Grey Water Recycling

Greywater is wastewater generated from domestic activities such as laundry, dishwashing, and bathing, which can be recycled on-site for uses such as landscape irrigation and constructed wetlands. This wastewater contains no fecal matter (human feces). Greywater differs from water from the toilets which is designated sewage or blackwater to indicate it contains human waste. Greywater makes up 70-90% of the residential water.

Definition

Greywater gets its name from its cloudy appearance and from its status as being between fresh, potable water (known as "white water") and sewage water ("black water"). In a household context, greywater is the leftover water from baths, showers, hand basins and washing machines only. Some definitions of greywater include water from the kitchen sink. Any water containing human waste is considered black water.

Elimination of greywater

Domestic wastewater is usually combined at the sewer, so that grey- and blackwaters are removed together using a shared sewerage system in a process called elimination.

Sewage water can then be treated to limit pollution and health risks, before being returned to the environment at large. Most greywater ends up as effluent in rivers and oceans in this way.

There are other alternatives to eliminating greywater that allow for efficient use; using it to irrigate plants is a common practice. The plants use contaminants of greywater, such as food particles, as nutrients in their growth. However, salt and soap residues can be toxic to microbial and plant life alike, but can be absorbed and degraded through constructed wetlands and aquatic plants such as sedges, rushes, and grasses.

Implimentation Of Green Water Treatment

Advanced Geywater System

Roughing Filter

Aerobic Pre-treatment - suitable for showers, hand-washing and laundry 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

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.