3 Common Tests to Determine Organic Pollution in Wastewater

3 Common Tests to Determine Organic Pollution in Wastewater

Wastewater treatment facilities are reliant on biological processes to break down a wide variety of organics to keep them functional. They use these processes to convert wastewater and sewage into effluent and safely return the product to the water cycle with minimal impact on the environment.  To ensure the safe and efficient success of these processes, chemical measurements of specific parameters are necessary to monitor and report on. The specific tests and values can vary by location but three very common measurements performed in the industry are BOD, COD, and TOC.

These measurements can provide valuable insight into the microbe’s ability to thrive during the treatment process. Optimization of these microbes will have a direct impact on the facilities’ treatment performance. Too much organic matter and the microbes can grow too quickly causing process issues in the plant such as clogging. Too little organic matter and the microbes can die off causing ineffective treatment for the effluent. Careful monitoring ensures a proper microbial environment allowing for a safe return of the water back into the water cycle. This blog will cover these common tests providing instrumental background and usage in the wastewater industry.  

 3 Common Tests to Determine Organic Pollution in Wastewater

Test Overview: 

What is TOC?

Total Organic Carbon (TOC) is often used as a non-specific indicator of water quality. In the natural process of our environment and the man-made processes of industry, the ubiquitous nature of Carbon provides a screening tool to determine the status of water quality. In general, TOC works by converting all organic molecules in a given sample into CO2 via some type of oxidative process. This CO2 is then measured via the instrument’s detector. The detector’s response is proportional to the concentration of the Carbon in the sample which can then be correlated to the quality of the water.

TOCs typically come in 3 varieties: High-Temperature Catalytic Oxidation, Heated Persulfate with NDIR Detection, and UV Persulfate with either NDIR Detection or Conductivity/Membrane Conductivity Detection. TOC instruments have been used in the wastewater industry to determine contamination from naturally occurring compounds, man-made compounds, viruses, bacteria or to provide insight into biological growth.

Looking for a TOC Analyzer? You can view OI Analytical's TOC Portfolio Here. 

What is BOD?

Biochemical oxygen demand, or BOD, is a procedure for determining the amount of dissolved oxygen being used by microorganisms in a given sample. Oxygen is needed by aerobic biological organisms in a body of water to break down organic material. This Biological Oxygen Demand is affected by the same factors that affect dissolved oxygen, things like temperature and pH. Measuring Biochemical Oxygen Demand requires taking two measurements. A measurement at time zero (initial) where the amount of Dissolved Oxygen (DO) is taken. The sample is then allowed to incubate in the lab for 3-5 days and the sample at which point the sample is tested again for the amount of Dissolved Oxygen (final). This resulting difference in the initial and final number represents the amount of Oxygen consumed by microorganisms to break down the organic matter present in the sample during the incubation period.

Check out our BOD Testing Brochure to learn more! 

What is COD?

Chemical Oxygen Demand or COD is another test that is used to measure the quality of water in wastewater treatment facilities. In COD testing a known amount of strong oxidizing agent under acidic conditions is used to convert all the organic species into CO2. Once this oxidation is complete the amount of the remaining oxidizing agent left in the solution is measured. This is typically done by titration and an indicator solution. The stoichiometric relationship between oxidizing agent and Oxygen is used to calculate the amount of oxygen that was consumed during the reaction providing the analyst a COD number typically expressed in mg/L. The test takes approximately 2-3 hours to complete and unlike BOD, the test is not affected by heavy metals or other toxic compounds in the sample so the test is often used for samples where BOD cannot be used.

3 Common Tests to Determine Organic Pollution in Wastewater

 

Technique comparison:

TOC advantages

    • Time: Relatively fast compared to COD and BOD results in less than 2hrs
    • Quantitative
    • Automation limits user errors
    • Low cost of ownership after the initial cost of the instrument
    • Minimal sample handling
    • Not subject to most sample interferences
    • The lower detection limit of 0.1 mg/L
    • Precise and accurate results

TOC Disadvantages

    • Non-specific
    • Doesn’t quantitate the overall reactivity of the organics in the sample
    • Many regulations are still written for BOD and COD vs TOC

 3 Common Tests to Determine Organic Pollution in Wastewater

BOD Advantages

    • Historically used with many regulations calling for its use
    • No hazardous waste generated
    • Used by regulators for permits

BOD Disadvantages

    • Time: long measurement typically 3-5days
    • Very susceptible  to interference
    • Is dependent on Matrix
    • Poor data reproducibility between tests
    • The poor detection limit of 2 mg/L
    • A large amount of sample handling required

COD Advantages

    • Time: Several hours compared to days for BOD
    • Less affected by toxic components in the sample so can be used to measure samples where BOD is not possible.

COD Disadvantages

    • Nonspecific: doesn’t distinguish between Inorganic and Organic Carbon 
    • Susceptible to interference by some halides and nitrates
    • Need to handle toxic chemicals to perform the test

 

Ensuring our wastewater effluent is safe and poses little threat to our environment is essential for the protection of our ecosystem. Tests like these help wastewater treatment plants operate efficiently and safely. The chosen test or tests are often dictated by state and local regulators. Xylem has a long history of providing technical expertise in the wastewater industry and continues to innovate to provide better, easier to use solutions for our customer.

If you would like to talk more about our wastewater solutions, contact us today!


Monitoring organic contaminants in water and wastewater streams? Want to learn more about substituting TOC for BOD? Hear from our industry experts!

BOD measurements have for years been used to quantitate the amount of dissolved oxygen in a given sample that is available for aerobic biological organisms. The typical measurement monitors the changes in these levels over a period of time, typically 5 days, to help the analyst understand the quantity of bacteria in a given sample.

This lengthy measurement time can make it challenging to implement process control in wastewater treatment facilities.  Total Organic Carbon (TOC) is a technique that quantitates Total Carbon (TC) content quickly but is less specific than BOD measurements but has been shown to provide a good correlation for BOD. In this presentation, Dr. Ojo will cover the potential for TOC to be used for BOD measurements in the wastewater industry. 

When: 

We will be live on January 19, 2021, at 11 AM EST. You should attend this webinar if you're interested in learning more about substituting TOC for BOD measurements in wastewater. 

3 Common Tests to Determine Organic Pollution in Wastewater