water. The piping to the greywater system will provide some surge capacitance, but you risk backing up into the house. You do not want to risk backing up into the house.

Primary treatment

Primary treatment of filtering solids and trapping grease is important in maintaining an efficient subsurface flow, constructed wetland for treating greywater. It is possible to combine the filter, grease trap and settling tank into one system. Each part serves a different purpose and has different maintenance needs.

Filter

A filter keeps chunks of organic matter out of the constructed wetland by directly filtering it out.
These organic chunks can clog the wetland, if allowed to enter. In addition they have very a high BOD.
Filters often need to be cleaned weekly or as needed. Build the filter so that it is easy to remove.

Grease trap

A grease trap keeps grease and fat from getting into the constructed wetland, by providing a barrier to floating material.
Grease and fat can coat surfaces in the constructed wetland and greatly reduce the treatment capacity of the system, if allowed into the wetland.
The grease trap should be skimmed weekly or as needed. It will start to look nasty quickly.

Settling tank

A settling tank allows for smaller particles to settle out before entering the wetland, by providing some time of slow water velocity.
These smaller particles can slowly clog the entrance of the system, if allowed to pass through the pretreatment.
The settling tank should be inspected weekly and cleaned every few months or as needed.

Subsurface constructed wetland

Building a subsurface constructed wetland consists of making a volume that is about 1 meter deep, putting in some baffles, filling it with gravel and planting it with wetland plants.

Hole

The size of your hole should be sufficient to treat the greywater. See System Sizing for more.

Pond liner

The pond liner protects the groundwater from contamination and may not be necessary in locations with low percolation, clay soils.

Baffles

The baffles protect the system from short circuiting, i.e. water finding a quick route from the entrance to the outtake.

Gravel

The gravel makes sure that the system remains subsurface, providing more treatment area (on the surface of the rocks), reducing the attraction to vectors and protecting from accidental contact with humans.

Plants

Cattails
The plants should be local wetland plants. Such as:
  • Brass Button
  • Bulrush
  • Broadleaf Cattail
  • Common Mare’s-tail
  • Common Rush
  • Cordgrass
  • Duckweed
  • Jaumea
  • Marsh Pennywort
  • Marsh Rosemary
  • Pickleweed
  • Saltbrush
  • Sea-Arrow-grass
  • Umbrella sedge
  • Water Parsley
  • Water Plantain

To find local wetland plants. Seek out low lying wet areas. In dry climates this may be near a factory, business or residence with a semi-constant effluent stream.

Outtake

System Sizing

Many variables effect the sizing of a constructed wetland greywater treatment system. For instance, high temperatures make for faster processing, high BOD needs longer retention time, surface use of effluent needs longer retention time, etc. Likewise, there are many ways to size a system. In the opinion of Lonny, sizing a system based upon retention time is misleading, as treatment effectiveness varies with type of system and environment. Instead rules of thumb can be used. Alternatively, BOD and hydraulic loading calculations can be used much as they are to size municipal wastewater treatment marshes. This method can be adapted to small scale greywater.

Rules of Thumb

Some simple rules of thumb can make system sizing a very brief procedure.

  • According to Oasis Designs: 1/2 to 1 square foot of subsurface wetland for every gallon of greywater per day
  • According to the Humanure Handbook 1 of Constructed Wetland for every 1 gallon of graywater per day.

To make these rules of thumbs match - Humanure handbook must be referring to a maximum two foot depth.

So, for a system for 150 gallons/day of greywater would need a constructed wetland system with a 75 to 150 square foot footprint.

BOD loading

Steps to determining sizing based upon BOD loading:

  1. Determine BOD of influent (mg/l convert to lb/gal)
  2. Reduce that BOD for primary treatment (%)
  3. Determine greywater daily flow rate (gal/day)
  4. Use wetland treatment ability (45 lb/acre*day)[verification needed] see this doc to find a value
  5. Calculate the size of your system.

So, for a system with with 150 gallons per day of greywater at 100 mg/l BOD and a primary treatment BOD reduction of 40%:

BOD * reduction percent for primary treatment
100 mg/l * .6 = 60 mg/l
BOD in mg/l converted to lb/gal
50 mg/l * 8.35x10-6 (l*lb)/(mg*gal) = 5.01x10-4 lb/gal
Flow rate * BOD * Treatment
[150 gal/day * 5.01x10-4 lb/gal] / [45 lb/(acre*day)] = .001669 acre
Convert acre to square feet
.001669 acre * 43,560 ft/acre = 72.7 square feet

The fact that this number is lower than the 75 square feet calculated by the rules of thumb, is probably due to primary treatment that is not included in the Oasis Design figures.

Caveats

  • Do not use an in sink food disposal (aka garbage disposal)
  • Use Garden friendly soaps (no borax, etc.)
  • more

Final Images

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