Few people are aware that along with the law for rainwater harvesting enacted in August 2003, another rule was also introduced. This one made it compulsory for all buildings to treat their greywater through organic or mechanical means and either use it for ground water recharge or for flushing closets.
The rule is an extraordinarily far-sighted one and, if implemented, can make a major contribution to making households substantially self-sufficient in their water needs. About 50-65 per cent of total water usage is for bathing and washing of hands, face and clothes. If this can be reused, that much water can be saved.
However, the rule has remained dormant as no method was specified for cleansing greywater. The mechanical-chemical methods available involve not only high capital expenditure and use of chemicals and electricity but also close follow-up.
There is one simple, eco-friendly and economical method that involves neither mechanics nor chemicals. It imitates a process that is part of most traditional households even today, where kitchen water is diverted into a clump of banana trees. Here, the water is freed of all its organic constituents by the combined effort of the plants and soil bacteria. As the water passes through the soil and reaches the family well, soil bacteria polishes the water fully and renders it fit for all uses.
The method can be adapted by individual houses and apartment complexes even today. Greywater can be diverted to a soil bed of water-loving plants, which must be exposed to at least moderate sunlight so that they grow healthily. You can use Canna indica (Indian shot), Hedychium coronarium (white ginger lily), and any variety of Heliconia, the cyperus plant (umbrella plant), Colocaesia, or banana. There is a widespread impression that today’s soaps and detergents contain a lot of chemicals that are harmful to the body. However, both the organic and inorganic constituents are present only in minute quantities and all the organic ingredients are bio-degradable and will be removed by the plant-soil bacteria combination. Soil bacteria, of course, do not have the ability to remove any inorganic salts but these are so little that they don’t matter.
On a level bed of garden soil, plant the saplings giving at least 2.5 sq. ft. per plant and leaving one foot gap between plants. They can be planted laterally and longitudinally. The level of the soil bed should be uniform so that the greywater spreads over the entire bed and the entire area is available for cleaning the water. Otherwise, water will tend to flow towards the lower areas and the purification will be incomplete.
Water the plants with freshwater for two or three weeks till they take root and stabilise; then divert the greywater into the bed in progressively increased volumes over a week. Thereafter, the process is practically self-sustaining. No smell will emanate from the bed. There may be some inundation of a couple of inches during the peak usage period in the mornings but this will go down in 30 to 45 minutes. No mosquitoes will be generated. The water seeping into the soil augments the shallow water table and can be drawn for reuse through a dug well.
The process can be decentralised in multi-storeyed complexes where the bathrooms on all floors are generally one above the other. If some soil space is available near one such bathroom, only its greywater can be diverted and treated here. A centralised system will involve bringing the greywater from all the bathrooms to be treated in one single soil bed. One can collect the treated water and use it for flushing and gardening. This aspect will be covered in the next article.
An elbow is connected to the outflow pipe and extended to reach the soil bed. No gum or glue piping is used so that for any temporary shutdown, the elbow can be just pulled out to let the water flow into the regular gully and reach the internal sewage line.
If planned during construction, the pipes taking the greywater to the soil bed can be easily concealed underground in the driveways. Since they have to be laid at a slope of 1 in 120, the terminal pipe on the bed will be at a lower level than the abutting ground level. Therefore, the level of the soil bed has to be protected by means of curbing. In one campus, the treatment bed was 4.5 ft below the abutting ground level but it still worked smoothly.
The process is self-sustaining and requires minimal maintenance. If canna plants are used, plants that have borne fruit should preferably be removed but this does not require any skills. For other plants, even this is not necessary. Prevent mounds forming around the plants since these impede the smooth flow of water across the entire bed and the process may have to be begun afresh. If water stagnates, it is either an indication that the plant density is inadequate or the area provided is insufficient. In such cases, the water supply must be disconnected and remedial action taken. The treated water has been tested by Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) and found satisfactory.
This is the second of a three-part series on greywater recycling. For details, mail firstname.lastname@example.org