Bacteria vs. algae for N&P reduction

[dzhuo]

Posted in the reef discussion forum but not getting much response. Let's see if the more advanced reefers knows about this.

I have been closely following most of the major bio-pellet threads for a few months now and I don't seem to recall discussion of bacteria vs. algae in terms of efficiency in N&P reduction. Are there significant advantage of using bacteria for N&P reduction? Are they particularly more efficient? If so, at what rate? Why don't we just grow chaeto (again for N&P reduction) like we used to and just call it a day?

It seems like bio-pellet is still somewhat of a hit and miss (most people do seem to have at least some success tho) with the potential of bacteria or cyano bloom while chaeto is almost risk free (and cheap).

 

[waldomas]

Assuming algae needs light to grow / export, and a bio-pellet reactor needs flow through the media, wouldn't overall efficiency be determined by the equipment?

 

[dzhuo]

Let's assume ideal environment. Obviously, if there isn't sufficient light for the algae to grow then the comparison isn't fair. Similarly for bacteria, if there isn't enough carbon source for them to eat, the colony won't be able to reproduce and grow.

Assuming we have tank A which is able to grow chaeto successfully. You take the chaeto out, put a reactor in with recommended amount of bio-pellet, would the (mature) bacteria colony in the reactor be able to continue to maintain the N&P level previously achieved by chaeto?

 

[waldomas]

Of course! Sorry.

 

[JoeCreature]

Probably boils down to the C:N ratio of the macroalgae vs. a particular species of bacteria and then the maximal growth rates of each respectively.

Which leads to the next questions:
-Which macro grows fastest and has the best C:N conversion ratio?
-Which bacteria species "ditto" ?

Then its just a math equation

Thats oversimplified but given nothing is limiting and the ultimate goal is max N & P removal.

 

[waldomas]

I mean... I think macro-algae would enable greater bio-diversity which could better "weather" the minor instabilties present in all our closed systems.
Of course proper precautions would need to be taken to aid in maximum growth / nutrient export (nutrient uptake, lighting schedule, harvest, etc.).



Errrr....yeah, what he ^^ said.

 

[dzhuo]

Probably boils down to the C:N ratio of the macroalgae vs. a particular species of bacteria and then the maximal growth rates of each respectively.

Good thinking but I really don't want to over complicated things. Most of us keep very similar tank (LR, sand, corals, fish, skimmer, light etc) as a closed system so let's assume every tank eventually leads to a very limited number of bacterial strains. Let's assume the addition of these commercially available bio-pellets does not promote extra strains but simply provide extra carbon source for them to multiply in great number. In other word, adding bio-pellets does not introduce greater bio-diversity, only increase the bacteria colonies already present in our tank. If that's not true, please let us know.

As for algae, let's just say it's chaeto which most people use.

 

[dzhuo]

Anyone else have thoughts on this?

 

[Amphiprionocellaris]

As far as the efficiency of the C:N ratio, it tends to hover around 106:16:1; deviations if any are going to be minor and not much of a determinant in which one is "better." What is really going to be key is the speed of growth, in which case bacteria, with their much higher turnover, will have a much faster uptake. However, in terms of actual removal, the major factor is how easily you can remove the organisms from the tank. With that being the case, algae would be better, because bacteria are largely going to sit in the water column or sand bed while algae are relatively easy to remove from the system.

What complicates the matter is the fact that simple growth isn't the only effect of nutrient addition. Denitrification is also limited by carbon (or nitrate, but we'll assume nitrate isn't limiting for now); DOM addition not only provides more material for use in denitrification, but it also increases rates of aerobic degradation, which can in turn increase rates of denitrification. That doesn't really answer your question directly, but the point is to keep in mind that DOM addition doesn't simply function via increased growth rates, so biopellet addition may increase nitrate removal in a very roundabout way that has nothing to do with the removal efficiency of bacteria or algae.

 

[JoeCreature]

+1

The main problem with studying biology is there is never a simple 1:1 conversion.

Bacteria are great for Phos removal because bacteria are little ATP (Adenosine Tri-Phosphate) factories. The goal of a bacteria is to consume and divide, thus making more Phos sucking ATP factories.

At the cellular level using the basic Redfield ratio for C:N of 106:16:1, both bacteria and macroalgae require 1 P per 16 N.

In a hypothetical simple system it would just be a series of plug and play equations to figure out which train reaches Chicago first. However, as Amphiprion eluded to it is much more complex than that. How does one go about calculating the increased rugosity and and surface area of the macroalgae? Because this will provide additional substrate for more benthic bacteria colonization.

So which method is better? Simple answer: both in tandem...........the key is balance Daniel-sahn

 

[Amphiprion]

Organic carbon is truly, rarely limiting in aquariums, especially reefs. Also, keep in mind that the Redfield ratios primarily apply to phytoplankton, so are only a good indicator for some algae. Some organisms can overstep this ratio, sometimes considerably. Lastly, RRs are true mostly in the ocean. The foods and inputs in aquaria can skew this. There can be at least have some degree of adherence in terms of algae, though.

In terms of actual reduction times, that all varies on the ideal conditions for the target organisms. Everyone's experience will probably vary as a result. In my setup, I made ideal conditions for algae in the form of a turf scrubber. The N and P reduction time for me was far faster than bacterial methods I had used in the past. However, I never used more ideal conditions for bacteria, such as reactors, sponges, etc. in a dark area, such as a sump. I would say, however, that in terms of overall potential for lowering N and P, bacterial methods would likely have the advantage.

Risks, I suppose, are another thing altogether. Algal methods are likely far safer in most cases (assuming the "better" species/types of algae are chosen). That being said, there are still plenty of folks who've had no issues with bacterial methods.

 

[Amphiprionocellaris]

Organic carbon is truly, rarely limiting in aquariums, especially reefs.

I disagree. Although DOM may not be limiting per se as far as actual growth, if there is insufficient DOM in the tank, then it's possible for sediments/live rock to remain entirely aerobic (because DOM consumption is not sufficient to exhaust oxygen and allow a changeover to nitrate for a terminal electron acceptor). In these cases, dosing organics can be a big help, just simply not in the way that it seems most aquarists think of it. If an aquarium has persistently high nitrates despite low feeding, I would suspect DOM limitation as a major factor. Of course, that doesn't do anything for phosphate, as this deals only with nitrates.

Now as far as actual removal efficiencies, regardless of how closely aquaria adhere to Redfield (which we could debate for quite a while given the lack of solid research), I think the most important thing to consider is ease of removal from the system. Even if bacteria are more efficient at nutrient removal, they aren't necessarily an efficient sink because there's not an easy and effective way to remove them from the system. Algae, on the other hand, are ideal in this regard.

It really depends on what you're trying to do. If you go for growth and removal as a sink for nutrients, then algae would be IMO the way to go because you can easily remove them from the system. However, if you're trying to increase the metabolism of nitrates into free nitrogen gas, then dosing DOM can help if there is insufficient organic matter to promote hypoxia in the sediment.

 

[dzhuo]

It really depends on what you're trying to do.

I have a fairly simple objective in mind: Keep N&P close to environment favor SPS grow. I am fairly fascinated with the early development of bio-pellet and the whole bacteria driven system to maintain N&P in a closed loop system. I have yet to jump the gun because of the risks (bacteria bloom, oxygen level, pH and CO2 changes, colony crash, etc) and cost (powerful skimmer, carbon source, media, pump, etc) associated with running such a system while it's not clear to me how much advantage does it really have over algae (which is a lot less risky and more cost effective).

It would be nice to see actual scientific prove comparing the 2 types of system but I understand there might not be one. As I mention earlier, since most of us run almost identical system (same salt, same type of skimmer, feed about the same type of food, host the same type of corals and fish, use RO/DI and keep most major parameters close to NSW), I have reason to believe virtually all tanks are the same when it goes down to the bacteria level of the ecosystem. If we theorize such a typical close system for test and you split a tank into 2 half. In one half, you throw a handful of chaeto and clap a light on top of it. In the other half, you simply add a bio-pellet reactor with mature bacteria colony. Since the 2 half tank starts with equal amount of N&P, at the end of the 1 week cycle, which half of the tank has less N&P?

Lots of interesting discussion but what's DOM?

 

[Amphiprionocellaris]

First off, DOM = Dissolved Organic Matter, which is a proxy for carbon. I'm a marine scientist, so it's hard to shake the habit of just using "DOM."

As I mention earlier, since most of us run almost identical system (same salt, same type of skimmer, feed about the same type of food, host the same type of corals and fish, use RO/DI and keep most major parameters close to NSW), I have reason to believe virtually all tanks are the same when it goes down to the bacteria level of the ecosystem.

Here, I would disagree, because feeding regimens can vary vastly between systems, and the amount of DOM input (in the form of food) is one of the major determinants in a system's characteristics. That's likely why some people have great success with the "bacterial" method and others don't; it all depends on which parts of the nitrogen cycle are operating (low-DOM systems can have nitrate buildup because denitrification can't take place). All that said, algae would be better for your goal because it's easier to remove. The bacteria may remove N/P from the water column faster, but the N/P still stays in the tank to a larger degree than if you remove it in the form of algae (because it's harder to efficiently remove bacteria).

 

[syrinx]

I agree with above- esp the removal of algae being easier. Also there is no dosing or calculating required-you are not going to get slimed or have other issues with algae.

 

[dzhuo]

First off, DOM = Dissolved Organic Matter, which is a proxy for carbon. I'm a marine scientist, so it's hard to shake the habit of just using "DOM."

That's part of the reason why this board is great with actual scientist actively involving in the hobby. I have done a little more reading both on algae and bacteria and realize algae (especially different one) has very specific need in order to grow which bacteria seems more forgiving. While we all know algae needs N&P to live, it actually requires a certain level of N&P in order to grow and thrive. This seems to be the clear difference between algae and bacteria. With algae, your system can have enough N&P so it continue to live but not enough to sustain continuous grow. When this happen, it could mislead hobbyist to believe there isn't N&P. With bacteria, it seems like they are able to continuously absorb N&P as long as there is also C present.

I am having a feeling most people who uses chaeto exclusively fall into this category because chaeto needs substantial N&P for grow, once it drives these down after the initial grow sprout; grow stops so further N&P uptake also stop. If they switch to bacteria, they will then continue to see N&P reduction. I believe if we don't monopolize the sump with only chaeto, we could see different result.

Does this make sense?

 

[Amphiprion]

I disagree. Although DOM may not be limiting per se as far as actual growth, if there is insufficient DOM in the tank, then it's possible for sediments/live rock to remain entirely aerobic (because DOM consumption is not sufficient to exhaust oxygen and allow a changeover to nitrate for a terminal electron acceptor). In these cases, dosing organics can be a big help, just simply not in the way that it seems most aquarists think of it. If an aquarium has persistently high nitrates despite low feeding, I would suspect DOM limitation as a major factor. Of course, that doesn't do anything for phosphate, as this deals only with nitrates.

Now as far as actual removal efficiencies, regardless of how closely aquaria adhere to Redfield (which we could debate for quite a while given the lack of solid research), I think the most important thing to consider is ease of removal from the system. Even if bacteria are more efficient at nutrient removal, they aren't necessarily an efficient sink because there's not an easy and effective way to remove them from the system. Algae, on the other hand, are ideal in this regard.

It really depends on what you're trying to do. If you go for growth and removal as a sink for nutrients, then algae would be IMO the way to go because you can easily remove them from the system. However, if you're trying to increase the metabolism of nitrates into free nitrogen gas, then dosing DOM can help if there is insufficient organic matter to promote hypoxia in the sediment.

Agreed for the most part. On organic carbon, keep in mind that corals also provide a glut of it every single day, all the time. Food input, while relevant, isn't the only source Coral mucus is extremely carbohydrate rich and is how they export excess C that they receive from zooxanthellae and photosynthesis. Algae are also a large source of this in aquariums. I just think the odds of it being limited (except in areas of extraordinarily small turnovers) are slim given all the various sources. I think where added sources help bacteria isn't in that organic C is limited, but rather a more readily metabolized source is limited. That is where I feel one of the whole ideas for organic carbon dosing is somewhat flawed, but that is a different story.

 

[Amphiprionocellaris]

Well algae can be pretty non-demanding, too, and they are the primary source of the Redfield Ratio (so we have a good handle on the conditions in which they thrive), but you are right about the benefit of diversity. One thing that we haven't mentioned at all, though, is the reef itself. Many aquarists seem to be of the mindset that we must eliminate all nitrate and phosphate, but this ignores the fact that corals (and their symbionts) and other major reef critters need N/P as well. Healthy growth of the ecosystem as a whole will also drive down N/P levels (for instance, my reefs have 0 detectable N/P, and I employ neither bacteria or algae in the sense we're discussing here). Using, and "feeding", bacteria and algae is way more complicated than simply encouraging their growth in the hope that they'll lock up nutrients.

It is my hypothesis that we actually starve the majority of tanks, so the reason we see benefits with bacteria dosing/vodka/etc is that we increase the energy flow through the system and allow corals to reach their maximum potential. It can also help increase the biodiversity of the system (which is maintained by high energy flow), which in turn increases the system's capacity to process waste. The system then likely reaches some sort of tipping point at which the ecosystem is able to thrive and grow, which dramatically increases nutrient uptake rates. This is, of course, hypothetical, though I am almost done with an energy budget model that will take some of the guesswork out of the ecosystem approach.

So, in summary, methods that encourage the growth of particular algae or bacteria work not simply by the benefits of growth, but through the basic fact that the whole ecosystem is healthier. However, in cases wherein the system already possesses a healthy, non-limited ecosystem, bacteria dosing can backfire if it increases the nutrient import so that there is a buildup of said nutrients; it is literally all about balance!

 

[Amphiprionocellaris]

I just think the odds of it being limited (except in areas of extraordinarily small turnovers) are slim given all the various sources. I think where added sources help bacteria isn't in that organic C is limited, but rather a more readily metabolized source is limited. That is where I feel one of the whole ideas for organic carbon dosing is somewhat flawed, but that is a different story.

I don't think I've done a great job of explaining this. Carbon is likely not limiting for growth, but growth is not the largest sink of nitrogen on the coral reef, denitrification is. But denitrification only occurs where there is a source of OM available for that metabolic pathway. If there are low levels of DOM that make it to the sediment, all of it will be consumed aerobically with none left over for denitrification. This occurs in general via the rate law R1 = k*DOM*[O2]/([O2] +KmO2), where KmO2 is the half-saturation constant of oxygen and is around 20 uM (normal O2 concentrations are 220uM). The value of k can vary (and has to do with the availability of the carbon source that you mentioned), but for many aquarium food sources, it can be on the order of 1e-5 mol/(m^3*s) (which is really fast). Since we're talking the math, I'll say that the rate for denitrification is similar: R2 = (k*DOM - R1)*[NO3]/([NO3]+KmNO3). What this basically means is that DOM left over once oxygen is depleted can then be used in denitrification.

Ok, that's all well and good, but it's so far pretty meaningless. Let's consider our sediment, where oxygen and DOM both diffuse at generally the same rate (they don't quite, but it's pretty close). If the oxygen concentration is much higher than the DOM concentration, then the value of R1 is basically always going to be k*DOM (because [O2] is much larger than KmO2 so that [O2]/([O2]+KmO2 = 1); all the DOM will be consumed aerobically, which ends up producing nitrate as an end product. If, on the other hand, DOM is a good bit higher than [O2], then R1 will be less than k*DOM when oxygen levels get low, which means there is now DOM left over for denitrification to use. That's what I mean by saying DOM is limiting, and I've run a number of model simulations to test the idea; sure enough, under light feeding conditions, nitrate reduction never happens. The model was run assuming a constant input of 1 g of food into a 40 G tank, which is a lot (in the budget, coral production is largely contained within the colony...it's a simplifying assumption), and the sand bed remained entirely oxic.

Now, is the picture that simple? Lord no, and I'm still working on calculating it out without frying my MacPro. Bioturbation (the physical movement of OM) plays a huge role, as does production within the tank. But given the potential for huge, effective skimmers and organics removal, it's not a stretch to see how DOM can indeed limit denitrification. And then the picture gets still more complicated when we consider the energy budget as a whole. Dosing carbon can be an excellent thing to do, it just needs to be done within a framework of knowing how the ecosystem works, which is something I'm working on modeling.

Hopefully I didn't get overly technical, but this is my research, so let me know if you have questions.

 

[Amphiprion]

That makes better sense of what you were trying to say. I think a healthy, heavily-fed system with advection, bioturbation, as you pointed out, and other mechanical/chemical processes would affect that model substantially, though. And, of course, lack of proper energy input causes plenty of issues, which is a fact that has resurfaced even more so recently--especially in light of highly efficient export mechanisms. I see a recurring trend of people removing everything and then trying to add it back, which I think this presents a great example of. Then again, in the absence of auxiliary forms of filtration, I know that most systems can adequately utilize most of the potential input that is added--they just aren't often given the chance. I suppose I didn't clarify that I was considering more ideal situations in what I was attempting to explain, myself. I wasn't expecting to have to dip back into kinetics, either . I suppose I have to utilize my biochem eventually, lol.