If you have a microbiological system where you have a heterogeneous source of electron donors but water cannot be one of them (that is so, there is no algae nor cyanobacteria activity), how can total COD increase with concomitant metabolic activity? All the electron donors but water can provide COD to the system? Is there any electron donor other than water that have not COD?
This is a strange question. Chemical oxygen demand (COD) has nothing to do with microbial activity in the system. COD is a measure of chemical oxidation not microbial oxidation of susceptible matter. Most wastes will produce a COD level greater than the BOD level of the same waste typically due to the inability of the microbial seed to attack some components o fhe waste. In the case of COD, the dichromate ion is the electron acceptor and sulfuric acid provides strong hydrolysis of complex organic matter..
Hi Richard, oxygen is not an electron donor, but an electron acceptor, so consumption of oxygen causes the contrary effect, that is so, a decrease in total COD of the system
Dear Richard Unz. It is true that COD is not directly related with microbial activity (BOD is the parameter), but a good way for estimating electron balance in a microbial system is measuring COD variation since you are measuring increments or diminishes, which are relative values directly related with the microbial activity. There are some systems where the total COD is decreased by the microbial activity (e.g. aerobic processes), some others where the total COD increases (autotrophic growth with water as an electron donor) and other where the total COD remains constant (any kind of fermentation). I am trying to look for a system where the total COD increases after microbial activity but the microbial community is not using water as an electron donor.
Dear Daniel,
Is there any chance that there is a source of reductive power in your system that is solid, that you do not measure at first and that progressively biochemically reacts? Some kind of imobilized minerals? Otherwise, an electron input from a cathode could be responsible for such a phenomenon.
Hope this could help,
Cheers
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