What is a good way to dispose of grey water?

In some cases, grey water can be used to irrigate a garden. See 'Can I store and use grey water from my bathroom and sinks?'

For other disposal options, the effective dispersal of grey water will depend on what your soil porosity is. You need to disperse the effluent into the ground over as wide an area as is necessary to ensure you don't have any surface water (e.g. through a leachfield).

If the soil porosity is very poor, you'd need to clean the grey water prior to discharging to ground (possibly in a gravel filled tank, such as a horizontal flow or subsurface bed). You'll need some kind of trap at the front end of the system that will catch any solids (hair is particularly likely to block things up and cause problems), and possibly a surge tank, depending on how much the flow rate varies.

Simpler, lower cost options than a leachfield or a reed bed could be a willow bank or a trench arch:

A willow bank is essentially a pile of bark peelings or wood shavings at least 1.5 metres deep and with a surface area of 5 to 10 square metres. It is retained in some sort of frame, which can be a 'living structure' made from willow. Grey water is directed onto the middle of the pile - solid matter is filtered out and humifies, while liquids will drain through and break the wood shavings down into a compost which will itself be a good water-cleaning medium. The water emerging from the bottom will feed the surrounding willows. The willows will need annual pruning, and wood shavings will need to be added less often.

A trench arch is like an elongated soakaway. It is a long gravel-lined trench capped with paving stones that can be pulled up for inspection or maintenance, or a row of pipes cut longitudinally in half.  Raw greywater can rush along it until it finds somewhere nice to settle into. Worms and micro-organisms deal with solid matter and soon create a nice composty medium which treats the water very well. Preliminary research indicates that this might also be effective for raw whole sewage. It was developed by Elemental Solutions.

Please note: if you are not on mains sewerage, the Environment Agency may require that all grey and black water can be treated via your septic tank (or similar system), which would mean you won't get away with putting in a smaller tank or leachfield. Also, while household greywater is generally quite diluted, catering establishments produce very polluted effluents due to all the bits of food waste - so a system would need to be more carefully designed in this case.

Contacts

CAT Consultancy: Eco Sanitation - http://content.cat.org.uk/index.php/water-and-natural-resources-consultancy - email: grace.crabb@cat.org.uk
  CAT experts offer detailed technical advice on composting toilets, reed beds, septic tanks, leachfields, water filters, water conservation, water reuse, rainwater harvesting.
Environment Agency - http://www.environment-agency.gov.uk - 0870 850 6506
  Public body responsible for protecting and improving the environment and to promoting sustainable development.

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