Ohio Northern University
CE 3231 - Introduction to Environmental Engineering and Science
Introduction
Chemistry, Microbiology & Material Balance
Water & Air Pollution
Biological Oxygen Demand
When microbes and organic carbon are plentiful in lakes and streams, the
microbes take over. The result is an oxygen depleted system that is very
microbially diverse, but is void of higher trophic level organisms. Understand
BOD and changes in OD is critical to maintaining healthy water quality.
Env Risk Management
Readings for This Class:
5.5-5.6
Lecture 24
BOD Exertion and BOD levels downstream
(Water Quality IV)
Water Quality, Carbon and Nutrient Cycling
Measures of Water Quality
• Dissolved Oxygen (DO) and Oxygen
Demand (OD)
• Total Dissolved Solids (TDS)
• Nutrients
• Metals
• Pathogens
• Organic compounds – Total organic
compounds (TOC)
Oxygen Demand
• Measure of amount of oxygen demanding
organic and inorganic matter in a water
• Measurement
– ThOD –
– COD –
– BOD –
Theoretical Oxygen Demand (ThOD)
• The total amount of oxygen required to:
• Calculated using stoichiometric principles

Calculate ThOD for 1 g/L of glucose
C6 H12O6  6O2  6CO2  6 H 2O
Biochemical Oxygen Demand (BOD)
• BOD = DOinitial – DOfinal
• BOD = Lo – Lt
– L = oxygen consumed
• Lo = initial
• Lt = @ time = t
Biochemical Oxygen Demand (BOD)
• BOD Definition:
• BOD is used:
• Slow analysis:
• Typical analysis:
• Dependent upon:
BOD Jar Test
L
DO Sag Curves
Simple Plug Flow River Model
Objective: derive a mathematical model to predict DO downstream: DO(x,t)
- take your shot at it!
Wastewater discharge
(High BOD, Low DO)
Assumptions:
1. completely and uniformly mixed in the cross flow and
vertical direction
2. neglect pollutant dispersion