I'm curious how bacteria process nutrients or ammonia. How fast is this reaction? Is bacteria pull those nutrient out the water instantly or it takes some time for this to happen? In a frag system there is no live rock in display tank and all the bio media or live rock is in sump area. In this situation, is faster sump turn over more beneficial to lower nutrients(carbon dosing) or slower(more pass or more contact time? ? Thanks
Good questions.
So bacteria processes nutrients in many different ways, but we can largely split this into two categories - those respiratory-related, and those growth-related. Respiratory-related processes essentially relies on the transfer of electrons from one compound to another to generate energy. For nitrifiers, they can transfer electrons from ammonia and nitrite to oxygen, a process that occurs so long as the relevant molecules are present, although the speed itself is not limited due to being governed by a number of biotic and abiotic processes. That is why when you first start your cycle, ammonia- and nitrite-oxidation can begin relatively slowly, but then ramp up as there are more and more nitrifiers available. For example, this study:
https://pubmed.ncbi.nlm.nih.gov/11228996/ observed an ammonia-oxidation rate of 0.6 mg/L/h NH4-N per 100 million
Nitrosomonas cells in pure culture, though of course this can be very different 'in practice'.
Ammonia is also uptaken by all lifeforms in one way or another, as they make up certain essential amino acids required by all life as far as we know. This means that ammonia is directly incorporated into cellular components, however this process is limited as once there are enough of these components, ammonia assimilation slows down or stops.
This is why there is the whole debate over what microbes we'd actually want in our aquariums. Some people say that any bacteria will do fine, even those that enter the aquarium from the air or wherever. You can have a lot of these bacteria initially consuming a lot of ammonia as they grow, but then the process slows down or stops completely as the populations of these bacteria reach a limit, and suddenly boom ammonia consumption significantly drops. Nitrifiers are not limited by this, because even if they reach a population peak, they can still continuously oxidize ammonia.
This is also a reason why a lot of people would not recommend cycling with something like Microbacter7, as that contains microbes that are not lithotrophic nitrifiers that may outcompete the lithotrophic nitrifiers we want for the same habitat.
As for the flow rate question, faster is better. There is not really an amount of 'lingering' time needed for microbes to take action. The chemical reactions happen fast enough that you can't really ever have a flow rate be 'too fast'.
