The biochemical oxygen demand (BOD) is the amount of oxygen that can be consumed by biological microorganisms when they decompose organic matter in water. The chemical oxygen demand (COD) is the amount of oxygen consumed wen organics are chemically oxidised (usually using dichromate) under acidic conditions. Organic matter can contain bonds to elements such as nitrogen, which breaks down into ammonia as it is degraded. The ammonia creates an oxygen demand as it undergoes nitrification and converts to nitrate, with its demand included in BOD testing. Dichromate, however, does not oxidise ammonia into nitrate, so nitrification is not included in the standard COD test.
COD and BOD measure the potential deoxygenation of the water that can occur as the organic matter is broken down, and high BOD/COD concentrations can cause species such as fish to die, and create a shift towards a bacteria and worm dominated aquatic ecosystem. Many industries can create water high in COD/BOD, such as municipal (sewage) treatment , agriculture and mining.
BOD is the traditional and most widely used measure to establish the concentration of organic matter in wastewater, however BOD testing usually takes 5 days for microorganisms to interact with organic matter and in some cases heavy metals or toxic compounds inhibit testing. COD testing takes a matter of hours and can be used to determine an estimate of the BOD concentration to allow quick adjustments to treatment processes.
BOD is commonly treated by biological methods, such as adding bacteria and providing favourable conditions to break down the organic matter quickly. Sewage treatment plants commonly use return activated sludge (RAS) as a bacteria source, which is added to aerated water and aerated to treat organics in the water. Once the bacteria have fed on the organics and been removed from the water, some of them are returned to the start of the process to continue the process.
Our CIF® (continuous ionic filtration) technology combines continuous physical filtration and ion exchange using carefully selected resins to remove organics from water, reducing BOD.
Our BIOCLENS™ encapsulated bacteria technology contains a suspended matrix of living bacteria contained inside a PVA lens. Ammonia ions and nitrates diffuse into the lens with the water, and the bacteria perform either nitrification or denitrification processes to remove the ammonia ions or nitrates, reducing the BOD. The lens’s shape allows for higher diffusion ratios than other shapes and allows reuse and a clear separation of the bacteria from the liquid being treated.
Our BIONEX™ technology is a combination of using ion exchange resins to remove substances that contribute to BOD from the water, and then using our encapsulated bacteria lenses to treat the waste generated. This robust process allows for small site footprints, zero brine production, consistently low total nitrogen (TN) concentrations, and low energy and chemical consumption.
To find out more about our COD/BOD treatment capabilities or to discuss a project, please