21. Landscape Sustainability - Wastewater Reuse cont'd

I wanted to close the loop on the discussion of the sustainable use of household waste water - What can you do with the dirtier stuff that doesn’t qualify as Greywater? This is sometimes called Blackwater, the difference being where it comes from and the contaminants and pathogens it contains. Generally the wastewater from toilets is called Blackwater, all the rest are considered Greywater, but what are the specifics?

Distinguishing Grey from Black

Laundry washing machines have a little bit of grime and the remainders of detergents that can be pretty benign, and therefore can be legally diverted into the landscape without a permit in California. Water from showers, tubs, and bathroom sinks are also usually not too dirty and can be used for irrigation if approved with a permit. The kitchen sink and dishwasher might produce dirtier water depending on factors such as your diet, and there can also be a greasy component, so this wastewater is not allowed as part of a legal Greywater system. Waste from the toilet of course contains much more serious contaminants and pathogens that are hazards to human health.

The use of laundry washing machine water in the garden is clearly an easy and very advantageous thing to do, as described previously. Adding all the other sources of greywater into that landscape irrigation system can be done, but ideally you would use a more complex system than the one I described before, in order to minimize maintenance issues and maximize efficiency. In my view the ideal system for this is a Constructed Wetland.

Constructed Wetlands

A Constructed Wetland is not some giant swamp, it is simply a depression in the ground about 2 or 3 feet deep, lined with a waterproof layer, filled with gravel or sand and planted with the appropriate plants. After filtering out the solids, wastewater enters at one end and flows through the porous gravel to an outlet on the other side, getting filtered along the way. The plants are happy to take some of the “pollutants” out of the water, which are nutrients for them. Its best to research the plants well, and use ones that are particularly good for filtration and uptake, and its important to have a steady flow of water into the area to keep these plants healthy. Visible water pooling should only occur briefly when there is a lot of flow into it, you need to avoid long term standing water that allows mosquito breeding. The water that flows out of this area is then routed to mulch basins typical for a greywater system, or other forms of distribution to irrigate your yard’s plantings. With a constructed wetland you are really starting to close the loop ecologically, getting the wastewater generated on site back to the organisms that can make use of it. The hard part in many urban yards may be finding enough space in the right spot so that the natural slope works to your advantage.

Composting Toilets

That still leaves us with the toilet Blackwater to deal with. At a larger City or community scale, it is possible to take this waste into a constructed wetland, as long as there are some filtering/treatment steps taken first. A great example is the Arcata Marsh and Wildlife Sanctuary in Arcata, CA (see links below). At the residential scale, the best approach is the Composting Toilet. A composting toilet takes the waste, combines it with high-carbon materials like sawdust or wood chips, and allows it to decompose into high quality soil, a.k.a. compost. This is in fact a modern fixture that can look like a normal toilet on the surface, but has various chambers beneath the floor or in another room, a far cry from the old style outhouse. And no, it doesn’t smell bad unless it isn’t working right – it has its own vent, and by adding sawdust or other high carbon materials, and keeping it aerated, a balanced decomposition process occurs with no strong odors. There are plenty of companies selling these, and they are commonly used in off-the-grid homes, vacation properties and other such places. I’m not sure about the official regulations on using composting toilets in urban areas that have municipal sewer systems, but you can see how perfect it is for closing the loop on your household wastewater and turning it into a valuable resource.

Complete Ecologies for Wastewater Treatment

Taking the idea of closed loop ecologies even further is the idea of wastewater being treated by a complete ecosystem of plants, microorganisms, and other aquatic species like snails and fish, which can even produce food for your table! John Todd is considered a pioneer in the development of this idea, and has created the “Eco-Machine” concept that includes a fascinating complexity of life that can even clean wastewater from toxic industrial sites (see references below for links). To me, this seems ideal, drawing on the diversity of the natural world to match “waste” with the organism that can use it as a resource.

The San Francisco Public Utilities Commission has installed a similar system in their new office building, using a patented Living Machine to clean all of the building’s wastewater in street level planters. In addition to watering the building’s landscaping, some of this water is recirculated for flushing the toilets. In this case there are some stages of more traditional treatment involved, but it still saves a huge amount of water. A related concept is Aquaponics, putting fish and plants together to create a sort of balanced ecology that can sit inside your house. This has even been incorporated into artistic forms, such as the amazing “Local River” piece by the French artist Mathieu Lehanneur.

Synthesis

We’re almost through a whole list of topics related to water in the landscape and can start to think of synthesizing these concepts into a complete system of landscape design features that make use of all the rainwater and wastewater resources right on your property. The last piece of this puzzle is making the most of this water in the landscape through the use of high efficiency irrigation systems and drought tolerant plantings… coming soon!

References:

Sustainable Landscape Construction, J. William Thompson and Kim Sorvig

Gaia’s Garden – A Guide to Home Scale Permaculture, Toby Hemenway

Solar Living Sourcebook, published by Real Goods, Executive Editor John Schaeffer

San Francisco Greywater Manual for Outdoor Irrigation, sponsored by the SFPUC, downloadable at http://sfwater.org/index.aspx?page=100

Create and Oasis with Greywater, Oasis Design, www.oasisdesign.net

Legal Greywater Design for Small Scale Applications in California, published by The Water Institute at OAEC, https://oaec.org/our-work/projects-and-partnerships/water-institute/

City of Arcata wastewater treatment marsh http://www.humboldt.edu/arcatamarsh/

Sun Mar composting toilet company www.sun-mar.com

John Todd Ecological Design (Eco-Machines) https://www.toddecological.com/

Mathieu Lehanneur, artist of “Local River”  http://www.mathieulehanneur.fr/project/local-river-127