Proposed grey water system for Sunflower Cohousing

Grey water treatment Having recently purchased Chris Stewart’s sequel to ‘Driving over lemons’, I was drawn to the following extract (courtesy of his publisher, ‘Sort of Books’) with respect to his ‘Eco Folly’, which epitomises, far more eloquently than I could ever hope to achieve, my current thoughts as to a possible grey water treatment process:

He (Trev) imagined our eco-sphere (for swimming) as a pool of crystalline water, filtered by secondary pools filled with a cleansing jungle of lilies, reeds, rushes and water-mints. Schools of delicious fish, later to be harvested for the household, would cruise to and fro devouring the organisms and micro-organisms inimical to the purity of our pond. A great bolster of raw untreated sheep’s wool would float upon the surface of the reed-pool to suck up all the gunk that fouled the water from sunburn oil and other unguents. And any organism or clod of muck that escaped this formidable net was to be lofted by a solar-powered waterwheel up to an immense stone bottle filled with selected sands and sifted earths from long before the dawn of man. From the great bottle the filtered water would meander along stone runnels where the action of the sun’s rays upon the thinly spread flow would knock any surviving bacteria on the head. Then the pure water would cascade over a fall of sun-baked stones back into the main pool. The whole was to be constructed using natural and locally-occurring materials; the shapes were to be organic and uplifting; the landscaping with stone and plants indigenous and exotic; and the project could be completed with an unpretentious pavilion of pisé and thatch. I have recently re-considered my own thoughts as to our proposals for waste water treatment as of necessity. In advance of an open day planned for summer 2016, where I wanted to promote the water treatment proposals, I arranged for three trial holes to be excavated in the area at the base of the adjoining field, where we were intending to create a rainwater collection pond and reed-bed. Two of those holes revealed compacted sand, and, whilst the third trial hole did expose some grey clay, none of the trial holes would retain water. I also had discussions with the machine operator, and later with a stonemason who we had employed to build a fireplace and chimney breast, and who has had very similar experiences in life, and has a very similar outlook. The consensus was that, owing to the hot, dry summers in this area of France, the evaporation rate, coupled with the lack of rainwater run-off, would mean that our proposed collection pond would simply dry up despite the grey water feed even if we managed to resolve the water retention issues.

I also feel that the provision of a vinyl pond liner as an alternative would not be very eco-friendly, whilst the cost would make a serious dent in finances. The second event which has caused me to re-think, is that our swimming pool, which has largely been abandoned since we moved in, developed a leak, and we wanted to consider alternative possible uses for this area.

Diagram of a typical domestic grey water reed-bed system

Many grey water treatment systems have been developed for third world countries, with the systems basically comprising settlement and surge tanks, followed by progressively smaller stone and sand particle filters. If one also wants to include murky grey water including kitchen scraps, then one of the settlement tanks would need to be a septic tank, for anaerobic treatment of settled sludge. The treated water is only intended for crop irrigation, and it is only more recently that systems have incorporated reed beds and aerobic treatment to try and improve the water quality. I would like to take these processes a stage further and incorporate simple commercially available filters in order to remove particles at an early stage in lieu of settlement tanks, and to take on board techniques used in the DIY Koi carp industry, particularly ‘trickle filtration’ and ‘protein skimmers’. I would also like to adapt and improve upon these methods and incorporate additional treatment using fish. We also need to consider whether our existing swimming pool could be utilised/adapted/re-built as this fish pond, with any surplus water being pumped to the potager for watering of vegetables, or whether we might want to retain a swimming pool, and build a new fish pond in-between the existing sand filter bed and the swimming pool.

System design principles

1. Biological The ethical setup of our community requires that the grey water treatment system should have a small carbon footprint. This will rule out the use of chemicals, and my current proposal is to instead use inline sieves and particle filters followed by reeds and other aquatic plants, in conjunction with fish, to treat the water. Removal of suspended solids is important since

suspended solids comprise the majority of the biological oxygen demand (BOD). The BOD not removed by the particulate filtration system must be removed by the biofilter before effective ammonia removal will occur (ammonia + nitrogen (from the air) = nitrates, then nitrites, which are fed upon by the fish). Thus the size of the biofilter is influenced by the effectiveness of the particulate filtration system. If the fish don't have oxygen you are out of business no matter what else you do. Aeration is always the first step when increasing the oxygen carrying capacity over an open, lightly loaded system. Mechanical surface aerators, subsurface air bubblers and pure oxygen injection is the typical progression in terms of technology and complexity. All aerobic biofilters require oxygen to operate. If the biofilter does not provide its own oxygen, it will be limited to the oxygen carried in the water. The quality of the water as it enters the system, and the quality of the water required as a finished product, will have a profound effect upon the nature and sizing of the treatment process. Water from the kitchen sink will have an initial higher degree of contamination because of food waste, and many greywater systems avoid the collection of such water in order to keep the system as simple as possible.

Term Definition Other terms in use

Greywater Untreated household wastewater that has not come into contact with sewage

Graywater, gray water, or grey water

Black water Wastewater from toilets, bidet, water used to wash diapers (and under some definitions, from kitchens (WHO‐ROEM 2006))

Sewage

Dark greywater

Untreated household wastewater that has not come into contact with sewage, but is from lower‐quality sources such as kitchen sinks and dishwashers

(Sometimes considered to be part of black water)

Greywater Source Possible Contents

Automatic clothes washer

Suspended solids (dirt, lint), organic material, oil and grease, sodium, nitrates and phosphates (from detergent), increased salinity and pH, bleach

Automatic dishwasher

Organic material and suspended solids (from food), bacteria, increased salinity and pH, fat, oil and grease, detergent

Bathtub and shower

Bacteria, hair, organic material and suspended solids (skin, particles, lint), oil and grease, soap and detergent residue

Sinks, including kitchen

Bacteria, organic matter and suspended solids (food particles), fat, oil and grease, soap and detergent residue

Source: WHO‐ROEM 2006

The composition of greywater strongly depends on the behavior of the inhabitants and the individual choice of soaps and detergents in the household. Therefore, the overdosing of shampoos and detergents as well as the use of strong detergents (e.g. with high sodium content, phosphate content or chlorine) should be avoided. One of the questions which needs to be asked is whether we should separate the black water, and the more initially highly contaminated dark grey water, from the water from bathroom sinks, showers and baths. If so, are we then to simply to ignore the former water sources as a potential source of recycled water (for whatever use, and again, we could possibly have a tiered system of potential uses linked to the initial contamination levels)? There is already a substantial sand filter bed (of relatively recent origin) located in the courtyard which is used to treat the effluent from the existing ‘toutes-eaux’ collection tank as part of the traditional French ‘fosse septique’ arrangements serving the existing house and, we could, without too much difficulty, arrange for the more highly contaminated dark grey water, and the ‘blackish’ water, to continue to pass into this latter filter bed. The downside of this proposal (in addition to providing two separate systems) is that this potential source of water will be lost. The alternative is to deliberately design and provide a more sophisticated water treatment system which can deal with all three sources of water. 2. Cleaning and maintenance The system needs to have low long-term maintenance requirements – this will be substantially assisted by having good access to early stages of the filtration system such that these can be disassembled and cleaned in order to remove larger particles. The way that solids are removed is also important. The best systems remove solids quickly without degrading them in any way. If the solid particles are broken or reduced in size, it makes it easier for nutrients to dissolve into the water. These nutrients must then be removed by another part of the water treatment system or flushed out by water exchange – as such, it is better if these particles can be physically removed by way of regular, planned maintenance. Time is also important because the longer solids are held in the system, the more degradation will occur. Floating bead filters are particularly bad in this regard since they hold the solids for long periods of time before backflushing.

3. Gravity If we are to avoid the use of pumps as far as practicable, the system needs to be gravity fed where possible. The dwellings have been deliberately designed to have their kitchens, and as such, the start of the grey water system, facing onto the central courtyard. Grey water from the bathrooms is also directed to this same initial connection into the system. One of the options, and possibly one of the goals, is to use the existing swimming pool (or, at least, the locality) as either a natural swimming pool (with the grey water system biologically, instead of chemically, treating the water), or as a treatment pool, with floating beds of reeds and other aquatic plants, and also, in this latter instance at least, incorporating a fish colony as part of the treatment process. The natural fall of the land from the courtyard towards the South-East corner of the site where the swimming pool is located immediately establishes the preferred line of the treatment process. 4. Grease traps It had already been the intention to provide individual grease traps to each property before connecting into the external drainage system – these could also incorporate a first stage large particle filter (possibly simply some form of a net which can be withdrawn and cleaned on a regular basis).

Treatment technique

Description Pros Cons

Disinfection Chlorine, ozone, or ultraviolet light can all be used to disinfect greywater

Highly effective in killing bacteria if properly designed and operated, low operator skill requirement.

Chlorine and ozone can create toxic byproducts, ozone and ultraviolet can be adversely affected by variations in organic content of greywater.

Activated carbon filter

Activated carbon has been treated with oxygen to open up millions of tiny pores between the carbon atoms. This results in highly porous surfaces with areas of 300‐ 2,000 square meters per gram. These filters thus are widely used to adsorb odorous or colored substances from gases or liquids

Simple operation, activated carbon is particularly good at trapping organic chemicals, as well as inorganic compounds like chlorine.

High capital cost, many other chemicals are not attracted to carbon at all ‐‐ sodium, nitrates, etc. This means that an activated carbon filter will only remove certain impurities. It also means that, once all of the bonding sites are filled, an activated carbon filter stops working.

Sand filter Beds of sand or in some cases coarse bark or mulch which trap and adsorb contaminants as greywater flows through

Simple operation, low maintenance, low operation costs.

High capital cost, reduces pathogens but does not eliminate them, subject to clogging and flooding if overloaded.

Aerobic biological treatment

Air is bubbled to transfer oxygen from the air into the greywater. Bacteria present consume the dissolved oxygen and digest the organic contaminants, reducing the concentration of contaminants.

High degree of operations flexibility to accommodate greywater of varying qualities and quantities.

High capital cost, high operating cost, complex Operational requirements, does not remove all pathogens.

Membrane bioreactor

Uses aerobic biological treatment and filtration together to encourage consumption of organic contaminants and filtration of all pathogens.

Highly effective if designed and operated properly, high degree of operations flexibility to accommodate greywater of varying qualities and quantities.

High capital cost, high operating cost, complex operational requirements.

Common greywater treatment technologies (adapted from NovaTec Consultants Inc. 2004)

5. Progressive particulate cleaning

The main filtration system will, if we are to follow established techniques, take the form of a sand filter - bacteria, virus and phosphorus removal is enhanced when using sand rich in iron or aluminium oxides. Prior to the sand filter itself there will be a call for filters composed of larger particles (gravels), and also a call for a

surge tank in order to ensure that the sand filter is not set awash with sudden larger water volumes (possibly say from a bath being emptied). I suspect that the surge tank simply has a restricted size outlet in order to control flows.

Physical greywater treatment system used in Qebia Village, Palestine (the ‘four barrel system’)

The size of the filter depends on the greywater quantity to be treated. As general rule, the required area for a four barrel system is quoted as being 1.25 m² of filter surface per 100 L of greywater a day. To ensure proper functioning of the filter the surface should be at least 1 m² and should not exceed 2.5 m² - If the expected amount of greywater requires a bigger area, the implementation of multiple filters for independent greywater sources is understood to be recommended. We can make an assessment of our own requirements by checking on the metered water consumption, and making an allowance (25% to 50% is suggested by differing sources) for toilet flushing if this latter water is to be treated separately. One source suggests that the four barrel system is sufficient for up to 6 family members, whilst another source suggests a greywater allowance of 100 L per person per day (in the USA, or 30L per person per day in India). Remember, however, that these figures are based upon a sand filtration system in isolation, and where the treated water is intended to be of sufficient quality for crop irrigation. If we

are to incorporate additional treatment methods such as reed beds and fish pools, a much larger volume of water can be treated, producing a much improved water quality, and the recommended sizing should be mentally adjusted accordingly.

An alternative is to use a ‘confined trench’ system, which is quoted to be adequate for 240/300 litres per day. This system comprises a plastic barrel at one end of a polyethylene lined trench acting as a grease and solids trap, with water then fed into a 3 metre x 1 metre x 1 metre trench filled with gravel (a horizontal filter bed) giving a 2/4 day low level anaerobic retention period, before water filters out at high level at the far end. An adaptation of this latter technique might be to include planting to the top of the filter bed with reeds. There could also be further variations on a theme, with worms being incorporated in the upper filter layers (sand), giving an aerobic, as opposed to an anaerobic process, and thereby removing smells. Conventional on-site treatment in France means septic tanks and large sand filter beds. Since their function (except when they "back-up") is not detectable at ground level, they have been assumed to be "working". But the notion of "working" needs redefinition. The basic problem with conventional septic systems is that they introduce nutrients and microbes too deeply into the ground for any natural processes of decomposition and plant uptake to happen. In nature, almost all organic material is processed on or very near the surface by numerous macro- and micro-organisms - and plant uptake is considered by some authorities to be the last--and-crucial--stage in the recycling of these nutrients. 6. Water purifying plants (courtesy of Wikipedia)

Plants that have been used in temperate climates include Nymphea alba, Phragmites australis, Sparganium erectum, Iris pseudacorus, Schoenoplectus lacustris and Carex acutiformis. Where oxygenation is a critical requirement Stratiotes aloides, Hydrocharis morsus-ranae, Acorus calamus, Myriophyllum species and Elodea have been used.

7. Policies, regulation and religious beliefs There does not appear to be any published research associated with the use of sand filters in conjunction with either reed beds and/or fish pools, although we do know that such schemes exist (Hockerton (UK) and El Valero (Spain)) - the users are known to swim in the treated waters, and the quality of the water in both instances is reported to be above EEC requirements for bathing water, although I personally have my doubts as to whether either of these systems also treat black water. The European Council Directive 91/271/EEC states that “treated wastewater shall be reused whenever appropriate,” however, how to determine if it is appropriate is left ambiguous (Somogyi et al. 2009). At the national level, Australia has developed guidelines for greywater reuse, “Australian Guidelines for Water Recycling: Managing Health and Environmental Risks,” and reuse is encouraged. In his work on local acceptance of greywater, Laban identified four important questions people may raise regarding greywater reuse: acceptability with regard to religious and cultural values; affordability and financial benefits; difficulty; and ability to improve access to sufficient quality and quantity of water (Laban 2010). This highlights the need for a participatory approach to the development of greywater reuse technologies, so that the needs and concerns of the user are addressed. There has also been some perception that greywater reuse is not compatible with Islamic religious beliefs, although in 1978 the Council of Leading Islamic Scholars (CLIS) in Saudi Arabia found that treated wastewater can be reused as long as it does not present a health risk (Al-Jayyousi 2010 citing CLIS 1978).

Final thoughts/proposals

1. Rainwater from the West slope of the West barn should also be diverted through the system in order to dilute the ‘blackish’ water and thereby ease the treatment problems downstream. This is not to say that we should abandon the existing underground rainwater cisterne behind the East barn – this should instead form the final gravity storage facility at the end of the treatment run, and will continue to collect water from the remaining roof surfaces.

2. Stored water from the cisterne should be pumped up to high level storage tanks within the roofs of the new houses and thence fed to WC’s for flushing, to external taps for watering and, via an underground connection, to storage containers within the potager for watering of vegetables etc. If these storage containers were to be fitted with float valves, and thereby remained permanently full, we could use individually fed smaller containers in various differing locations, and there would be no need to inter-connect these containers using a ‘water-level’ system. This would also then release the existing IBC’s to be used as containers within the grey water treatment system.

3. We should make ‘free’ use of mains electricity for pumping. Instead of trying to incorporate independent solar electric stations serving smaller pumps, we should be looking to adopt a much larger scale grid-connected solar system as a separate future project.

4. We should also make use of the existing swimming pool, either as a fish pond for further treatment of the waste water, or to retain this as a natural swimming pool but also stocked with fish, possibly also with floating reed beds. If you have seen the picture in Chris Stewart’s book – ‘A parrot in the pepper tree’, I envisage a similar series of ‘artistic’ steps leading down into the pool, wrapping around the internal curvature at the far end of the pool. We could delay making a decision as to whether or not we retain this pool for swimming purposes until we have had an opportunity to assess the quality of the water following treatment.

5. We should make no attempt to use the existing sand filter bed of the ‘fosse septique’ as part of our grey water treatment system. This is an unknown quantity, and everything else touched by the previous owners has turned out to be bodged. In any event, it is highly unlikely that this bed retains water, but simply acts as vertical filter and storage vessel prior to water being adsorbed by the ground below.

6. The head of the grey water treatment system would take the form of grease traps immediately to the front of individual dwellings. These grease traps use 50mm diameter fittings, and the waste water pipework system within the dwellings is also 50mm diameter, only reducing to 40mm or 32mm at the service points (shower, basin, sink).

7. Once sufficient oxygen is provided, the next easiest way to improve water quality is to remove suspended solids. Suspended solids consist primarily of uneaten food and faeces which are slightly denser than water. Large particles, above 100 microns, will settle out quite easily. Particles above 50 microns can be filtered out with a screen. Particles below 10 microns are difficult to physically filter and would be removed by a sand filter.

8. Grease traps should be connected via larger diameter pipework fitted with integral mesh containers in order to catch larger particles. I am currently researching the possible integration of cylindrical stainless steel mesh baskets and/or cartridge filters

to be fitted inside the pipeline. These baskets and filters would need to be inspected and cleaned on a regular weekly basis.

9. The next item downstream would be a ‘surge’ tank with the latter having a small diameter outlet in order to restrict the flow of water into the treatment zone beyond. The interconnecting pipework between the early stage filters and the surge tank should be of 100mm diameter to act as an additional reservoir.

10. The ‘surge’ tank should be fitted with a large fish-tank aerator, surrounded by a large number of small bags (plastic mesh) filled with gravel. The gravel pebbles will provide a surface for micro-organisms to develop, providing a first stage treatment, whilst the use of small bags will permit these to be lifted out individually for annual cleaning. By providing vigorous aeration, in addition to oxygenation, I would hope to develop a second stage ‘bubble protein skimmer’ with any scum collecting on the surface of bubbles as a froth or foam, again to be cleaned out on a regular weekly basis.

11. A series of small diameter outlets (600mm (?)) below the top of the tank would feed into a narrow vertical reservoir filled with large car sponges, which could be removed and washed through and/or replaced on a regular basis as part of a planned maintenance program. This vertical reservoir would interconnect with a shallow horizontal reservoir at the base of a 3 metre long x 1m wide trench, and separated from a sand filter above by a geomembrane. The sand filter itself would be capped with worms and grasses as a third stage treatment. A high level outlet from the far end of the sand filter bed would lead into a vertical ‘trickle filter’, open to the atmosphere, with water trickling over gravel contained within stacking plastic boxes. These filters encourage micro-organisms to develop which purify the water, and the process also encourages further oxygenation. The trench, including the surge tank, would be surrounded by a thick polyethylene membrane in order to retain the water within the confines of the trench.

12. We will need to retain vehicular access to the far side of the East barn – as such, the connection from the base of the trickle filter would be connected underground into the wall of the swimming pool above water level. This end of the pool, behind stone filled gabions, would be provided with vertical baffles hung in a spiral fashion in order to extend the length of the process path, and would also be provided with floating reed beds. Water would then be pumped back up from the far end of the swimming pool to the surge tank in order to repeat the cleansing process. Excess water from the swimming pool would drain from the far end of the swimming pool via the existing skimmer and an underground connection to the underground ‘cisterne’ before being pumped back up to the high level storage tanks within the roof space of the new houses for re-use for flushing WC’s and watering of the potager.