A wastewater with a BOD of 25mg/L is discharged through an outfall to a freshwater stream of mean velocity 0.1m/s. The DO downstream of the outfall is 8.5mg/L. Assume the deoxygenation rate is 0.25/d, the reaeration rate is 0.4 /d and the temperature of 20 degree C (DOs = 9.09mg/L). Compute for the ff: a) Critical distance b) minimum DO c) Oxygen deficit d) Critical time

The 550-bed Atlanta Hospital has a small, activated sludge plant to treat wastewater from the hospital. The average daily hospital discharge is 1.50 m3 per day per bed, and the average soluble BOD5 after primary settling is 450 mg/L. The aeration tank effective liguid dimensions of 10 m x 10 m x 5 m. The plant operating parameters are as follows: MLVSS - 2,600 mg/L; MLSS - 1.20 (MLVSS); Settling sludge volume after 30 min. = 200 mL/L. The F/M ratio is nearly?

A treatment plant treats water at an average daily flowrate of 2.7 m3/s. The water is chlorinated before it flows into a 15000 m3 reservoir. The water flowing into the reservoir has a chlorine concentration of 3 mg/L. Chlorine decays at a rate of 0.24 h-1. Assume the reservoir is well-mixed and the system is at steady-state condition. (a) Determine the chlorine concentration at the discharge point of the reservoir. (b) The treated water flows from the reservoir into a transmission main. The pipe carrying the water has a diameter of 2 m and flows full. In the transmission main, chlorine decays at a rate of 0.19 h-1. Determine the concentration of chlorine 2 km from the treatment plant.

Two circular clarifiers operated in parallel service a single stage bio-tower system (plastic media) that receives municipal wastewater at an average flow (Qaverage) of 2000 m³/d, with BOD5 = 200 mg/L. The internal flow recirculation ratio is 2.4. The maximum overflow rate for the clarifiers is 1.8 m³/m²-hr. The design procedures require that the sizing of the clarifiers be based on "PEAK" flow which is twice the average flow (Qpeak = 2 × Qaverage), and media depth in the biotower is 3.0 m. Determine: (a) The overall BOD5 removal. (b) the surface area and the diameter of each clarifier. (k = 0.06 min¹; n = 0.5),