The overall design of the wastewater treatment plant consists of 4 stages: i)Primary treatment which consists of screening, grit removal and sedimentation ii)Secondary treatment consists of a bioreactor iii)Tertiary treatment consists of nitrogen removal, adsorption and pH control. For plant design, the following parameters are assumed/experimentally determined for the wastewater.
Further, the total flow rate and the concentrations keep varying at different times of the day, as well as are subject to seasonal variations. For example, in morning hours the flow rate and BOD value is high. Similarly, during rainy season solid contents like silt are more due to surface run-off.
Screens typically consist of wedge wire. It is carried out in two phases. In the 1st phase also called coarse screening, the size of the opening is 20-30 mm. It captures the large objects. In the second phase called ne screening the openings vary between 1.5 to 6.4 mm.
Cross section area of the screens is typically 1 m2. For a 1000 kg/h feed of wastewater the impurities removed in this stage are nearly 10 kg/h. When the head loss across the tank exceeds 0.6 m, the screens need to be cleaned. The waste water is pumped into the screening tank using a centrifugal pump, with h = 0:15m on an average.
Authors: Aakash Langeh | Abhijeet Kumar | Ankesh Kumar Singh | Mitul Mundra | Shashank