My homemade reedbed water harvesting project
|Project:||Grey water reclamation at home|
|Client:||Me / Planet Earth|
|Cost / Value:||“Undisclosed”|
|Programme:||Spring 2006 – Spring 2007|
|Client’s Requirements:||How to beat the hosepipe ban and save the planet|
|The inspiration and research:||Article on Monday, 13 March 2006|
Article on Monday, 13 March 2006, extracted from BBC News.
Britain's biggest water company will ban hosepipes and sprinklers from next month, the firm has announced. Thames Water, whose eight million customers will be affected by the ban, says two unusually dry winters have caused "serious" water shortages. The South East has experienced its driest period for more than 80 years
I used the water usage calculator on the BBC website and estimated that my family uses approximately 400lts of water per day. That equates to 133lts per person which compares favourably to the national average of 155lts per day. Of this about 60% is for showers and baths. However, the above calculation did not include the irrigation system that I have in the garden. I recalculated the water usage including use of a hosepipe to water the garden, but for a reduced time to account for the difference between a hose pipe and irrigation system rate of flow. This added 90 lts per day. Coincidently the water used for showers and baths equates to 80 lts per day.
We already did some water conservation by collecting rain water using a single water butt and leaving the grass to grow a little longer, and not watering it. So it seemed a simple solution to use the bath waste water to water the garden. At this point I should have just decided to have showers with the plug in and siphon out the water with a hose after it had cooled. As sane people eventually did. You can even now buy special products specifically designed to make it easier.
However, I decided to research the possibility of creating a grey water reclamation system using reed beds. The local library proved, yet again, to be a good source of information, as did the internet. I learnt,
- that different reeds deal with different pollutants and pathogens,
- about aerobic and anaerobic digestion
- micro-organisms, bacteria, fungi, and protozoa
- surface or subsurface, horizontal or vertical flow configuration
- rainfall patterns throughout the year
- rate of flow through reed beds
- and area of reed bed required per person
- Pollutants and pathogens are removed from the waste water flowing through a reed bed by a complex variety of physical, chemical and biological processes, including aerobic and anaerobic microbial activity, nitrification, plant uptake, sedimentation, precipitation and filtration.
- Reed beds are successfully and economically used in full scale black water sewage treatment and industrial effluent treatment.
Importantly reed beds require little maintenance, no additional chemicals, little or no energy dependent upon the site geography / topography and are of course, completely natural.
I wanted the system to be low maintenance and durable. It also had to be aesthetically pleasing, sustainable and capable of providing adequate clean water supplies during the increased period of drought that may be experienced due to global warming. The site is relatively flat with only a slight fall towards the top of Figure 1 ‘The Site before start’ below. To minimise the energy requirement of the system as much as possible, it had to be gravity fed. However, it ultimately had to be landscaped into the garden so some pumping was going to be necessary.
The previous research indicated the there were two basic configurations, surface and sub-surface flow, with the later being further divided into, horizontal flow and vertical flow. The sub-surface configuration is thought to be better for temperate climates, especially during winter, as the water flows through the substrate, thereby staying warmer and more efficient. To have a sub-surface vertical flow configuration would involve having outlets at the bottom of the tubs, which would necessarily involve burying pipe work, access chambers and making holes in the bottom of an otherwise water tight vessel. It would also require a relatively complex distribution system for the grey water. A sub-surface horizontal system has similar difficulties with respect to the outlet but without the inlet difficulties. I considered that the sub-surface configuration imported too much risk of failure overtime and the buried pipe work and access chambers unnecessarily complicated for the relatively small gains offered by sub-surface flow configuration compared to surface flow. The surface flow configuration has the water flow above the substrate, through the reeds, and is more similar to natural wetlands. The reduced efficiency during winter can be countered by having a larger area, together with the ability to switch to normal direct discharge into the sewers if required. Therefore the surface flow configuration was adopted.
I also considered having all of the main tubs at exactly the same level so as to provide the infinity pool type look, but decided that this was impracticable, and less attractive than gently flowing water from one tub to the next, until quietly disappearing underground.
Another significant design criteria was that the system had to be operational, at least in part, in the shortest possible time and preferably before the hose pipe ban came into force. The project was therefore done in distinct phases.
The photograph Figure 1 ‘The Site before start’ below, shows the hose pipe being put to good use, marking out the edge of the development. Several shapes and locations within the garden were considered using this technique. This is the final location but not the ultimate layout. This also represents the ‘before’ photo.
Figure 1 ‘The Site before start’
The location needed to be relatively close to the house for piping the waste water from the bathroom to the surge tank. It is necessary to have a surge tank to capture a bath full of waste water, and then to allow it to flow at a regulated speed through the system so as to allow the natural processing to take place. Consideration also had to be given for the wellbeing of the plants, such that they would not always be in the shadow of the house.
The bird feeder would have to be relocated. There would be a significant loss of grass and the washing line capacity would be reduced.
Another consideration was what to do with the excavated material. I did not want the normal hole and hill, nor did I want to have to cart the material off site. Adjacent to the site, also near the house, there is an old brick built shed.
The solution adopted was to increase the thermal mass and insulation of the shed by creating a turf wall near the shed and back filling the intervening space with the sub-soil excavated. The topsoil was stockpiled for use elsewhere in the garden. The shed wall was protected with two layers of waterproof membrane to avoid damp penetration. In turn the waterproof membrane was protected by reused expanded cardboard to reduce the risk of puncture by broken flints, primarily during construction and settlement. This additional wall also incorporated an old fashioned cistern arrangement which captures all of the rain water from the shed into open water. This overflows into the reed bed system.
It is planned that eventually the shed will also be re-roofed with a living roof. Combined this will provide a much reduced visual impact to the shed together with the benefits of a larger planted area.
The pumps necessary for irrigation circulation and to lift the reclaimed water from the sump pump chamber, the lowest part of the system, to the water storage are electric. In addition to this there is a small 12v fountain in the lowest tub, which now contains fish, and a pump to power the waterfall. Both the waterfall and the fountain are primarily for aesthetics, visual and sound, but they also provide additional aeration and agitation as a by-product. The electricity for the pumps is generally provided by two 18w photoelectric panels feeding a 12v 110Ah deep cycle leisure battery. The 12v supply from the battery is converted to the required 240v by a Sterling 600W inverter. The sump pump has to be connected to the mains to avoid the continuous use of electricity required by the standing current of the inverter if it was left on all of the time. The sump pump operates automatically by float switch which activates as soon as the sump pump chamber nears capacity and therefore requires a constant supply. The electrical requirement for the sump pump is however offset by the reduction in both the water requirement and the sewerage processing, which are intensive power consumers. Hence, despite not being fully power self sufficient, it is better than carbon neutral, it has reduced our overall carbon footprint.
The rate of flow required through the system has to be slow enough to process the water but not so slow for the water to become stagnant. It also has to be fast enough to deal with the input of grey water on a daily basis and ultimately to provide sufficient surplus to provide adequate stored water for later use. The research revealed that 1-2 square metres of reed beds are required per person to process black water but not the rate of flow through the system for grey water.
The solution was to experiment within phase one of the project.
As previously stated, pollutants and pathogens are removed from the waste water flowing through a reed bed by a complex variety of physical, chemical and biological processes, including aerobic and anaerobic microbial activity, nitrification, plant uptake, sedimentation, precipitation and filtration
The waste water treatment is outlined below;
- suspended solids settle to the bottom in still water or are filtered by the substrates and plants
- organic material is broken down by microbes that live on the roots and rhizomes
- nitrates can be taken up by the plants, or they can be transformed by denitrifying bacteria to nitrogen gas
- ammonia is transformed by bacteria to nitrates
- phosphorus precipitates with calcium, iron and aluminium compounds and is subsequently removed by sedimentation and absorption to the soil and by plant uptake
- metals and toxic chemicals are removed by oxidation, precipitation and plant uptake
- pathogens die off in inhospitable environment and are ingested by other organisms, or are killed off by antibacterial compounds.
The desktop research indicated which plants would be suitable in terms of their ability to deal with different pollutants and pathogens and to process the grey / black waste water. The environment required to carry out the water treatment outlined above could be achieved within a small site with careful design, construction and selection of plants.
Additional requirements that I wanted included, that the mixed varieties should be aesthetically pleasing, readily available, manageable, some flowering, indigenous, generally of UK origin and hardy. Such a mix of plants would inevitably have different size, spread and rates of growth. One of the listed plants is bulrushes. If they were not constrained they would quickly overrun most of the other plants. The use of separate tubs, and careful selection of which plants share tubs should eradicate this problem.
In conclusion this has been a very rewarding project involving a number of different ‘green’ techniques to provide a solution to a specific problem. Albeit that this problem has yet to occur this year, the system is still working very well, producing crystal clear water day after day, whatever the weather. I have not had the water tested to be able to categorically state its quality, but suspect that it is actually potable. I believe that it has significantly reduced the family’s carbon footprint and provided interest and ongoing enjoyment.
I have added two narrow water butts at the front of the house to capture rainfall from those elevations. The water butts are small and relatively unobtrusive. It is however sufficient to be a surge tank and to accommodate the build-up during downpours which is free to flow via a garden hosepipe to the reed beds in the back garden, after keeping back enough in the second tub to water the pots in the front garden. The rain water flush provide by the front water butt and the brick shed cistern also reduce the systems maintenance requirement.
Another development to be considered is the adaptation of the WC supply to be both mains and reclaimed water. This would further reduce our mains water consumption.
Finally my thanks to the books and internet articles that provided the invaluable reference material that made this project possible.
- Transfer from old site to this one
- Photos re-mastered
- Some additional photos, Figure numbers with sufix.
- Minor text corrections
- Added tabs to aid reading
- Incorporated this article inside another