Effective filter for BOD / DOC reduction

[pooootiqe]

Hey @Lasse

In your "optimal nitrification filter" thread you mentioned "mixed batch reactor" as a method to effectively handle BOD. I haven't found too much information online (perhaps under a different acronym?). There's another mention of "high flow rate foam filter to reduce BOD" in a different thread. Could you enlighten us on the conditions / designs one could implement at home to effectively reduce / control BOD? Is aeration of the substrate preferred like in the nitrification filter?

My ORP hovers around 300s currently. I think it was around 400s when I had a lot of live rock and rockwork in general (broke them down to clear up the vermetids) and (anecdotally) coralline algae seems to grow much quicker when I had higher ORP. Certainly haven't seen it pop up in the tank for a while. :downcast-face-with-sweat:

 

[Lasse]

Make a search with SBR waste water treatment and you will have more hits.

BOD stands for Biological Oxygen Demand and its normally counted in days - BOD7 that is common in Sweden measure the oxygen demand for a water during 7 days. In US BOD5 is more common. Why we use BOD7 instead of BOD5 is mainly because we can read it 7 the same weekday as we set it. Not need to work during the weekend :beaming-face-with-smiling-eyes:

Another acronym used among aquarist is DOC (Dissolved Organic Carbon). DOC include organic carbon that is easily used by bacteria but also organic carbon that is difficult to use by bacteria. You can say that BOD7 is that DOC that bacteria can process during 7 days. Where does this carbon ends up - a part (mostly a minor part) end up as bacteria biomass but most of it ends up as inorganic CO2 as a waste . OK - but from where comes the O2 in the formed CO2? This O2 is mostly taken from the O2 in the water. In this way you can say that BOD7 is a type of measurement that show how must organic carbon there was in the water - including organic carbon in particles.

Now - how to optimise an aerobic BOD destroyer. You need a high flow in order to get as much organic particles captured during a certain time interval and with high flow of O2 rich water you also get an optimal oxygenation of your media.

This is the biological and mechanical requirements for a high rate of conversion of organic carbon to inorganic carbon in a water - from this many different filter systems has been constructed.

IMO - the most simple filter (and also one of the more effective) is the construction below

Today I use a 2000 L/H pump - the one above is only around 800 L/H. I use 10 ppi foam mat in order to optimize the flow. This is to optimize both nitrification and BOD reduction. If the flow is too slow, organic material will collect in the filter (including dead bacterial biomass) and too much organic material in the filter will inhibit nitrification.

Note - this is rather effective for the type of DOC that is easily consumed by bacteria but for the part of DOC that is more resistant to bacterial degradation, the SBR reactor is the best. This method combines aerobic and anaerobic digestion in a batch manner and will also optimize nitrification/denitrification.

Theoretically, with a larger filter like this, you could run it in batches. Full flow with oxygen-rich water for an hour or so and then turn it off for x hours so that the filter becomes oxygen-free - then repeat the process. However - this method may involve pumping out hydrogen sulfide in batches and must in that case be combined with strong oxygenation in the receiving tank to cause oxidation of any hydrogen sulfide that is released. I have never tried this.

Sincerely Lasse

 

[pooootiqe]

Thank you Lasse - you are such a great source of knowledge!

Thanks for the clarification on the terms. It seems the difference between nitrification filter and BOD filter is mainly capturing organic particles? Would air exposure also be beneficial in this case? (trickling through coarse sponge)

The BOD destroyer shares similar appearance to GlennF's powerfilter ;) Except for the use much finer floss in that case for particle capture and disposal. I should still have a perforated PVC pipe for that purpose, will give it a try with coarse foam to see if it helps!

 

[Lasse]

Thanks for the clarification on the terms. It seems the difference between nitrification filter and BOD filter is mainly capturing organic particles? Would air exposure also be beneficial in this case? (trickling through coarse sponge)

In a trickle filter with right flow (strooooong) - the biofilm will be very thin and with a low content of dead bacteria biomass (organic carbon). This will favour (or keep) the nitrification bacteria because the heterotrophs (that´s mostly are responsible for the reduction of BOD) not getting enough organic carbon for rapid growth. However the pandemi of using fast DOC addition will favour the fast growing heterotrophs in the struggle of free space even in this case. I have sometimes played with the thought that I should construct a trickle filter where I could vary the flow and add small amount of etanol to a the flow through it. Slow flow - addition of DOC - thick bacteria film - stop the addition and let the Flood happened through the filter. The bacteria film that will be flushed out could be good food for filtration animals. The same could probably be done with help of "BOD destroyer",

For me - the difference with 30-40 ppi compared with 10 ppi is that in the first case - organic matter in the form of living and dead bacteria will accumulate in the filter. When it is full - clean and remove the organic matter (a sort of nutrient export) With the 10 ppi and a strong pump - you flush away the biofilm when it gets to thick and it will be food for filtrating animals and build biomass in an other food web.

Sincerely Lasse

 

[pooootiqe]

In a trickle filter with right flow (strooooong) - the biofilm will be very thin and with a low content of dead bacteria biomass (organic carbon). This will favour (or keep) the nitrification bacteria because the heterotrophs (that´s mostly are responsible for the reduction of BOD) not getting enough organic carbon for rapid growth. However the pandemi of using fast DOC addition will favour the fast growing heterotrophs in the struggle of free space even in this case. I have sometimes played with the thought that I should construct a trickle filter where I could vary the flow and add small amount of etanol to a the flow through it. Slow flow - addition of DOC - thick bacteria film - stop the addition and let the Flood happened through the filter. The bacteria film that will be flushed out could be good food for filtration animals. The same could probably be done with help of "BOD destroyer",

For me - the difference with 30-40 ppi compared with 10 ppi is that in the first case - organic matter in the form of living and dead bacteria will accumulate in the filter. When it is full - clean and remove the organic matter (a sort of nutrient export) With the 10 ppi and a strong pump - you flush away the biofilm when it gets to thick and it will be food for filtrating animals and build biomass in an other food web.

Sincerely Lasse

Thanks for the explanation Lasse! I have some 30ppi foam in there, guess I’ll give them a squeeze to clear up the biofilm!

I am a bit confused about the roles of the fast-DOCs in your “slow / flush” design - are they meant for nitrate reduction or actually boosts BOD reduction as well? I know some bacteria grows better with adding simple sugar even when there’s ample amount of other nutrients (yeast extract etc), is there a similar thing going on? Also is the DOC added only into the foam filter (recirculating) or into the tank water?

 

[Lasse]

I am a bit confused about the roles of the fast-DOCs in your “slow / flush” design - are they meant for nitrate reduction or actually boosts BOD reduction as well? I know some bacteria grows better with adding simple sugar even when there’s ample amount of other nutrients (yeast extract etc), is there a similar thing going on? Also is the DOC added only into the foam filter (recirculating) or into the tank water?

First - I´m not a microbial scientist. The things I know (or at least think that I know) have I been forced to get from prior jobs. some of my explanations maybe not is 100 % scientifically but at least help me to a better understanding.

IMO - in an aquarium is organic carbon a grow limited factor. Yes - there is a lot of organic carbon in organic detritus, dead organic matter and non eaten food, but much of it is hard to reach (tightly bound in hard-to-degrade organic material) The organic N and P is easier to access. In this situation - there is a shortcut - labil (or as I directly translate from Swedish - fast) DOC. Many bacteria can access this directly from the water and the existence of it speed up the bacterial growth rate. A higher grow rate - more consumption of other increases the consumption of other necessary substances such as N, P and O2 as well as many more substances. In this case O2 is interesting - a fast flow of oxygen rich water make it to be no limited in the process. As I point out in prior post - consumption of oxygen indicates microbial decomposition of organic matter or with other words speed up the mineralization of organic matter. If the flow of oxygenated water is so low that the dissolved oxygen becomes limiting for oxygen-dependent growth of bacteria - many bacteria has another trick in order to survive - they switch to anaerobic break down with help of NO3 (if present) in the in cellular respiration. In aerobic cellular respiration - H is the counterpart to O2 in the process - in anaerobic cellular respiration with NO3 present - DOC is the counterpart.

Try to sum it up. DOC has many tasks in this theoretical slow/stop/flush design.
1. To speed up the breakdown process
2. hence create an anaerobic environment when oxygen is limited for growth
3, Serve as a counterpart to NO3 in the denitrification process

However - IMO - the DOC should be added in the inlet to the filter and not so much per time unit that it is coming out in the water column. It should be consumed in the filter. If the denitrification should be significant - it probably need a rather large volume or rather much DOC and a higher start/stop frequency. I have not tested this but in my aquarium there is a reversed flow DSB in my refugium build on these principles and it work well at least according to denitrification. But to be honest - I don't know if this is because my theories are correct or if I encountered a rather unknown process - anammox - but I can control my NO3 level with the amount of ethanol added (DOC). I do not run flow/stop in this process - I have a continuous flow through the sand bed

https://www.reef2reef.com/threads/lasses-dream-build.246188/#post-2891811
Sincerely Lasse