Chemical Oxygen Demand, or COD, is a vital measurement utilised in the wastewater industry to understand the amount of dissolved oxygen within water.In this guide we cover everything you need to know about COD and reagents.
What is Chemical Oxygen Demand?
Chemical Oxygen Demand (COD) measures the amount of oxygen necessary to oxidise organic matter within a specific quantity of water. COD testing provides information about water's capacity to consume oxygen while decomposing organic matter, such as greases, proteins and carbohydrates produced from various industrial processes. A higher COD measurement indicates a higher level of pollutants.
The result of COD testing provides insight into how much of an impact the release of wastewater will have on the water it is discharged into, ensuring dissolved oxygen isn’t depleted to a level that can be harmful to plants and wildlife. If COD is too high, wastewater is then treated appropriately to reduce this impact.
Why is COD measured?
Chemical Oxygen Demand provides an accurate picture of the pollutants within water. Companies that produce or treat wastewater measure COD as part of water utility compliance to prevent problematic pollutants from entering larger bodies of water.
Guidance provided by the UK’s environment agency in 2019 defined COD monitoring as a requirement for water utilities, providing specific compliance limits for sensitive areas, industrial waste, and other discharges. Wastewater from industrial processes is tested using COD, and other related methods to determine the level of pollutants after each stage of treatment and before discharge to reduce their impact on the environment.
COD vs BOD
BOD is also known as Biochemical Oxygen Demand. BOD testing also provides measurement to estimate the pollution within a water sample, but the process is different. While COD focuses on oxygen required for chemical breakdown, BOD looks at the biological breakdown of the same organic pollutants with microorganisms.
COD and BOD both help in understanding and measuring pollutants in wastewater. COD is more efficient with same-day results and allows businesses to comply with ISO requirements with the right instrumentation and reagents, whereas BOD can take five days when using specialised instrumentation.
Where is COD testing used?
COD testing is primarily used in wastewater treatment and discharge, allowing companies and water utilities to monitor the levels of pollutants in water. By measuring COD, the appropriate treatments can be used to reduce ‘organic loading’ before wastewater can be discharged into a large body of water. COD monitoring is used throughout the storage and treatment process to ensure full compliance with UK regulations.
Some examples of industries that require water discharge in the UK include:
- Fish processing
- Milk processing
- Potato processing
- Soft drink bottling and manufacture
- Fruit and vegetable product manufacture
- Meat processing
- Breweries
- Alcohol production
- Plant-based animal feed manufacture
- Glue and gelatine organic manufacture
- Malt houses
Some of the main ways COD testing is used include:
Gaining insight into the pollutants in wastewater
A wide range of industrial and manufacturing processes produce wastewater. COD testing at this stage on a sample of wastewater, whether by the companies that produce it or by water utilities, provides insight into the average pollutants produced by that specific process. This information can then be utilised to plan out treatment for collected wastewater to meet necessary standards.
Testing wastewater after primary treatment
Primary treatment of wastewater involves the use of sedimentation basins or clarifiers. These tanks effectively stop the water flow, giving solids suspended in the water time to settle while oils, greases and fats rise to the surface for skimming. This process removes a significant amount of pollutants from the water, after which COD testing can help determine the oxygen demand level from remaining pollutants.
Testing wastewater after secondary treatment
Secondary wastewater treatment typically involves an aeration basin, where bacteria and microorganisms are introduced to convert organic matter to water and carbon dioxide. This process lowers organic pollutants, helping to reduce oxygen demand, which is tested again before discharge.
Adhering to discharge limits
Discharge limits in the UK vary based on the water or sewerage a business or utility is discharging into, based on the types of pollutants within the wastewater. Sensitive areas defined by the Environment Agency, such as eutrophic freshwater bodies – areas supporting dense plant growth with high levels of nutrients – may have stricter limitations to other bodies of water.
What tools do you need for COD measurement?
A spectrophotometer
Spectrophotometers are an accurate solution for COD testing alongside a wide range of other specialist parameters required for wastewater discharge and monitoring. Hanna’s Iris Spectrophotometer is an innovative and compact option for testing, with over 100 methods and an easy-to-use favourite methods system.
A thermoreactor
A heater block or thermoreactor is used to heat up COD wastewater samples with reagent to comply with ISO requirements. The HI-839800 Heater Block features timers and covers three different temperature ranges required by various tests, with a capacity for up to 25 simultaneous digestions
COD reagents
COD reagent vials are combined with water samples, heated and then placed in a spectrophotometer to provide an accurate measurement. Hanna reagents include options for ISO compliance, with a range starting from 0.
What should you consider when buying reagents?
Here are a few things to consider when choosing reagents:
Availability of reagents
Reagents are single-use products, with 25 vials included in a standard box within the Hanna range. Choosing a reagent supplier that can deliver stock promptly in line with your testing requirements is key to meeting compliance and maintaining a testing schedule.
Volume of testing
Laboratories and services that run outsourced tests from other businesses will have higher demand than companies testing their own wastewater. A supplier that can provide fast delivery on higher volumes of stock is key to providing customers with the prompt service they require.
How to improve cost and time efficiency with COD reagents
Here are a few of the ways you can achieve better efficiency and reduce costs with COD testing:
- Choosing a UK-based supplier: Hanna Instruments stocks all of our reagents at our UK facility, reducing the risk of stock delays and providing next-day delivery on reagents as required to ensure you have the consumables needed..
- Switching to a different brand: Hanna’s reagents are compatible with instrumentation from other brands such as Lovibond, Palintest or Hach, allowing businesses to comply with ISO requirements with readily-available reagents.
- Buying in bulk: Opting for a supplier that can provide reagents in the required volume is an effective way to improve efficiency by having the right number of tests to hand as and when required.
Switch and save on COD reagents at Hanna Instruments UK
Hanna Instruments are the ideal choice for reliable, UK-stocked COD reagents. Browse our range online now.
For advice and guidance on COD process and testing, get in contact with our experts directly on 01525 850 855 or via email.
