In this kind of wastewater filtration, the sewage performed on the contact subject material is permitted to stand undisturbed for some time previous than, being emptied and an length is permitted previous than recharging the contact beds. All the way through the ‘contact duration’, when the filter is standing entire, the high quality suspended particles of sewage are deposited on the contact subject material and worked over by way of the anaerobic organisms. All the way through the ’empty duration’ that follows next, the deposited topic is oxidized by way of the aerobic bacteria. It is then washed off the contact subject material and carried out with the sludge effluent on the next emptying of the tank.
Contact beds are watertight tanks with masonry walls and truly so much an identical in development to an intermittent sand filter. The contact subject material is fabricated from broken stone referred to as ballast and is of 2.5 – 7.5 cm gauge. The tank is full of the sewage over a duration of an hour; allowed to stand entire over a duration of two hours, then emptied by way of underdrains. This process takes another hour. The tank is now left empty for 3 to 4 hours previous than admitting the next charge. (Thus with an entire working duration in a shift of 8 hours, the contact bed may also be worked in three shifts daily). The herbal loading in this case is in a position the identical i.e., 1.1 million liters in line with hectare in line with day.
The contact beds means is now most simple of ancient hobby and not often used. This is principally as a result of the loss of efficiency ended in by way of the exclusion of air when the tank is standing entire. For an efficient natural movement, it is an important that the aeration must be all over the mass of sewage. It has therefore, been superseded by way of further setting pleasant natural wastewater treatment process, as in relation to trickling filter wastewater treatment means and activated sludge plants. Alternatively, the contact beds have some merit when compared to the trickling filters as:
(i) Lesser operating head required
(ii) Freedom from filter (psychoda) flies
(iii) Lesser nuisance on account of smell