
Concept explainers
Two communities, A and B, are found on two opposite sides of flowing river with a 9.10 m3 /s rate of volumetric flow, an uniform average speed of 0.25 m/s, an average depth of 4.0 m, an average temperature of 13°C, a chloride concentration of 8.0 mg/L, a 5.0 mg/L concentration of ultimate BOD, and an 8.0 mg/L concentration of dissolved oxygen. Both communities continuously discharge wastewater at the same point in the river where instantaneous mixing is assumed. The discharge of community A, which has an ultimate BOD of 48.2 mg/L and a dissolved oxygen concentration of 2.50 mg/L, is 2.10 m3 /s. On the other hand, community B discharges 1.80 m3 /s of wastewater, which has an ultimate BOD of 62.9 mg/L and a dissolved oxygen concentration of 1.50 mg/L. Just downstream of the downfall of both point sources, the deoxygenation rate constant is observed to be 0.22 day-1 .
(a) What are the ultimate BOD and the initial oxygen deficit of the river and wastewater mixture just downstream of the downfall?
(b) Locate the point downstream within which the minimum amount of dissolved oxygen is reached and the time it will take to reach this point along the river length downstream.
(c) What is the minimum value of the dissolved oxygen at this point?
(d) What is the BOD and the dissolved oxygen concentration of a water sample at 36 km downstream of the point of wastewater discharge?

Step by stepSolved in 2 steps

- The herbicide atrazine is accidentally spilled into a river, resulting in 80 μg/L atrazine concentration in the water column at the site of the spill. The intake of a local drinking water supply is located 15 km downstream of the site of the accident. The average river flow velocity is 0.5 m/s and the dispersion coefficient is 50 m2/s. Assuming steady-state conditions in the river and that advection is the dominant transport mechanism, approximately how long will it take for the chemical to reach the drinking water intake? Assume that no transformation of atrazine will occurarrow_forwardAm acquifer is recharged by precipitation that infiltrates through fertilised fields. The concentration of nitrate in the groundwater is 1.25mg/l. Th4 nitrate is carried by flowing groundwater into a large fish pond the farmer has on her property. The average linear velocity of the groundwater is 0.087m/day and the aquifer porosity is 0.25. The aquifer has an approximate saturated thickness of 2.55m (depth of saturated soil above bedrock). The flow path into the pond is 87wide. What is the mass loading of nitrate into the pond in units of g/day?arrow_forwardFlow rate: 1.5 m3/s Pollution: pesticide permethrin Lake size: 100m x100m x 2.5m Steady state concentration of permethrin leaving the lake is 1.4 ppm Average cross-sectional area of the river is 2.7 m2. Half-life of permethrin in this environment is 19 hrs. What is the concentration of permethrin entering the lake and what distance downstream of the outlet would the concentration be less than 1 ppm?arrow_forward
- A city wishes to discharge wastewater primary effluent to a river which supports a trout. The state requires the city to show that the trout population is protected. Trout require a minimum of 4 mg/l of dissolved oxygen to survive. Determine the minimum downstream dissolved oxygen concentration from the following information about the wastewater discharge and river. Does the minimum dissolved oxygen concentration meet the requirements? Wastewater discharge=0.45m3/s, river flow rate= 8.5 m3/s, river cross-sectional area=19m2, dissolved Oxygen concentration in the wastewater= 0.2mg/l, dissolved oxygen content of the river upstream = 8.1mg/l, saturation dissolved oxygen concentration at 20 C= 9.0 mg/l, BOD concentration in wastewater = 85 mg/l, BOD concentration upstream in the river= 0.2 mg/l, BOD decay constant = 0.2 d-1, and the reaeration constant for the river= 0.4 d-1.arrow_forwardThe town of Viracocha discharges 17,360 m³/day of treated wastewater into the Pachacamac Creek. The treated wastewater has a BOD5 of 12 mg/L and a BOD decay constant, k, of 0.12/day at 10 °C. Pachacamac Creek has a flow rate of 0.43 m³/s and an ultimate BOD, Lo, of 5 mg/L. The DO of the river is 6.5 mg/L and the DO of the wastewater is 1.0 mg/L. Compute the DO and the initial ultimate BOD, Lo, after mixing. Draw the Mass Balance Diagram.arrow_forwardAn action will release DO and BOD to a large low velocity river at a location where the existing conditions of the river have already been determined. Assess the impacted conditions (as a result of this action) at a location 10,000 m down-river from where the action releases the pollution. River: Q = 2 m³/s, A=1m², T = 15 degC, L = 5 mg/L, DO = DOsat Source1: Q = 0.5 m³/s, T = 25 degC, L = 100 mg/L, DO = 1 mg/Larrow_forward
- Structural Analysis (10th Edition)Civil EngineeringISBN:9780134610672Author:Russell C. HibbelerPublisher:PEARSONPrinciples of Foundation Engineering (MindTap Cou...Civil EngineeringISBN:9781337705028Author:Braja M. Das, Nagaratnam SivakuganPublisher:Cengage Learning
- Fundamentals of Structural AnalysisCivil EngineeringISBN:9780073398006Author:Kenneth M. Leet Emeritus, Chia-Ming Uang, Joel LanningPublisher:McGraw-Hill EducationTraffic and Highway EngineeringCivil EngineeringISBN:9781305156241Author:Garber, Nicholas J.Publisher:Cengage Learning





