Permaculture sewage treatment – first aid and future proofing for our rivers and seas
by Féidhlim Harty
Given our love of conversation about the weather, we're never happier than when there's a big storm brewing on the Atlantic and pushing our way. Now that we've taken on the North American convention of naming our storms after innocent bystanders (rather than climate deniers), we can begin to pinpoint exactly who is to blame as we bandy about our latest climate dramas. It's a bit like a game of Cluedo: “I accuse Ophelia in the hay barn with the broken roof tile!”
Well actually, it wasn't in the hay barn, nor with a broken roof tile. But Ophelia is guilty for something alright. The recent storms downed electricity lines around Ireland and the UK. One of the impacts was an interruption to sewage treatment systems. So what? Not as important as missing the Sunday game, you may argue. Well, for the fish, aquatic insects, birdlife, animals and people living downstream of malfunctioning sewage treatment systems it can be quite serious indeed. Life or death in some cases.
If we want to create sustainable, healthy systems to support us, we cannot rely on such a fickle friend as fossil energy for electricity generation to keep our sewage treatment systems running smoothly. Quite apart from the increasing potential for power cuts in a changing world, when conventional sewage infrastructure “runs smoothly” it is still heavily reliant on the constant use of electricity to convert biomass and nutrients into somewhat less polluting effluent before disposing to our rivers and coastal waters. Clearly in a world desperately in need of solutions that work, this needs to change.
So what would permaculture sewage treatment look like? Some permaculture principles to consider in this context may include: “produce no waste”, “each important function must be supported by many elements” and “use and value renewable resources and services”. The first principle here immediately points to a challenge in the very terminology we use. Sewage is a waste, de facto.
A good place to start may be in redefining the challenge and not referring to sewage treatment at all, but instead to sanitation. Sewage treatment is inherently focused on minimising the problem, whereas when we look at the opportunities inherent in a redesign of our sanitation infrastructure “we are surrounded by insurmountable opportunities” to quote Bill Mollison.
Solutions in brief
Dry toilets are the obvious place to start this discussion. Well designed, built and maintained, dry toilet systems can be easy and pleasant to use and can produce high quality humanure compost for use in the garden or farm.
There are a number of different categories that we can used to classify dry toilet systems, listed in Fig. 1, but the notable similarity is that the system is used without water (or very little water in the case of microflush systems) and the output is generally rich compost, in due course.
The main advantages of dry toilets are the elimination of black water (water from a flush toilet) and thus a great reduction in the potential for groundwater or surface water pollution. Also, conservation of water is another significant advantage, saving about 40% on the average home water use (the remaining 60% is from grey water – from sinks, washing machines, baths showers etc.).
Compost toilet duly installed, we still need to turn around and address the pollution potential of our grey water. In the past, this used to be plumbed to a soak pit in the garden, but we now know that they merely introduce the grey water deep in the ground, within or close to the groundwater and permit little or no filtration. Possibly the most eco-friendly grey water system is to recycle it to a polytunnel for irrigation.
Be careful with your shopping basket though. Every bar of soap, bottle of shampoo, chemical cleaner under the kitchen sink or even the washings from art projects etc. will end up in your vegetable patch. You can limit this by syphoning out bath water only and allowing the rest to flow to a separate system.
A reed bed or wetland system is an excellent solution for dealing with grey water (or with all the sewage if you decide that actually you'd prefer a flush toilet). There three basic types of treatment wetland, as follows:
Soil based constructed wetlands (or Free Water Surface wetlands, Wetland Ecosystem Treatment systems - WETs, or Integrated Constructed Wetlands – ICWs). These most closely resemble natural marshes, with about 10cm of water sitting on a soil base.
The water is filtered as it passes through the leaf litter and plant stems and interacts with the roots and soil media in the wetland basin.
Plants used include common reed (Phragmites australis), bulrush (Typha latifolia), yellow flag (Iris pseudacorus), water mint (Mentha aquatica) and other species. (c.100m2 for a domestic system prior to percolation, to produce the same effluent quality as a standard mechanical treatment system.)
Horizontal flow gravel reed beds (or horizontal sub surface flow systems). These are usually 60-70cm deep with a planted medium of gravel through which the effluent passes. The plant diversity is typically more limited, with common reed predominating and sometimes yellow flag and water mint added for some diversity. (c.50m2 for a domestic system.)
Vertical flow reed beds are typically pump fed systems of sand and gravel-filled basins. Note that gravity distribution systems may also be used where falls allow. Syphon systems or dosing boxes are the most common gravity methods of spreading the effluent effectively across the surface of the bed.
Common reed is the typical plant used, with water mint and yellow flag for colour. (c.5-15m2 for a domestic system – may be split into two basins in series. VF reed beds are often used as the first stage in a multi-stage system, often followed by a horizontal flow reed bed to get the effluent cleaner again.)
If you want to have a flush toilet then the above reed bed sizes are the ones to adopt in order to get “secondary” treated effluent (where primary treatment is simply settlement in a septic tank). Tertiary treatment is cleaner again, and typically needs an extra reed bed sized at 10-50% of the first bed. The effluent should be routed to an infiltration area for additional treatment in the soil and disposal into the groundwater.
Another option that would qualify for inclusion in the Permaculture Top Ten is a willow system
There are willow filters, which can be used after a septic tank or reed bed in the place of an infiltration area. These allow willows to feed on the nutrients from your effluent and in doing so help to further protect the groundwater quality.
Zero discharge willow systems are a Danish innovation that use a plastic lined basin, backfilled with soil and planted with willows for evaporating 100% of the effluent to air.
These are promoted by the Danish authorities in sites where groundwater pollution may be a problem. Willow filters and zero discharge systems both have the additional advantage that they mop up atmospheric carbon as they grow. If the wood is used for heating you can offset the fossil energy requirements for your home.
Beyond your own garden
Looking beyond our own gardens, we will also need permaculture solutions for municipal use, if we are to make the shift to healthier, more ecologically sustainable lives. In this instance, source separation systems can be retrofitted to existing flush sewer infrastructure or introduced on a phased basis, or on new-build developments.
Urinals and urine diverting toilets can both be used to collect valuable liquid fertiliser and reduce pollution. Faecal separators such as the Swedish Aquatron unit can be used to recoup humanure for composting and return to our farms to build soil humus. Municipal grey water and industrial effluents may be the least easy to recycle, but even these can be used with town-scale willow plantations to grow firewood and fuel district heating.
Whether it is first aid for our rivers and seas, or future proofing our sewage infrastructure against energy shocks, permaculture can offer many solutions for domestic and municipal sewage management. Although not something that can necessarily be achieved overnight, I can see healthy soils, rivers and people in the permaculture options mentioned above. With good design, the opportunities are truly endless.
Féidhlim Harty is an environmental consultant and writer, and director of FH Wetland Systems Ltd., a company specialising in wetland and reed bed design, willow systems and habitat enhancement. He is the author of Septic Tank Options and Alternatives and Permaculture Guide to Reed Beds, both published by Permanent Publications.