The treatment of water or wastewater to be carried out, their sequence, and results to be accomplished depends upon the quality of raw water to be treated and the extent of purification to be obtained.

In the conventional system, sewage is let into the municipal sewers or open drains. This is being carried to a common collection point where it is treated and disposed off into a nearby water body. This requires laying of a sewerage system, which involves huge amount of earth work excavation. Hence, it is going to be very expensive. Therefore, to reduce the cost of laying, sewer lines are always laid for full flow gradients only. In view of this, the required self cleansing velocities are not obtained. Therefore, due to accumulation of grit, polythene bags, and other deposits the sewer lines start overflowing. This causes lot of inconvenience to the road users. Hence, for maintenance purposes when manhole covers are opened the poisonous gases generated inside the system come out. These gases are very dangerous to the health of living beings.

Further, carrying the sewage to the common collection point, and lifting the sewage for its processing also involve huge capital investments and recurring expenses due to pumping energy. Further, the sewage is likely to contaminate the public water supply lines en-route its transmission.

On the other hand, in decentralized wastewater treatment plants the above problems are reduced to a very great extent. The important objective in this regard is to ensure that the quality of treated water is safe for discharge into a fresh water body or suitable for reuse like toilet flushing, HVAC, and gardening purposes, which reduce the pressure on protected water supply systems.

The concept of Soil Bio-Technology (SBT in short) involves application sewage on a bed of formulated soil media consisting of select culture of soil micro and macro organisms and vegetation to carry out the waste processing. Suspended and dissolved pollutants in wastewater are removed via physico chemical and biological processes naturally occurring in a soil ecosystem. The applied wastewater while percolating through the soil bed in combination with natural oxygenation capacity of the soil media undergoes fundamental reactions. These involve respiration, mineral weathering and photosynthesis to carryout waste processing. The reactions are carried out predominantly in aerobic mode at biogenic pH to prevent unhealthy environment like foul odour. The treated water is of near potable quality free from colour, odour, and enriched with oxygen.

The design of the SBT plant should be carefully worked out to minimize the losses in the pipe network resulting in low energy consumption. As a consequence of this, recycled water is available at a very low maintenance cost adding colours and aesthetic ambience to the plant itself.

Author: Dr. N Surest Kumar