WASTEWATER GARDENS®
  Constructed Wetlands              


Humedales Artificiales
    (WWG)

JARDINES DEPURADORES DE AGUAS RESIDUALES

          JARDIN D'EPURATION DES EAUX USEES

Zones Humides Artificielles
 Schools
 Escuelas
 Ecoles
Hotel & Restaurants 
Hoteles & Restaurantes 
Hôtels & Restaurants 
Public parks 
Parques públicos 
Parcs publics 
 Homes
 Residencias
 Résidences
 Office buildings 
 Oficinas 
 Public centersBureaux 
 Centros públicos 
 Centres publics 
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Overview
Introduction - understanding sewage water
The Technology & Legal Compliance
Water Treatment Levels & Treated Water Usage
Sound Economics of WWG - Using WWG as economic incentives
Advantages of WWG: an ideal solution
Important Design Factors and Maintenance
 
Construction and installation Process
Our commitment & expertise
Presentation of the Planetary Coral Reef Foundation (PCRF)
What people say about WWG
Project references

Overview downloads

Photos and applicability in...
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Scientific Papers
 
 
Resources about constructed wetlands
 
 

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IMPORTANT DESIGN FACTORS


Climate and regional applicability

Since WWG systems rely primarely on green plants and microbes, they perform more rapidly in warm, sunny conditions, the approach is ideal for climates ranging from tropical to semi-Mediterranean-type climates and some southern hemisphere semi-desert and desert climates. In these conditions with higher temperatures and increased sunlight, system productivity is high year-round. Applications for colder regions however can also be very effective as has been shown in WWG projects in New Mexico and Poland, located in high elevation sites with long winters. However, in colder climates, the necessary surface the same amount of wastewater must be larger (at least twice than for a warmer climate) to accomplish similar treatment. Wastewater Gardens are not only especially recommended for use in on-site systems, close to the facilities they are to service, but have also demonstrated their responsiveness in areas with groundwater close to the surface, for sites with rocky or impermeable clay soils (that often prevent standard leachfields from operating), as well as for sensitive areas close to rivers, lakes and coastal waters (possible creation of buffer zones).

Greywater treatment

Greywater refers to wastewater other than that from the toilet (including sometimes toilet lavabo) refered to as faecal or blackwater. Greywater includes showers and bath water, laundry machines, sinks and kitchen water (although in some applications kitchen water can be joined to the faecal water and be treated by a WWG unit as well, as it contains food particles, grease and oil). Some water issued from industrial operations can also be classified as greywater although the water content would be carefully analysed in order to adapt the constructed wetland's design to purify ecologically harmful and sometimes synthetic compounds.
In numerous situations however, greywater doesn't call for a treatment as intensive as what is provided by a constructed wetland / WWG unit and so the WWG unit is used just to treat the black water. If land is not an issue though and that there is a large quantity of graywater to be treated, then a constructed wetland / WWG unit is also appropriate and will generally represent much smaller surfaces than if it was treating blackwater.
In the case where both types of water are separated, keeping WWG systems for blackwater treatment only, greywater would only need to pass through a sedimentation tank before going directly into subsurface irrigation trenches. The advantages of separating greywater is that more irrigation can be accomplished with the wastewater and overall project costs will be lower, as the WWG unit will treat a smaller quantity of water. However, we often work in situations where the separation between black and grey waters is too difficult and/or expensive, just as a "retrofit" to existing plumbing, and therefore design the WWG system to treat both types of water.

Stormwater treatment

In urban settings and in regions subject to flooding during storms, constructed wetlands are being employed to clean the water and to slow down the movement of water which creates flood pulses. Stormwater from urban and paved surfaces often contain pollutants like oil and fuel residues which can be readily cleansed in a wetland. In addition, in areas where freshwater supplies are limited or expensive, making use of the stormwater enables the greening of the landscape using a natural and renewable resource.


Space requirements

In the Western-type housing sector for example, we assume normal wastewater generation of 125-200 litres per person per day (European average) although this number can vary greatly according to cultural norms, geographical location and type of infrastructures and appliances (in the USA for example average amount of wastewater per day per person can be as high as 500 Liters); for example, a city dweller will have the tendency to use more water than a countryside dweller and a hotel guest for example can have a water consumption that is double or triple than a resident's. For a generation of 150 Liters of both blackwater and greywater mixed, depending on the climate and requirements of purification, we would apply a surface of 2.5 to 4 m2 of WWG surface of horizontal flow design. This indication depends on many factors including the climate (the warmer the climate, the smaller an area is needed since the plants and microbes are more effective year-round), the kind of infrastructure and water faucets used, the amount and nature of wastewater generated, what standard of treatment is required or desired. In cold climates, these numbers may be twice or three times as large, depending on the level of treatment required during the cold periods of the year when plants are dormant and bacterial activity is slower.
In the industrial sector, no pre-indication can be given as WWG surface will depend on the nature of the industry and thus on the type of compounds to be treated in the water.

Maintenance

Our representatives and designers provides detailed on-site training of indicated person or personnel and a maintenance manual upon completion of the project. Proper functioning of the systems is dependent on several simple but important principal maintenance steps are:
  • Primary treatment: septic tanks or similar systems need normal maintenance, with a final filter at the end of the primary treatment (before the water enters the WWG unit); depending on the nature of the filter used (local natural fibers or prefabricated) it will need checking every one to six months and washing/rinsing/or change of material if necessary. In the case where the primary treatment is a septic tank, itshould be pumped out when solids fill more than half its depth (in the case of a septic tank, a standard requirement for its maintenance).

  • Gravel: the surface of the gravel should be kept as clean as possible; if porosity of the original gravel declines, new gravel can be substituted or the original gravel removed and cleaned. The plants can then be transplanted back in, and the system can continue effective treatment for decades more.

  • WWG Water Level: Water levels in the wetland cells need to be checked periodically via the control box, especially during periods of low occupation when evapotranspiration may exceed input into the treatment wetland. Until plants become well established it is important that water levels not be allowed to drop below their root zone.

  • Plants: the wetland plants need normal garden care - pruning for appearance and encouragement of new growth and flowers. Heavy prunings of plants should be removed from the WWG to prevent reduction of gravel porosity when that material decays. The prunings can be used for mulch outside the system or added to compost piles. Should the WWG be planted before being used and connected to the primary treatment (septic tank or similar), in absence of the sewage water's nutrients it may be necessary to fertilize the wetland to help the plants get established (not forgetting an adequate water levels).

  • Drainage: ensuring that drainage is adequate around the WWG so that runoff rainwater and soil do not wash into the system is extremely important. Wastewater Gardens® systems are built with a berm higher than surrounding ground level, but one must check occasionally to make sure soil has not built up around the WWG basin, which would allow rain runoff and soil to enter. In the case of the drainage of treated water, if drainage into the soil is chosen, flushing of the drain pipes may be necessary to avoid clogging.