Question

2. A wastewater treatment plant discharges an effluent containing 3 mg/L of dissolved oxygen to a river that has a dissolved-oxygen concentration of 6 mg/L upstream of the discharge. The saturation dissolved oxygen for the river is 8 mg/L. Assume that the WWTP discharge rate represents 80% of the river flow rate which travels 0.5 km in an hour. The CBOD5 of the river is 5 mg/L with a decay coefficient of 0.25/day. The reaeration coefficient of the river is 0.5/day. What is the location of the critical point: (a) in time; (b) in distance? (c) Why is critical dissolved oxygen a concern and (d) what are the ways to avoid it?

Answer 1

Above problem we can solve as follow first a and b portion are solved in page and other are typed c) critical dissolved oxygen is a concern point because due to disposal of treated waste water has micro organism which are reduce the oxygen level of dissolved oxygen in river. If deficiency of oxygen in river goes below a critical point aquatic life of river are affected and fish, algae and other aquatic plants dead. So for survival of aquatic life in rivers critical dissolve oxygen point is important

D) To avoid the deficiency of dissolved oxygen below the critical point these some precautions should measure

1. Disposal of waste water into river after proper treatment

2. Disposal of waste water at shallow depth of river

3.before disposal of waste water diluted it upto certain degree due to which critical condition can avoid