Rimozione BOD e COD nel Trattamento Acque

Removal of BOD and COD from Wastewater

Industrial and civil wastewater may contain high concentrations of organic matter, which can be measured “indirectly” through the parameters BOD and COD. Treatments with aerobic and anaerobic bacteria are useful for decreasing these two values. Dissolved air floaters and biodisc oxidation systems are two MITA technologies for removing BOD and COD.

BOD and COD removal: the need in water treatment

Civil and industrial wastewater may contain a number of organic pollutants, which can be measured by the parameters BOD (Biochemical Oxygen Demand) and COD (Chemical Oxygen Demand).

Both BOD and COD are two “indirect” measures of the amount of organic matter, thus composed of carbon, that must be degraded to purify water. In fact, since direct measurement of carbon is difficult, the two values are calculated as follows (both are expressed in mg/l).

  • The BOD value is the amount of oxygen, dissolved in water, that is consumed by aerobic bacteria that degrade a certain amount of organic material in a water sample. All this is done under well-determined temperature and time conditions: 5 days of incubation at 20 °C. In fact, it is more properly referred to as BOD5.
  • In contrast, the COD value indicates the amount of oxygen required to chemically oxidize the totality of organic matter in the reference water sample. Indeed, it should be specified that aerobic bacteria cannot degrade all organic matter: instead, COD considers all that can be oxidized (and is therefore always higher, as a value, than BOD).

Wastewater, particularly industrial wastewater, can vary in BOD and COD content: as with other pollutants, each sector and each process line has specific needs to be studied by testing with pilot units.

Rimozione BOD e COD nel Trattamento Acque

Removal of BOD and COD: processes and technologies

There are several technologies available for the removal of wastewater organic load related to BOD and COD. For this requirement, a number of processes can be listed.

  • Aerobic treatment. In this case, wastewater is brought into contact with oxygen to allow biochemical oxidation of organic matter.
  • Anaerobic treatment. In contrast to the previous one, this process takes place in the absence of oxygen. It involves anaerobic microorganisms, which carry out the decomposition of organic matter.
  • Chemical processes. Chemical reagents such as chlorine or hydrogen peroxide can be used to oxidize organic matter in wastewater.
  • Physical processes. When BOD/COD is in particulate form, they can be separated by gravity or mechanical separation. Sedimentation, flotation and filtration processes can then be used.

MITA technologies for removal of BOD and COD

MITA Water Technologies provides wastewater treatment technologies, both civil and industrial, for BOD and COD removal.

  • Biorulli® “biodisc” rotating biological contactors and Biocombi compact plants. A simple and efficient oxidation system that acts not only on BOD and COD, but also on nitrogen (transforming it from NH4+to NO3-). In this solution, the mass of aerobic bacteria grows attached to the media (rotating plastic discs), “feeding” and breaking down organic matter. The necessary oxygen is provided by the rotary motion of the disc, which exposes the bacteria to both sewage and air, alternately. The excess bacterial layer spontaneously detaches from the disc and is easily separated in subsequent treatments. Biorulli® are available both for installation in concrete tanks and as a monoblock in metal tanks. Biocombi®, which combine biodiscs and cloth filtration in a single compact structure, are supplied in metal tank for quick installation.
  • Dissolved air flotation units. Flotation units also act to remove COD and BOD (with possible chemical support). The circular shape of MITA’s flotation units allows the use of more functional sludge removal systems, minimizes space requirements, and makes the machine installable in settings where space is a limiting factor
  • Free-fiber cloth filters. A fraction of BOD and COD almost always has particulate form. When particularly strong BOD of COD removal performance is required, filtration may be the best choice to refine the characteristics of the treated wastewater.
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