Aerobic systems : A unique system of sewage treatment in septic tanks

With the fast paced development of urban areas and its spread, the municipalities are unable to provide either sewer lines or proper treatment of the sewage.

This naturally results in two ill effects : (i) Increasing Pollution with untreated sewage and (ii) wasting of water, specially if it can be better treated and reused to an extent.

Apart from the domestic units coming up in such areas, there are professional colleges and industries also in suburban areas. They mostly tend to depend upon ill designed septic tanks which do only half the job, treating the organic waste by up to 50-60%. This results in their (septic tanks) and soak pits getting choked up now and then.

The answer lies in converting their septic tanks to aerobic systems. This can be simply done by putting in inexpensive 'compact aeration unit' cum 'aerobic bacteria generator'. This treats your sewage by 85 to 95%, depending upon the design of the septic tank. The little remaining waste also gets biodegraded over time (with available oxygen and aerobic microorganisms) so that the system is not easily choked and needing frequent cleaning up.

The outflow from the second or third chamber (acting as the settling chamber) is allowed to flow into a treated water tank (or even a soak pit) and from where it is pumped for reuse. This treated water has a B.O.D.  of as low as 30 mg/l (once again depending upon the septic tank design - as given below). This water has negligible odour, specially if pumped through a DMF and used for gardening.

One can get B.O.D. as low as 10 mg/l or lesser with two stage treatment and so that the treated water can be reused for flushing as well.

A properly designed septic tank (if the waste water is treated anaerobically) needs attention to the following (i) the system should have a water retention of at least 2 to 3 days (ii) the water depth should be between 2 to 3 meters (iii) the length breadth ratio is areound 2:1 and (iv) preferably has three chambers. The system of flows from one chamber to the next is also equally important.

With an aerobic system the size of the tank is considerably reduced. The aerobic system costs far less than what you would save on the construction of the septic tank. Power required is between 40 to 200 Watts. For more details visit and and also link to various technical sites mentioned there.



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