Monitoring and Detection Using BOD

Biological Oxygen Demand (BOD)

The amount of dissolved oxygen needed by aerobic organisms to break down pollutants present in a water pollution site at a specific temperature in a fixed period of time. The BOD is used to determine the severity of a particular water pollution site. It can also be used to monitor the effectiveness of wastewater treatment plants. BOD directly affects the oxygen level in water bodies. 

Picture of Polluted River Waters

Above Image Taken From: http://www.al-monitor.com/pulse/culture/2012/10/saving-the-jordan.html

 Picture of Pristine River Waters

Above Image Taken From: http://news.nationalgeographic.com/news/2012/12/121214-pictures-unspoiled-rivers-water-grabs/#/water-grabs-unspoiled-waters-niger_61792_600x450.jpg

BOD₅ Test - The BOD value is usually recorded in terms of milligrams of oxygen consumed per litre during a period of 5 days (a basic requirement of this test) incubated at 20°C. Rate of oxygen consumption in the pollution site may be affected by: temperature, pH, the presence of certain kinds of microorganisms, and the type of organic and inorganic material in the water. The greater the BOD, oxygen depletes at a faster rate in the stream. Low dissolved oxygen may cause aquatic organism to be stress, suffocate and die. The presence of pollutants; such as fertilizers and pesticides, human faeces, leftover food, etc. commonly found in urban waste that are being washed into water bodies during storms will increase the level of BOD.

Partial reference from : http://water.epa.gov/type/rsl/monitoring/vms52.cfm

Two Common and Recognised Types:

Dilution Method

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-      Amount of Dissolved Oxygen being measured before and after incubation
-      300ml incubation bottles are being used
-      Buffered dilution water filled with Seed microorganisms
-      Set-up is being stored in the dark for 5 days at 20°C (Prevent Dissolved Oxygen to be produced via Photosynthesis that the microorganisms undergo)
-      Dilution water blank is to ensure quality of dilution water used to dilute, whereby impurities would affect the results
-      Glucose Glutamic acid (GGA) is used to determine the quality of the seed microorganisms
-      A Nitrification Inhibitor is added after dilution water has been added to the sample for cBOD Tests (carbonaceous BOD)
-      Inhibitor prevents oxidation of ammonia nitrogen which supplies nBOD (nitrogenous BOD)
-      cBOD is measured as it is produced by organic matter being broken down
                                                                                                                

 

Above Formula Credited to:   http://en.wikipedia.org/wiki/Biochemical_oxygen_demand

Picture of a BOD Seed  

Above Image Taken From: http://cpcbenvis.nic.in/newsletter/r&d-cpcb/ch70603.htm

Manometric Method

-      Only measures oxygen consumption used up by carbonaceous oxidation
-      Sample will be placed in a sealed container containing a pressure sensor
-      Addition of Carbon dioxide absorber (such as Lithium Hydroxide) above sample level
-      Sample will be stored under similar to conditions as the Dilution Method
-      Oxygen is consumed as Ammonia Oxidation is inhibited
-      Carbon dioxide will be given off
-      The pressure of the total amount of gas will be reduced due to Carbon dioxide being absorbed
-      Electronic Sensors would then detect the fall in pressure and display the amount of oxygen being consumed

Test Limitations

Toxicity

-     -      Some pollutants in urban waste contain chemicals that may affect microbiological growth or activity
-      Some potential sources: Antibiotics in pharmaceutical wastes, sanitizers in food processing or commercial cleaning facilities, chlorination disinfection used following conventional sewage treatment, and odor-control formulations used in sanitary waste holding tanks in passenger vehicles or portable toilets.  etc.
-      Reduction of microbial community to oxidise waste will lower the expected results

Appropriate Microbial Population

-    -      Test relies on microbes that contain enzymes that are used to oxidise the pollutants
-      Some wastewaters (e.g. those from biological secondary waste sewage treatment) will already contain large populations of microorganisms acclimated to the water being tested
-      Part of the waste may be used up during the holding period before the start of the test (Time Lag)
-      Microbes may also take some time to make enzymes

Two Methods of BOD₅ its Test Limitations credited to: http://en.wikipedia.org/wiki/Biochemical_oxygen_demand

BOD Biosensor

-         -        An alternative to measure BOD indirectly

     -        Detects an analyte that combines is a combination of a biological component with a physicochemical detector component
-        Results obtainable quickly (commonly less than 30 minutes)

Limitations:

-      High maintenance costs
-      Limited run lengths due to the need for reactivation
-      Inability to respond to changing quality characteristics (e.g. diffusion processes of the biodegradable organic matter into the membrane and different responses by different microbial species)
-      Uncertainty associated with the calibration function for translating the BOD substitute into the real BOD

BOD Biosensor and limitations credited to: http://en.wikipedia.org/wiki/Biochemical_oxygen_demand

Picture of a BOD Biosensor  

Above Image Taken From: http://www.biyanigirlscollege.com/blog/biosensors