DISPOSAL OF EFFLUENT FROM THE SEPTIC TANKS AND RECOMMENDATIONS FOR THE DISPOSAL

As per the provision made in the residential installations, it is considered that as long as the dilution per head is more than 25 litres and less than 180 litres, a septic tank having a content of about 0.071 cu. m per user will do the work required. It has, however, been reported that septic tanks with as low a dilution as 9 litres per head per day built in water scarcity areas have also worked satisfactorily. According to the experiment carried out in India , if the sewage is stronger than 25 litres per user, there is not enough water for the necessary reaction to take place in the tank, while if it is weaker than 180 litres per user it goes through the tank too fast and remains under treated . Said limits of the capacity of the tank between 0.476 to 0.0672 cu. m.per user. Effluents from both the over and under-treated tanks clog the filters. However, it is the general opinion that, for the proper operation of a house drainage system, a minimum water supply of 90 litres per capita per day should be available. As it is not possible to estimate the exact number of users or the amount of dilution water for any proposed installation, it will be safe to provide a capacity of about 0.084 to 0.112 cu. m per user for small tanks and 0.07 cu. m for large tanks for Indian conditions where the baths and sinks are also connected with the system. The minimum capacity of a septic tank should not be less than 1.14 cu. m which is sufficient for 10 to 15 users. Surface and sub -soil water should be excluded from finding way into the septic tank. Waste water may be passed into the septic tank provided the tank and the means for effluent disposal are designed to cope up with this extra liquid. Depending on the location of the water table and the nature of the strata, the type of disposal for the effluent from the septic tank is decided accordingly. As the disposal works are generally becoming a main problem in a sewage scheme and require very careful consideration. Place of disposal of sewage is of primary importance and very often it governs the entire scheme. As such a soak pit should not be less than 30 mt away from a well or any source of water supply.