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COD REDUCTION
The COD or Chemical Demand of Oxygen is the amount of oxygen necessary to oxidize all the organic and oxidized matter present in residual water. It is therefore a representative measurement of the organic contamination of an effluent and a parameter to control under the different spills norms that provide us a very real idea of the degree of toxicity of the spill. There are different forms to diminish the COD like the physical-chemistries treatments, the electrocoagulation and ozone.
The BOD or Biological Demand of Oxygen is the amount of oxygen that the microorganisms need to degrade the existing biodegradable organic matter in residual water. It is therefore a measurement of the organic component that can be degraded by biological process. It is possible to be said therefore that the BOD represents the amount of biodegradable organic matter and the COD represents the biodegradable organic matter and the no biodegradable one.
It is necessary, therefore, to control these parameters simultaneously to assure a good quality spill at the same time we fulfilled the legal norms without creating environmental alterations or putting in danger our ecosystem. In order to reduce the BOD of spill, the most suitable are the biological process where we can have different alternatives.
The aerobic process is based on microorganisms that (in oxygen presence) transform the organic matter in gas and new cellular matter which use for their own growth and reproduction.
Another type of process in the degradation of the organic matter is the anaerobic process, in this case in total oxygen absence. Through these treatments, gases (like methane) are obtained and they can be taken for energetic uses.
However, another type of physical-chemistries treatments can usually be necessary to diminish the content of no biodegradable organic matter. Inside these treatments there are a great variety of possibilities:
With coagulation and flocculation process we are able to destabilize the laid-down loads of the organic matter in suspension at the same time we form small floccules of organic matter which are easily filterable or sedimentables.
The ventilation reactors help to obtain a better oxidation as a complement of coagulation and flocculation process and to diminish even COD in some cases.
In many occasions, this type of treatments is not absolutely effective in the diminution of the chemical demand of oxygen, due to the own nature of the organic matter that contains the water, or, by the high values of COD that avoid to get the adapted reductions necessary to reach the spill parameters. For these cases it is necessary to resort to other alternative process.
The treatment with ozone is very effective in the oxidation of organic matter. Ozone is an allotropic oxygen form that is distinguishes of oxygen common because the molecule is formed by three atoms instead of two. This confers a powerful oxidant power that's why it is an effective treatment for reducing COD and BOD. In order to make the treatment to reduce COD, the most appropriate is to determine correctly the proportions to the minimum ozone production necessary as well as the average time of contact to obtain the predicted elimination of BOD. In function of the process, space, yields and other factors the installation can be made of several forms. Injection of ozone by a diffuser in a contact tank, by Venturi in recirculation, etc. Hidritec makes researching tests to obtain the optimal yield of quality and price in facilities of reduction of COD by a correct initial exposition of the system with concrete data of percentage of BOD reduction. The treatment with ozone, really, diminishes the laid-down load present in the water. It eliminates odour and colour and it produces a total disinfection of the microorganisms that can be present.
Another alternative to get a good yield of diminution of COD is the electrocoagulation treatment.
The electrocoagulation process is very similar to a typical chemical coagulation treatment but using electrical energy. Both processes have the objective of the destabilization of colloids contained in water and they are different in the addition way of the reagent: in conventional coagulation the reagent is added as salt and in electrocoagulación it is generated from a metal.
It is possible to define the electrocoagulation like an electrochemical process in which the existing colloidal matter in residual water is grouped thank to compounds which come from the dissolution of an anode. This produces its separation of the water by conventional techniques. As a consequence of their dissolution, the anodes are disappearing as the treatment goes by, until it is necessary its replacement (sacrifice anode). By this system it can be got high performances in the elimination of heavy metals, fats and oils, phenols, solids in suspension and colloids at the same time that virus, bacteria and microorganisms are eliminated. Hidritec, like in the purification with ozone, makes researching tests for the reduction of COD treatments by the use of electroionization techniques.
