Recovery and reuse of gray water
In a generic user, drinking water is extracted from the public water supply system to meet the water needs: this high quality water is used indiscriminately for drinking purposes (eg personal hygiene and cooking) and for non drinking purposes (An example of all the use in WC rinses). There is a double waste: high quality water is used for non-drinking purposes, and it is drained off immediately through the drainage system.
Sustainable watercourse management is based instead on the exploitation of less noble waters and on the use of high quality water only where quality features are really required.
Simple and economically feasible interventions are related to the wastewater component not related to the drainage of the toilets, generally referred to as “gray waters”.
Gray waters are a part of domestic waters that are free of fecal matter and kitchen exhaust waters: they come from natural body hygiene, they come from showers, bathtubs and washbasins.
Gray water is an almost inexhaustible resource and its production does not depend on weather conditions.
Re-use of gray water inside the home could help in reducing the use of drinking water, in this way we will use them twice.
After the first use, the water passes through a micro-clear membrane filter that guarantees the total separation of biomass (solid bodies, bacteria and viruses) from the purified water which, stored in a special container, is then reused for bath WC drainage, garden irrigation, washing machine, car washing and various other washes.
The actions aimed at reducing waste water are basically consisting of:
- the separation of the drainage networks of the black waters (containing the waste of the toilets) and of the gray waters (all other discharge waters);
- the construction of separate water distribution networks (drinking water and non-drinking water);
- the treatment and reuse of purified gray water for non-drinking purposes, such as irrigation of green areas, filling of toilet flushing vessels, and washing of external areas.
Gray waters can be purified much faster than black waters: probably the most significant difference is the rate of degradation of pollutants in the gray waters. Black waters contain organic substances that have undergone one of the most efficient degradation processes in nature, that of the human gastrointestinal tract; It is thus easy to understand that the residues of this process can not be decomposed rapidly once inserted into water, that is an environment not compatible with the bacterial population contained therein.
For example, in five days of organic degradation of organic matter, only 40% of the present organic matter undergoes complete mineralization, while in the case of gray waters a 90% removal is achieved at the same time. This rapid decay of the organic matter present in the gray waters can be explained by the abundance of sugars, proteins and fats, easily available to the bacterial flora, characteristic of this type of reflux.
Gray waters also contain only 1/10 of total nitrogen and less than half the organic load over the black waters, as can be seen from the following figure, which reports the data of analytical campaigns conducted in two distinct scenarios in two different countries.
A sustainable design for the treatment of gray waters for reuse must take into account the following factors:
- adaptability to changes in hydraulic and inlet loading;
- efficiency in degradation of organic matter;
- high abatement of bacterial charge;
- simplicity and economy of management and maintenance.
It is also possible to combine greywater treatment with rainwaterrecovery: in this case, the purged water storage tank will be one.
Greywater treatment and reuse systems can be:
|UNDERGROUND TANKS||TANKS INSIDE THE BUILDING||COMBINED RECOVERY OF RAIN AND GRAY WATERS|
Recovery of rainwater
Rainwater is a continuously available source and requires simple and cost-effective treatments for their reuse, for non-drinking purposes.
Plants for rainwater recovery allow for the reuse of water from rain-fed systems of households, providing an ideal reservoir for irrigation of green areas, for washing vehicles, draining water services, and so on. It is estimated that in households about 50% of the daily water requirement (which corresponds to a daily demand of 150 to 200 liters per day) can be provided by the recovery of rainwater.
For the dimensioning and design of these plants, reference is made to the complete regulation on this topic “DIN 1989 – Plants for the use of rainwater”.
The strengths of the system are:
- the gratuity of the conferment;
- the absence of calcareous deposits in the pipes and electrical resistors of washing machines (washing machine, dishwasher) and consequent saving on electricity consumption;
- saving detergents (up to 50%) for the lowest water hardness
|SCHEMA FUNCTION SCHEMA AND COMPONENTS OF AN AUTOMATIC WATER RECOVERY SYSTEM|