Greywater Treatment.
Advanced Geywater system
Roughing Filter
Aerobic Pre-treatment - suitable for showers, hand-washing and laundry* (see note below) water treatment.
The aim of this stretch filter treatment technque is simply the removal of large particles and fibers to protect the subsequent infiltration pipes from clogging and transferring it as soon as possible for treatment into a biologically active, aerobic soil-zone environment where both macro- and microorganisms can thrive.
Stretch-filters are made to retain fibers and large particles and allow the rest of the organic material to travel on to the next stage of processing. This filter is suitable for public facilities where the principal source of greywater is hand-washing and showers without any food waste to speak of.
If this type of filter is used to remove food wastes, these will accumulate in the filter which then becomes anaerobic and makes the effluent malodorous.
The result is often that too frequent changes of the stretch-filter becomes necessary ---thus creating an undesirable,high-maintenance situation. See diagram below for a typical Clivus greywater management fabric filter configuration:
*Beware of the use of harsh detergents and bleach if the water is to used in or near gardens growing edible plants. Some surfactants are associated with controversial hormone-mimicking characteristics that we need to be aware of. We also need to be aware of handwashing soap containing antibacterial chemicals which are totally unnecessary and do not improve cleansing.
Anaerobic to aerobic pre-treatment
Grease-trap/septic tank + sandfilter + sample/pump pit
If any significant quantity of food waste enters the system from dishwashers and kitchen sinks receiving cooking grease and a fair amount of food residue, this option is recommended.
A typical installation is not very different from a traditional system; but the treated effluent is of much better quality and does not pollute nearly as much. Ideally, it should consist of a three-stage septic tank for sludge and grease separation.
The separated sludge can thus be removed less frequently [every fourth year instead of bi-yearly as is standard practice with many conventional systems]. The outgoing effluent in the septic system is anaerobic. Following the septic tank is a sandfilter designed for restoration of aerobic conditions.
The final treatment stage leading to purified water of near potable-quality is treatment in a planter bed. This is not the most inexpensive solution. It is, however, one of the most effective,simple-to-maintain on-site treatment techniques available today.
Planter Soilbox Design
Soilboxes have been used for greywater purification since 1975 with excellent results.
The planter bed has to be well drained to prevent the formation of a water-logged zone in any part of it. Therefore, its bottom contains a layer of polyethylene "actifill" or pea gravel to provide effective drainage.
A layer of plastic mosquito-netting on top of the actifill prevents the next layer of coarse sand from falling through. On top of the coarse sand is a layer of ordinary concrete-mix sand, while the top two feet consist of humus-rich top soil. Clay soils must not be used.
Information reproduced with permission of Carl Lindstrom.
There are many other methods of Greywater treatment which can be found at Carl Lindstrom's website on Greywater
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