Reef Central Online Community - View Single Post - Reflects before you begin dosing carbohydrates

Belgian Anthias · 01/04/2018, 03:24 AM

A lot of heterotrops and autotrophs ( denitrifiers) have also or only a transport system for nitrate take up for respiration. This respiratory Nar system is triggered by nitrate, suppressed by oxygen and is not sensitive for ammonia. http://www.baharini.eu/baharini/doku...traat_reductie

In most normal biofilms surrounded by oxygen saturated seawater denitrification takes place. Oxygen is consumed in the outer layers of the film in a way not enough oxygen can reach the middle and lower zones . In normal circumstances, about 1/3 of the oxygen is used by heterotrops and 2/3 for nitrification, +- 1/3 of the ammonia is reduced by heterotrops and +-2/3 by autotrops.
An oxygen minimum zone ( OMZ) is created within the film, ideal for autotrophe denitrification. The Nar system of autotrop denitrifiers may be triggered at an oxygen level above 0,5 ppm. Autotroph denitrification is limited because of the limited availability of usable sulphur provided by HS production within the film. This limited autotrop denitrification is necessary for recycling HS formed due to decay within the film, back to sulphur or sulphate. In the sub layers anoxic conditions may be created and heterotroph denitrification may be activated. Most heterotrophs need an oxygen level lower as 0,5 ppm to trigger the Nar system. The heterotroph denitrification is limited by the available organic carbon provided by normal decay within the biofilm and the limited anoxic space. http://www.baharini.eu/baharini/doku...chemie:biofilm

When a high C:N ratio is maintained by carbohydrate dosing most ammonia is assimilated in the water column but also in the biofilm. The structure of the biofilm will change drastically as the nitrifiers are overgrown by the very fast growing heterotrops and lose the battle for oxygen. As the nitrifiers are suppressed the ammonia they normally use is available for assimilation. Due to the very high growth and oxygen consumption in and on the outer layers of the film the OMZ zone may become anoxic making more heterotroph denitrification possible. When not enough nitrate is available, sulphate will be used.
After some time the biodilm will become mostly heterotropic due to the competition for nitrate in the low oxygen zone and the high decay rate providing organics. HS will not be recycled any more within the biofilm but oxidised when leaving the biofilm producing sulphate.
Autotrophs are outcompeted! The autotrophic ammonia reduction potential which was build up is lost.

An other biologic balance will be found and the heterotroph growth may be matched to keep this balance by maintaining a balancing C:N ratio. This means regular and continues dosing.

More nitrate may be removed effectively from the system by increased heterotroph denitrification.

Keeping a low slightly increased C:N ratio may induce a higher mixotroph denitrification rate within a normal nitrifying biofilm. This can also be done by providing some more usable sulphur to the biofilm , this way eliminating daily matched dosing. http://www.baharini.eu/baharini/doku...ter#spc_system

For a biofilm in a very low oxygen environment ( live rock, DSB) this scenario may be a bit different. HS can not be oxidised when leaving the biofilm, may build up and be released as H2S gas.

01/04/2018, 03:24 AM	#40
Belgian Anthias Registered Member Join Date: Oct 2009 Location: Belgium Posts: 608	Respiratory Nar system A lot of heterotrops and autotrophs ( denitrifiers) have also or only a transport system for nitrate take up for respiration. This respiratory Nar system is triggered by nitrate, suppressed by oxygen and is not sensitive for ammonia. http://www.baharini.eu/baharini/doku...traat_reductie In most normal biofilms surrounded by oxygen saturated seawater denitrification takes place. Oxygen is consumed in the outer layers of the film in a way not enough oxygen can reach the middle and lower zones . In normal circumstances, about 1/3 of the oxygen is used by heterotrops and 2/3 for nitrification, +- 1/3 of the ammonia is reduced by heterotrops and +-2/3 by autotrops. An oxygen minimum zone ( OMZ) is created within the film, ideal for autotrophe denitrification. The Nar system of autotrop denitrifiers may be triggered at an oxygen level above 0,5 ppm. Autotroph denitrification is limited because of the limited availability of usable sulphur provided by HS production within the film. This limited autotrop denitrification is necessary for recycling HS formed due to decay within the film, back to sulphur or sulphate. In the sub layers anoxic conditions may be created and heterotroph denitrification may be activated. Most heterotrophs need an oxygen level lower as 0,5 ppm to trigger the Nar system. The heterotroph denitrification is limited by the available organic carbon provided by normal decay within the biofilm and the limited anoxic space. http://www.baharini.eu/baharini/doku...chemie:biofilm When a high C:N ratio is maintained by carbohydrate dosing most ammonia is assimilated in the water column but also in the biofilm. The structure of the biofilm will change drastically as the nitrifiers are overgrown by the very fast growing heterotrops and lose the battle for oxygen. As the nitrifiers are suppressed the ammonia they normally use is available for assimilation. Due to the very high growth and oxygen consumption in and on the outer layers of the film the OMZ zone may become anoxic making more heterotroph denitrification possible. When not enough nitrate is available, sulphate will be used. After some time the biodilm will become mostly heterotropic due to the competition for nitrate in the low oxygen zone and the high decay rate providing organics. HS will not be recycled any more within the biofilm but oxidised when leaving the biofilm producing sulphate. Autotrophs are outcompeted! The autotrophic ammonia reduction potential which was build up is lost. An other biologic balance will be found and the heterotroph growth may be matched to keep this balance by maintaining a balancing C:N ratio. This means regular and continues dosing. More nitrate may be removed effectively from the system by increased heterotroph denitrification. Keeping a low slightly increased C:N ratio may induce a higher mixotroph denitrification rate within a normal nitrifying biofilm. This can also be done by providing some more usable sulphur to the biofilm , this way eliminating daily matched dosing. http://www.baharini.eu/baharini/doku...ter#spc_system For a biofilm in a very low oxygen environment ( live rock, DSB) this scenario may be a bit different. HS can not be oxidised when leaving the biofilm, may build up and be released as H2S gas.