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Greywater Strategies

A primer on greywater recycling systems.


September 13, 2011
By Kevin Wong

Topics

In the water well world, drillers are faced with the challenge of supplying the quantity and quality of water to a home or business every day. Sometimes the well just does not produce enough. What if the well could produce 40 to 60 per cent less and still meet the needs of the homeowner? Herein lie some of the benefits of a water recycling system using greywater.

In the water well world, drillers are faced with the challenge of supplying the quantity and quality of water to a home or business every day. Sometimes the well just does not produce enough. What if the well could produce 40 to 60 per cent less and still meet the needs of the homeowner? Herein lie some of the benefits of a water recycling system using greywater.

Greywater is any household waste water with the exception of waste water from the toilet or kitchen sink, which is known as black water. Typically, 50 to 80 per cent of household waste water is greywater from dishwashers, bathroom sinks, tubs and showers.

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Freshly generated greywater is inherently not as much of a concern for treatment as black water, but if it’s not handled properly it can soon become a problem. Greywater decomposes at a much faster rate than black water. If stored even for as little as 24 hours, the bacteria in it uses up all the oxygen and the greywater becomes anaerobic and turns septic. After this point it is more like black water (a health hazard).

Traditionally, many jurisdictions have strict regulations about disposal of grey water. Some even require it to be treated as black water. Both are introduced to the sewer system for municipal disposal (or into the onsite septic system).

The benefits of reusing water
Reduce freshwater demand: When the weather is warm, about half of the water consumed by the average household in North America is for outdoor use. Capturing the indoor greywater for use outdoors can cut water usage in half.

Non-potable applications of fresh water include toilet flushing. Reused water can be used for this, thus decreasing the freshwater demand of the home or facility.

Recharge ground water: Greywater recycling for irrigation replenishes ground water, helping the natural hydrologic cycle to keep functioning.

Reduce strain on septic system or treatment plant: Greywater makes up the majority of the household wastewater stream, so diverting it from the septic system extends the life and capacity of the system. As a note of concern, “super” concentrating the black water into the septic system may call for future design changes and adjustments to the codes. For municipal systems, decreased input means more effective treatment coupled with cost savings. For onsite septic systems, this may mean lowered hydraulic loading on septic systems that are trending towards oversizing and managing the total discharges from the home.

Develop otherwise unsuitable real estate: A greywater recycling system can enable the development of land that is unsuitable for a properly sized septic system. In areas with shallow topsoil layers or not enough space for a properly sized area bed, the use of a greywater system could allow for the option by cutting down on the total wastewater discharge from the facility.

Support plant growth: Greywater can support plant growth in areas that might not otherwise have enough water.

Maintain soil fertility: The nutrients in the greywater are broken down by bacteria in the soil and made available to plants. This helps to maintain soil fertility.

Enhance water quality: The quality of ground water and surface waters is much better preserved by the natural purification processes the greywater undergoes in the top layers of the soil than by any engineered water treatment.

Greywater applications
Currently Health Canada’s guidelines for Domestic Reclaimed Water for Use in Toilet and Urinal Flushing and the National Plumbing Code reference to CSA B128 detail the acceptable uses and application of reclaimed greywater to toilet and urinal flushing and subsurface irrigation.

Onsite reclaimed or greywater systems include the collection and treatment of bath, laundry, and wash basin waste water from domestic dwellings for working, non-potable uses such as toilet and urinal flushing, and subsurface or drip irrigation.  However, the presence of pathogenic micro-organisms (bacteria, protozoa and viruses) and some chemicals in residential waste water may pose a health risk if this water is improperly treated or if it is used for other purposes.

Elements of a greywater recycling system
Greywater source(s): Washing machine, shower, bathtub and/or sinks.

Collection plumbing: Pipes that transport greywater inside the house to a storage area (for irrigation) or to a treatment system (for treatment and use for flushing).

Surge/storage tank, filter and pump: Optional elements that add complexity and cost but make the distribution plumbing’s job easier.

Make-up water: In low flow times, the greywater stored may be supplemented by potable water for irrigation or flushing. The potable water line must be protected from cross-connection for both in-house consumption issues and off-premises backflow contamination risks.

Distribution plumbing: Pipes that transport greywater from the system to locations throughout the receiving toilets or irrigation system. This part of the system should be marked with purple pipe and all outlets labelled to reduce risk of accidental consumption.

Toilets and urinals: Standard or low flow flush versions of the typical CSA B45 certified products.

Receiving landscape: Soil, roots, plants, and mulch basins that contain, cover, purify and use the greywater.

There’s one part we definitely mustn’t overlook, and that’s the people: those who design, make and maintain the system, generate the greywater, tend the garden and eat the food it produces. People are a critical but often overlooked component of the system.

The Future
Greywater recycling systems are here to stay. Leaders across the country are working furiously to integrate this new option into codes and policies to offer clear guidance for users. Future developments in policy will include guidance and policy on treatment strategies, cross-connection protections and rainwater harvesting. Some of these aspects are already being developed into some Provinces’ policies. Provincial leaders on the topic include British Columbia, Alberta, Manitoba, Ontario and New Brunswick.


Kevin Wong is the executive director of the Canadian Water Quality Association.