Before thinking about ways that you can conserve and recycle water in your household, it is necessary to understand the different household wastewater streams and terminology.
Wastewater streams can be classified into 3 main types:
- Storm water – water that runs off from roofs and other surfaces (such as roads) into drains and eventually into streams and rivers and out to the sea.
- Grey water – water from showering/bathing, washing clothes, handwashing basins, washing dishes etc.
- Black water – water containing urine and sewage and anything else that goes down the toilet
Water is technically a renewable resource because it is recycled in different states around the globe through the hydrological cycle, which is powered by the sun. However, in some contexts, it is being used and polluted faster than it is being returned to the cycle or cleaned. This means that water is becoming an increasingly scarce resource around the world.
The availability of water around the globe depends on several factors:
- The amount of precipitation the area receives
- The latitude (distance from the equator)
- Soil type (ability to hold ground water)
- Vegetation type
Based on these factors, and then weighing them in relation to the human needs for water, regions around the world either face a water scarcity, shortage or surplus depending on the time of year.
Treatment and re-use of wastewater
Recycling storm water can be problematic because of all the toxins it can contain from the surfaces it runs on. Generally, it is not recommended that storm water be recycled. The best we can do is manage what it contains and try to filter it before it goes into the surrounding ecosystems. Storm water can contain all kinds of toxins, such as oil and fuel residues, as well as chemicals such as paint, paint thinners, particles of rubber and plastics (from car tires) and a range of other petrochemicals typically used with cars.
The natural principles of slow, spread and sink are relevant here – first ensure that storm water flow speed is slowed, to reduce its erosion potential (and the nuisance and danger this poses), then spread it across large surface areas (and filter it eg. With sand and gravel) before allowing it to sink into wetlands or streams. Managing storm water quality is a significant way that you can improve the condition of ecosystems where you live.
Recycling of grey water
Water use in a household depends on the income and standard of living / income level of the household. Generally, about 60% to 70% of household wastewater in homes in the USA and other high-income countries is grey water. Depending on lifestyles, this amount can vary from about 20 to 45 gallons per person per day. Most of this comes from washing clothes and bathing.
What does greywater contain?
- Detergents and Soaps;
- Blood (menstruation and injuries eg. Shaving);
- Hair and body tissue (skin fragments, skin cells etc);
- Fats (from soaps);
- Phosphates from soaps – this is what makes them foam;
- Due to detergent soaps, the pH will be high (it will be alkaline rather than acidic);
- This high pH means only certain plants will survive / tolerate the greywater;
- Phosphates can be considered as both the ‘contaminants’ in the water and the food source for the good bacteria that work in breaking down / decontaminating greywater.
What are the main steps for treating and re-using greywater?
Greywater re-use systems can be very simple.
Here are a few key steps to follow in greywater re-use:
- Make sure the greywater and blackwater do not mix;
- Allow the greywater to be stored so it can settle out the solids and fats (fats and any solids to sit on the top of the water);
- Anaerobic treatment (bacteria);
- Aerobic treatment (bacteria);
- Pumping or flow onto plants / garden.
How can grey water be recycled?
Here are some simple principles to follow for reusing your household greywater:
- Use grey water either for irrigation in the garden or it can be filtered and re-used for flushing toilets;
- Use a a kind of fat trap to collect fats and oils from washing dishes. This could be a simple sponge which is washed regularly;
- Mix grey water with rainwater if possible (eg. Connecting gutters from your roof) as this helps to dilute the wastes in grey water;
- Follow nature’s water management principles – remember the three S’s – Slow, Spread and Sink (first slow the flow rate of the water down, then spread it across a large surface area and store it in a system, and allow it to sink into its natural filtration system);
- Aim to replicate ecosystems – especially if we are ensuring our own survival – allowing nature to continue with the ecosystem services that we rely upon;
- Use cheap and easily available technology;
- Choose a level of system that works for your budget (no need for expensive pumps or filters);
- Base your system design on the amount of space you have available (to store greywater for settling);
- Allow the grey water to get in contact with the roots of the plant you wish to grow, not the leaves or fruit eg. Trees, bushes, shrubs, flowers
- Be careful of heavy metals from grey water accumulating in the plants – this is not likely if you are healthy and use good quality water – but it’s always good to do regular water tests;
- Pay attention – do regular maintenance of your system – to stop it clogging up for example. The settling tank for greywater should have the floating waste solids (fats / scum and sediments) pumped out of it regularly.
What can a grey water recycling system look like?
- A simple system where water from the bathroom is sieved to catch large particles, and then connected via pipes to a hose in the garden outside;
- Grey water can be sieved and piped outside into a storage container where it can settle, and where the scum can be separated. This can then be pumped out for the garden or back into the toilet flushing system;
- A more complicated system would involve sieving greywater and allowing it to seep into constructed wetlands (with layers of gravel and sand and stone, or small plastic wheels as a surface area for bacteria to live on) with water loving plants such as reeds. This encourages bacteria to process the wastes, and the cleaned water at the bottom can be captured in a pipe, stored and re-used.
What plants can be grown using grey water?
- The easiest option here is to find out about and grow plants which can tolerate the conditions of the water coming out of your household system – without having to treat the water to make it cleaner, using an expensive series of tanks and pumps;
- Grey water should not be used to water soft leafy vegetables like spinach, and generally not for any vegetables at all. Rather use greywater for decorative plants or for plants which are not consumed by humans or animals;
- Do not use grey water to water anything that you will consume that will be in direct contact with the water.
Illustrations of ideas for a home grey water recycling system
Here are some ideas for simple domestic grey water systems.
Illustration courtesy of P Pacey
Reuse of black water
Black water can be reused if it goes through a carefully designed system involving anaerobic (without oxygen) and aerobic (with oxygen) bio-digestion. This is where solid and liquid wastes are decomposed by certain ‘good’ bacteria that use the wastes as food.
The resulting solid waste can be used as a fertilizer, and the liquid waste water that comes out can be used for irrigating plants that are not consumed, for example, lawns on golf courses. Sometimes this process produces methane, which can be used as a gas for cooking or heating if tapped off correctly. This recycling of black water should be done very carefully, and the output solid waste and water should be tested regularly for toxins, heavy metals and harmful bacteria.
Post contributed by Claire Mollatt
Pictures of black water system (these principles can be adapted for grey water treatment)
NOTE: Recycled black water must be tested thoroughly and black water recycling systems are usually only effective on larger scales.
Photo 1 – courtesy of Neil Padmore
Example of installation of large underground greywater storage tanks in hole. Two initial settling tanks for black water.
Photo 2 – courtesy of Neil Padmore
Example of how ground over the tank can be reinforced (to prevent soil from caving in and crushing the tank)
Photo 3 – courtesy of Neil Padmore
Example of pump / slurry pump inside tank
Photo 4 – courtesy of Neil Padmore
Rope to attach to pump so that you can pull it up for maintenance
Photo 5 – courtesy of Neil Padmore
Examples of piping, gulleys and potential location of sieves / traps for grey water exiting a bathroom
Photo 6 – courtesy of Neil Padmore
Keeping the top of the tank accessible for maintenance (Eg. pumping out scum)
Photo 7 – courtesy of Claire Mollatt
Example of media (small tubes) to be used as a surface for bacteria to grow on in a wastewater treatment system (the aerobic section) – a biofilter
Photo 8 – courtesy of Claire Mollatt
Aerator (bubble maker) for aerobic digestion / treatment of wastewater
Photo 9 – courtesy of Claire Mollatt
Example of scum on top of blackwater / greywater
Photo 10 – courtesy of Claire Mollatt
Example of how landscaping can hide tanks – a rockery
Photo 11 – courtesy of Claire Mollatt
Series of treatment tanks – anaerobic digestion of the waste water first and then aerobic (with the aerator device). Final tank has cleaned water that can be recycled as irrigation water.
With many thanks to Neil for taking time in showing and explaining his water recycling system to me.
— post contributed by Claire Mollett —