Organic matter is an inevitable part of wastewater, regardless of how that wastewater is generated, whether from industrial applications or from residences. Much of the organic matter in the wastewater is treated using biological processes. The organic matter is turned into sludge and disposed of safely, or utilized as a part of manure for plants.
The biological matter in wastewater must be effectively measured and treated. Otherwise, it could cause serious environmental problems and severely limit the efficiency and performance of the wastewater treatment plant.
Why is it important to monitor biological waste in water?
Measuring the biological waste in wastewater allows the plant to create an optimum environment for microbes to grow. If there is a high concentration of biological matter in the plant, the microbes too will thrive without control. This could lead to process issues such as clogging in the plant.
A digester tank overloaded by organic matter leads to serious issues resulting in downtime. Death of the bacteria from pH changes, reactor shutdown, cleanup, and recommissioning procedures can drive up the cost and time of ensuring a smooth treatment of biological waste.
In many cases, wastewater originating from applications such as the processing of sugar, for instance, contains soluble nutritional organic material. The microbes could thrive out of control on this matter, depleting the dissolved oxygen in water bodies when such water flows into these bodies.
On the other hand, if the biological matter is too low, it could hamper the growth of microbes, and limit the effectiveness of the treatment process.
Effective treatment of the biological matter in wastewater
Effective treatment of the biological matter, as well as organic carbon, helps businesses comply with environmental regulations. Additionally, treating organic carbon in the water helps limit the presence of corrosive compounds that could damage costly equipment.
Three key tests are used to measure and treat biological matter in wastewater.
Biological Oxygen Demand (BOD)
BOD is denoted the amount of oxygen required for the bacteria in a natural water body to decompose organic matter at a specific temperature. If the BOD is higher, it means more of the dissolved oxygen in the rivers or lakes will go towards decomposing biological waste. This will endanger aquatic life.
BOD test procedure
A count of dissolved oxygen is taken and logged as time zero (initial count). The water sample is then allowed to rest in the lab for 5-6 days. After this, the sample is tested again to obtain the final count of dissolved oxygen level.
The difference between the initial and final BOOD counts is the amount of oxygen consumed by the microbes to break down the organic matter in process water.
The BOD test only yields an estimate of the oxygen that the microbes will need to decompose the organic waste. This test is plagued by issues such as long testing time and inaccurate results.
Chemical Oxygen Demand (COD)
COD is the amount of oxygen required to oxidize organic matter using a chemical oxidant. The COD test involves using chemical oxidants that oxidize both organic as well as inorganic matter in wastewater.
COD testing procedure
In the COD test, strong oxidizing agents are used to convert all the organic spices in process water into carbon dioxide. Once the oxidation is complete, the amount of oxidizing agent remaining in the water is measured using indicator solutions and titration. The amount of oxygen that was consumed during the reaction is then calculated using the stoichiometric relationship between oxidizing agent and oxygen.
While the BOD test takes 5-6 days, COD test takes a few hours to complete, and yields a more accurate results. What’s more, the BOD and COD measure are correlated. The COD calculations can be used to determine a specific BOD range and improve wastewater quality.
Explore the correlation between BOD and COD on our blog here.
Total Organic Carbon (TOC)
Carbon is an element present in natural as well as processed water from the industry. This universal presence of carbon can be used as a tool to gauge water quality. This is done with the TOC test.
TOC test procedure
test converts all organic matter in the process of water into carbon dioxide. The total amount of carbon in water is then measured to correlate to the quality of water.
There are 3 types of TOC tests
- Heated Persulfate with NDIR Detection
- High-Temperature Catalytic Oxidation
- UV Persulfate
TOC instruments are used to monitor water contamination from naturally occurring compounds, man-made compounds, viruses, bacteria or to provide insight into biological growth.
Conclusion
In the case of BOD and COD tests, the oxygen content needed to decompose organic matter is the base of the measurement. These tests yield diverse levels of oxidation of various compounds within the process water. However, the carbon concentration in water remains constant. Hence TOC test, which can be done in a few minutes, is the more accurate and preferred method to measure organic content in process water.