Water Pollution and Quality - Examples & Applications

Solved Problems

Calculations involving water pollution metrics and DO sag

A wastewater treatment plant discharges effluent into a river. Calculate the initial DO and Ultimate BOD of the mixture just downstream of the discharge point.

Stream Parameters:

Checklist

Flow ( $Q_s$ ) = $8.0 \text{ m}^3/\text{s}$
DO ( $DO_s$ ) = $8.0 \text{ mg/L}$
Ultimate BOD ( $L_s$ ) = $2.0 \text{ mg/L}$

Wastewater Parameters:

Checklist

Flow ( $Q_w$ ) = $2.0 \text{ m}^3/\text{s}$
DO ( $DO_w$ ) = $1.0 \text{ mg/L}$
Ultimate BOD ( $L_w$ ) = $40.0 \text{ mg/L}$

Example

Mixing of Stream and Wastewater

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A water sample has an initial Ultimate BOD (

L_0

) of 20 mg/L. The deoxygenation rate constant

k

is 0.23 day⁻¹ (base e).

Procedure

STEP-BY-STEP

Calculate the BOD remaining after 5 days.
Calculate the 5-day BOD ( $BOD_5$ ) exerted.

Example

Calculate BOD Remaining

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Streeter-Phelps: Critical Time and Deficit

Calculating the point of maximum oxygen depletion

A wastewater discharge mixes with a river. The ultimate BOD of the mix (

L_0

) is

20 \text{ mg/L}

, and the initial dissolved oxygen deficit (

D_0

) is

2 \text{ mg/L}

. The deoxygenation constant (

k_d

) is

0.2 \text{ day}^{-1}

and the reaeration constant (

k_r

) is

0.4 \text{ day}^{-1}

. Calculate the critical time (

t_c

) and the critical dissolved oxygen deficit (

D_c

Example

Calculate Critical Time and Deficit

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Case Study: Eutrophication in Lake Erie

Analyzing the effects of excess nutrient loading

Lake Erie frequently experiences severe algal blooms during summer months. Historically, this has been linked to agricultural runoff containing high levels of phosphorus. Explain the process of eutrophication in this context and its impact on dissolved oxygen (DO).

Example

Eutrophication Process Analysis

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