Chapter 5 table of contents biochemical Oxygen Demand (bod) Page
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- Navigate this page:
- Section 1: GENERAL
- Section 2: BOD INTRODUCTION
- Section 4: APPROVED METHODS
- Section 5: SAFETY AND HYGIENE
| Chapter 5
TABLE OF CONTENTS Biochemical Oxygen Demand (BOD) Page Section 1: General 2 Section 2: BOD Introduction 2 Section 3: Glossary 2-3 Section 4: Approved Methods 3 Section 5: Safety and Hygiene 3-4 Section 6: Sampling 4-5 Quiz 5.1 5 Section 7: BOD - Description of Method 5 Section 8: Equipment and Reagents 5-7 Section 9: Determination of Sample Size 7-8 Section 10: Preparation of Dilution Water 8 Quiz 5.2 9 Section 11: Pretreatment of Sample 9-11 Quiz 5.3 11 Section 12: Laboratory Procedure 11-12 Section 13: Calculations 12 Section 14: Interferences 12-13 Section 15: Precision and Accuracy 13 Quiz 5.4 13-14 Section 16: Seed Correction Procedure 14-17 Quiz 5.5 18 Section 17: QA/QC 18 Answers to Quizzes 19-21 Appendix A: References Appendix B: Preparation of Chemicals Appendix C: Sample Bench Sheet Appendix D: Methods Checklist BOD Appendix E: BOD Survivors Guide Appendix F: Bench Sheet
In the presence of free oxygen, aerobic bacteria use the organic matter found in wastewater as “food”. The BOD test is an estimate of the “food” available in the sample. The more “food” present in the waste, the more Dissolved Oxygen (DO) will be required. The BOD test measures the strength of the wastewater by measuring the amount of oxygen used by the bacteria as they stabilize the organic matter under controlled conditions of time and temperature. Section 2: BOD INTRODUCTIONThe BOD test is used to measure waste loads to treatment plants, determine plant efficiency (in terms of BOD removal), and control plant processes. It is also used to determine the effects of discharges on receiving waters. A major disadvantage of the BOD test is the amount of time (5 days) required to obtain the results. When a measurement is made of all oxygen consuming materials in a sample, the result is termed “Total Biochemical Oxygen Demand” (TBOD), or often just simply “Biochemical Oxygen Demand” (BOD). Because the test is performed over a five day period, it is often referred to as a “Five Day BOD”, or a BOD5. In many biological treatment plants, the facility effluent contains large numbers of nitrifying organisms which are developed during the treatment process. These organisms can exert an oxygen demand as they convert nitrogenous compounds (ammonia and organic nitrogen) to more stable forms (nitrites and nitrates). At least part of this oxygen demand is normally measured in a five day BOD. Sometimes it is advantageous to measure just the oxygen demand exerted by organic (carbonaceous) compounds, excluding the oxygen demand exerted by the nitrogenous compounds. To accomplish this, the nitrifying organisms can be inhibited from using oxygen by the addition of a nitrification inhibitor to the samples. The result is termed “Carbonaceous Biochemical Oxygen Demand”, or CBOD. 
Section 3: GLOSSARY Aerobic: A condition in which “free” or dissolved oxygen is present in an aquatic environment. Anaerobic: A condition in which “free” or dissolved oxygen is not present in an aquatic environment. Blank: A preliminary analysis omitting only the sample to provide an unbiased reference point or baseline for comparison. Nitrification: An aerobic process in which bacteria change ammonia and organic nitrogen in wastewater into oxidized nitrogen (usually nitrate). The second-stage BOD is sometimes referred to as the “nitrification stage”. (The first stage is called the “carbonaceous stage”.) Nutrient: Any substance used by living things that promotes growth. Respiration: The process in which an organism uses oxygen for its life processes and gives off carbon dioxide. Seeding: The process of adding live bacteria to a sample. 
Section 4: APPROVED METHODSAlways refer to your facility MPDES Permit and 40 CFR Part 136 for the approved sampling and test procedure. The approved methods for determining the initial and final dissolved oxygen levels in the five day BOD test are the modified Winkler and membrane probe methods. 
Section 5: SAFETY AND HYGIENEWhen testing for BOD, the concerns for safety involve wastewater hazards and exposure to chemicals. Precautions to follow include the following: 1. Cover all abrasions and wear good quality latex gloves when in direct contact with raw wastewater. 2. Wash hands frequently, and always wash hands prior to eating or smoking. 3. Clean up all spills of wastewater or buffers immediately. 4. Wear a protective smock, apron, or lab coat, and surgical or rubber gloves when working in the laboratory to protect clothes and skin. 5. Read all labels carefully and know what to do in case of a spill. 6. Always use a pipette bulb. NEVER pipette anything by mouth. 7. Always pour acids or bases into water, never add water to the acid or base. Mixing concentrated acids or bases with water can create a significant amount of heat. 8. Use care when handling sharps (broken glass etc.). 
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