Fish waste in algae scrubber

[amalaqua]

I am running FW tank with discus with algae scrubber as only filter. Every thing fine but fish waste seems to accumulate at bottom. How it is managed? Whether it is a concern or not. How scrubber is dealing with this?

[SantaMonica]

Fish waste is food particles for smaller animals, just like in lakes. There are no clear lakes; all waste (food particles) fall to the bottom to be eaten by other animals.

So you can just leave it to collect, if you want the natural lake look. Or you can siphon it out if you want the non-natural clean aquarium look. The scrubber does not care; it only absorbs nutrients, not food particles.

If you want to leave it, add a layer of large gravel so that the particles will fall into it; then add more clean up crew.

[amwassil]

This response confuses me somewhat. As far as I am aware, no 'smaller animals' eat fish poop. Even aquatic snails won't eat fish poop and the snails produce lots more poop of their own. Also, in a natural environment there is a continual flow of clean oxygenated water (usually) which helps to oxidize many breakdown products in the water and there are many micro-organisms that do not exist in the artificial environment of an aquarium. That said, I appreciate that once the poop starts breaking down into various organic compounds the algae will consume the nutrients. Are you saying that the algae will consume everything that might be detrimental as it slowly decays on the bottom of the tank and/or bacteria will eventually render it into something innocuous? Who exactly are you referring to as the 'clean up crew'? I have used Nutrafin 'Waste Control' and Laguna 'Bio Sludge Control' in my turtle tank to try to liquefy solid waste so it can get into the biological filter. Both those products claim to contain bacteria that do the job, but I've found that little if any solid turtle waste actually gets dissolved by this stuff. Adding a layer of sand or gravel to the bottom of an aquarium runs the risk of providing a habitat for anaerobic bacteria that can produce gases poisonous to fish even at low levels.

I'm sure that a lot of us who spend time cleaning debris from our aquariums would like to know we don't have to do this. Please advise. Thanks.

Michael

[amalaqua]

Yes sir, I spend lot of time to clean debris accumulated at the bottom of the tank. So far algae problem in the display tank is concerned that has been solved by ATS. But now for the fish waste I am thinking of adding some cleaning pump ( As cleaning crew ). This pump will suck the fish waste through some filter medis ( Sponge etc ) and clean water will flow back to the tank water. Only thing I reqire cleaning of the filter media and inintially I got result also. Of course it is a very simple thing. But no other option I can think. If any body can help it will be fine. I am waiting. Pl. help me urgently. Thanks.

[SantaMonica]

Filter sock is fine if you want to use it.

Yes, a lot of clean up crew such as hermits eat fish waste. That's what clean up crew do, otherwise they are not a good crew. And on a reef, almost all the oxygen comes from the algae, not "water changes". Most nutrients stay locked up and recycled in the reef, and do not interact with the ocean water. Nutrients can't travel for more than a few meters before being absorbed by algae.

Algae do not consume organic nutrients (i.e., food particles and DOC); only inorganic nutrients. So yes, the algae will consume all that is needed to be removed; that's how the natural systems work... algae does all the cleaning. All of it. My tanks have gone years with only algal filtering.

Gravel will not cause H2S; that would require very fine deep sand, or mud.

[amwassil]

Thanks. How would one go about replicating that in a fresh water tank? In the natural environment virtually all bodies of fresh water have a fairly steady flow through of clean, oxygenated water. Truly stagnant ponds are not very productive other than bacteria and much of that ends up being anaerobic producing methane. I haven't yet discovered a fresh water 'small animal' that eats anyone's poop other than bacteria. Maybe I missed something, I hope. ;-)

Currently, I use a small Eheim classic canister as a water vacuum system to clean debris out of both my turtle and fish tanks. This works, but it's 'work' and I have to clean the sponges in the canister once in a while to keep it vacuuming. Unfortunately, the turtles would likely see any 'small animals' as fast food. I can't even keep snails with those guys.

[SantaMonica]

Try a Triops:
http://www.petfish.net/kb/entry/188/

Or, if you just let the waste pile up, the microbes will explode and eat the detritus as fast as it develops. You could just keep is all in the gravel, or under a grating. I have no CUC in two FW tanks, and the waste just disappears on it's own.,

[amwassil]

Thanks for the info! What is 'CUC'?

[Oct03] CUC = Clean Up Crew?

[SantaMonica]

Yes

[amwassil]

I bought a triops kit and it arrived yesterday. Those guys only live 30-60 days so that means a breeding cycle! I'll report my adventures as they occur. Thanks again for the info.

[perlboy]

Hi amwassil. Saw you name in this thread and thought I'd offer a solution.

Fish poop, otherwise known as solids, is bad because it decays to ammonia. Ammonia must be removed via the nitrification process by some means, as it can be toxic. Timmons in Recirculating Aquaculture, 2007, recommends keeping NH3 < 3.0 ppm. I know algae scrubbers prefer to do that job with algae scrubbers (pun intended) but there are many types of biofilters that do that job IMO better (I’ll defend that point in a moment, but first…). My preferred biofilter is an MBBR.

Full disclosure: I have never maintained a marine display aquarium. My experience is with commercial aquaculture, tilapia (a fresh water species) and Pacific white shrimp (a salt-water species.)

It is standard procedure in aquaculture applications to remove solids with a settling tank. Some call this device a clarifier. It is a simple device, easy and cheap to make and relatively easy to maintain. An effective example can be made from a 5-gal plastic bucket. Purpose, to reduce the load on the biofilter by removing suspended solids (fish poop and uneaten food.)

A settling tank introduces water containing solids (we call this a slurry) at the top but directed to the bottom. This is done through a baffle. Suppose your input pipe is 1 in. A 3” or 4” piece of PVC, its top level with the top of the clarifier, makes a good baffle. I hang mine by screwing ½” PVC to the outside of the baffle (stainless steel screws) and drilling holes in the bucket (slightly higher than the output port) to hold these support tubes. Solids are denser than water so they settle to the bottom. Clear water (that is directed to the biofilter) flows out of the clarifier near the top. It is useful to suspend some sort of flexible netting at the midpoint of the clarifier to keep the solids from rising back to the top. There should be as little turbulence as possible inside a clarifier so this is not the place to put an airstone or diffuser. What we call sludge is dumped from the clarifier through a bottom drain. A gravity blast of 1-2 gals from a 5-gal bucket is sufficient. The sludge can be dried in the sun and then used as fertilizer, since it is rich in organic matter. A useful rule of thumb, Van Gorder, Small Scale Aquaculture, 2000, when sizing a clarifier is to allow 5.5% of tank volume. How often one dumps a clarifier is a function of how fast they fill. In aquaculture we prefer translucent tanks so one can see how much solids is building up. Translucent cone or dome bottom tanks are ideal but considerably more expensive than plastic buckets, typically 4x more expensive in 5-gal size. A 5-gal bucket should be good for up to a 90 gal aquarium, and of course, there are 6 and 7-gal buckets readily available, and you can run two or more in parallel.

You want the flow through a clarifier as slow as possible to provide the maximum time for the solids to settle. Timmons has a bunch of mass balance equations for calculating optimal flows but for our purposes, a simple airlift siphon provides all the flow needed.

In aquaculture tanks often a center bottom drain is used to eject the slurry. This is because in round tanks the circular hydraulic flows incorporated in round aquaculture tanks by design cause the solids to settle at the center. However, as long as there is a circular flow, an airlift pickup tube will do the job almost as well. It is easy to create a circular flow in a round tank. It can be done with air or water simply by ejecting the medium through an oriented orifice.

It’s only a little harder in a rectangular tank. Placing injector pipes in the corners and orienting the orifices in the same direction does it.

Now here is where it gets controversial. Believe me, I am not trying to pick a fight with scrubbers since I am one too although I disagree completely with the notion that a scrubber should be used to remove NH3 and NO2−. I believe what algae does best is remove NO3− (and phosphate, if that is a problem.) Here’s why.

Ammonia, NH3, is oxidized by nitrosomonas bacteria, not by algae. There are at least a dozen different species but what they all have in common is that they are photophobic. That means they avoid light. In the presence of light they form an opaque slime as a shield. That may be what scrubbers are seeing when they start up a new scrubber filter, that yellow or brown slime that is not algae but some judge to be algae.

Nitrosomonas bacteria metabolize NH3 to NO2− where the nitrobacter bacteria take over. I have not seen any reports that nitrobacter bacteria are photophobic. Now I do not dispute that algae scrubbers can perform nitrification but what I think happens is that colonies of both types of bacteria build on the substrate and green algae only grows after significant amounts of NO3− accumulate. This is the bane of RAS aquaculturists who desire to reuse as much water as possible. Throwing away expensive synthetic seawater in order to get rid of NO3− is both expensive and ecologically unsound. For this reason, and that nitrosomonas bacteria are photophobic, I prefer a separate biofilter upstream from the algae scrubber. That is exactly how I intend to implement mine once my scrubber is built.

There are two chemical pathways for the reduction of NO3−: assimilatory and dissimilatory. Assimilatory is regulated by NH4+ and uses plants, fungi, algae and bacteria. Dissimilatory is regulated by O2 and C/N (carbon/nitrogen ratio) and uses anaerobic and heterotrophic bacteria. The former is what algae scrubbers do; the later is what bioflocs do.

Now think about that for moment. Nitrosomonas and nitrobacter fellows are aerobic while heterothrophs are anaerobic. Imagine trying to manage colonies of all three in the same soup. The concept comes from waste management and the eggheads are trying to apply it to aquaculture. It obviously can be done but getting it wrong outside of an academic research facility could cause one to go bust.

Currently there appears to be no academic interest in the former but lots of effort and research dollars are being spent on the latter. I think this is a mistake and have said so at Cornell and Texas A&M but since mixed-cell raceways are what are being promoted, bioflocs are preferred to algae scrubbers.

There is an interesting graph that shows the typical startup characteristics of bringing a new biofilter up to full capacity. It shows that ammonia concentration peaks at 14 days, nitrite peaks at 28 days and nitrate begins to accumulate after 21 days. This chart may explain the time lags folks implementing scrubbers see when they add one to their system. In short, first you get ammonia, then nitrosomonas critters, then nitrite, then nitrobacters, then nitrate, then green algae, in that order.

https://ag.arizona.edu/azaqua/ista/ISTA7/RecircWorkshop/Workshop%20PP%20%20&%20Misc%20Papers%20Adobe%202006/7%20Biofiltration/Nitrification-Biofiltration/Biofiltration-Nitrification%20Design%20Overview.pdf

See page 8 for the chart.

[amwassil]

Wow! Thanks very much for that detailed explanation. I'm dealing with fresh water, although I think many others on this forum are into salt and reefs.

I am clear on the de/nitrification process. My 80 gallon rectangular fish tank with about 75 gallons of water currently has a Marineland C360 canister, 2 Santa Monica Drop 1.2x scrubbers and a 5-gallon home brewed MBBR, soon to be swapped out for a 10-gallon version. My intention is to retire the C360 as soon as the MBBR can take over completely. It's not quite there yet as the bacterial colonization seems to be taking a long time to get established (it's been online for about 5 months). The algae scrubbers are there to remove nitrates, whatever else they do is of little concern to me. I intend to build a single, larger upflow algae scrubber and put the two drops into other smaller tanks that also need nitrate reduction.

Although the water quality in this large tank is good (except for high nitrate) quite a bit of debris accumulates on the bottom. In addition to a pretty heavy fish load, I also have a couple dozen large Apple snails. I currently clean off the bottom with a water vacuum I've made using an Eheim Classic 150 canister. I use this same device to clean the bottom of my turtle tank as well. I am hoping to eliminate the manual cleaning of the bottom somehow. Santa Monica suggested either to leave it alone and let bacteria consume it or to get some triops and see what they can do. It's not like there's an inch or two so I suspect that bacteria are already converting some of it into liquid that can be processed in the various filters. I've also decided to try the triops but have not yet started breeding them. Once I do get the triops started I'll report my adventures in another thread.

I have a question for you, though. I already have functioning MBBR filters on both my turtle and main fish tanks and I use sponge filters covered with 400 micron nylon bags as pre-filters. Still I notice that some debris gets into the MBBR tanks and settles out to the bottom. It's relatively easy to clean that out simply by removing the Hel-x and syphoning the bottom. Or during a semi-annual overhaul by rinsing it out after taking the whole system offline. What I'm wondering is if I remove the pre-filters do you think that would cause any issues with clogging the Hel-x? I suspect the MBBR water tanks are too small to get a really efficient settling action or install a baffle and that most of the debris sucked in would end up in the Hel-x or just recycled back into the fish/turtle tanks via the outflow. What do you think? Thanks.

[SantaMonica]

algae scrubbers can perform nitrification

A simple correction, you probably did not mean that algae can convert ammonia to nitrate.


Dissimilatory is regulated by O2 and C/N (carbon/nitrogen ratio) and uses anaerobic and heterotrophic bacteria

Are you saying that there are two different types of bacterial action? Because anaerobic would not be regulated by O2, correct?

[perlboy]

SantaMonica: You are quoting me correctly but you are not paraphrasing me correctly. I did not say algae can perform nitrification. They can’t. They can perform denitrification because they can assimilate nitrate. What I said and what I meant is that algae scrubbers can perform nitrification, because in addition to hosting algae, they can host nitrifying bacteria. Otherwise, why would anyone recommend an algae scrubber as the only filter in an aquarium?

amwassil: I think your sponge would filter some solids without the 400-micron sock. The best reticulated foam I can find is rated 20 ppi (pores per inch.) You will have to be the judge of whether yours is this porous or more or less. That’s 0.05”. Converting to SI:

0.05 * 25.4 * 1 x 106 = 1,270,000 microns. That’s porous enough to trap lots of solids assuming there is hydraulic flow within the tank to keep solids in suspension long enough to be captured by the filter. Since you are getting lots of settling, the flow isn’t fast enough. With the sock you would only capture fines in suspension. When you clean the sponge what do you see?

All biofilter media have a souring action when agitated. I think the debris you are seeing in your MBBR may be the result of this scouring action rather than stuff passing through that 400-micron sock. Since you report high nitrate concentration your MBBR may be trying to grow some algae, perhaps not the type one would want but nevertheless, some non-bacterial biofilm, and it is being scoured off and if it is not being returned to your main tank, will settle out when you turn off the air. Rather than remove the pre-filters I’d first put a sock on the outflow of your MBBR, to make sure you aren’t passing any of this detritus back to your tank and then remove the socks from the sponges, and very closely inspect what the sponges are trapping. I’d also consider increasing the hydraulic flow in your tank to get less settling and let the pre-filters do their jobs.

SantaMonica: From Timmons, Recirculating Aquaculture, 2007; re your quote:

9.2 Factors Controlling Denitrification

When considering the various factors known to control denitrification, it is important to realize that reduction of nitrate to nitrogen gas proceeds via various intermediates, among them nitrite, a compound extremely toxic to aquatic animals. In aquaculture systems, it is important to identify not only the factors that inhibit or enhance denitrification, but also those that cause intermediate nitrite accumulation by denitrifiers.

Oxygen. Denitrifiers are essentially aerobic organisms (here he is talking about dissimilatory nitrate reduction) with the capability of nitrate respiration in the absence of oxygen. Therefore, under aerobic conditions, denitrification is not expected to take place. However, in aquaculture systems as well as other water treatment systems, nitrate removal in apparently aerobic environments such as nitrifying filters is not uncommon. The observed nitrate removal under these conditions is due to the heterogeneity of the environment. Accumulation of organic matter in an aerobic environment may lead to anoxic conditions within the organic layer or biofilm and may provide suitable conditions for proliferation and activity of denitrifiers. Furthermore, short anaerobic periods of normally aerobic environments may lead to considerable nitrate losses. This is not surprising when considering the fact that denitrifiers form an intrinsic part of microbial communities developing under aerobic conditions. Low oxygen concentrations in the environment may lead to nitrite accumulation as a result of the differential repression of nitrite reductase synthesis (what he is saying here is that the denitrifying heterotrophs are more efficient than aerobic nitrifiers) and activity as compared to nitrate reductase (Coyne and Tiedje, 1990; Korner and Zumft, 1989).

perlboy again: What I believe he is saying is that anaerobic bacteria are always present in a denitrifying community and they replicate during aerobic conditions, in fact, they out-replicate nitrifiers, but only work their magic when conditions are suitable (during anaerobic periods.) This is one of the reasons bioflocs are so difficult to manage since a large volume of water (the mixed-cell raceway they modeled this behavior in was 16.3 m x 5.44 m) can have both aerobic and anaerobic regions and it is virtually impossible to make one or the other uniform throughout.

I’ll say once more, the academic community is focused on dissimilatory (bacterial) processes rather than assimilatory (algae) processes. I can give you Michael Timmons' email address if you'd like to ask him for clarification.

[perlboy]

It's relatively easy to clean that out simply by removing the Hel-x and syphoning the bottom. Or during a semi-annual overhaul by rinsing it out after taking the whole system offline.

amwassil: Most commercial MBBRs have a bottom drain, not necessarily through the floor of the vessel, usually in the sidewall close to the bottom. Since all MBBRs exfoliate (scour) their media, more or less, the bottom drain conceptually serves exactly the same purpose as the bottom drain in a settling tank/clarifier. To use it, turn off the in flow and the air and let the suspended matter settle. How long? Go have a cup of coffee (Canadians drink tea, right?) and when you return, open the bottom drain's valve and purge 10-20% of the water volume. The media floats so it won't be lost. If a few pieces are lost, they are probably at the end of their useful life anyway. Or, put the media in a net bag, loose enough not to interfere with agitation but fine enough to retain it.

[amwassil]

I think your sponge would filter some solids without the 400-micron sock. The best reticulated foam I can find is rated 20 ppi (pores per inch.)


I'm using Ista Round Large Bio-Foam sponges. I can't find any specs for these things but the pore size looks a lot smaller than 20 ppi. My guess would be min 50 and possibly as much as 75-100 ppi. They filter quite satisfactorily by themselves. I added the fabric to protect the sponges. Originally, I had an Eheim 2075 canister on the turtle tank. The filter has an internal 'pre-filter'. The turtles dump a lot of sloughed off skin into the water which clogged the pre-filter quickly and thus required cleaning on a bi-weekly basis. Too much work! So I added bare sponges to the intake screens in both the turtle and fish tanks to keep the skin out of the turtle canister and to enable fewer filter cleanings with the Marineland C360 on the fish tank. Sponges worked great and less trouble to clean than opening the canisters. However, I found that getting turtle skin off and out of the sponge required a toothbrush and elbow grease. Even the sponge in the fish tank absorbed a heck of a load of debris. Thus, the sponges didn't last very long. That prompted me to add the 400 micron bags around the sponges. The bags rinse easily and I can bleach them without killing the bacteria in the sponges. The sponges clean quickly by rinsing/squeezing and now last a lot longer.


Most commercial MBBRs have a bottom drain, not necessarily through the floor of the vessel, usually in the sidewall close to the bottom.

That makes sense for a large container. In my 20-gallon combo filter attached to the turtle tank I've got about 10-12 gallons of water; and in the 5-gallon filter attached to the fish tank about 4-4 1/2 gallons of water. Scooping out the Hel-x to clean the bottom is not much work; plus, it enables me to inspect/juggle the Hel-x to clear any impacted debris. Whenever I stop running the MBBR filters to any reason, I put a nylon sock over the end of the return pipes and leave it there for two or three hours to prevent any debris getting back into the aquaria. If I were to make a bigger sized filter, I would build it around a drainable bottom and I have a couple of ideas of how to do it.

[amwassil]

If I were to make a bigger sized filter, I would build it around a drainable bottom and I have a couple of ideas of how to do it

Actually, I realized after responding with the above, that I can already drain the water out of the container. This because I put unions in the hoses both immediately before and after the water pump to facilitate taking the pump offline for cleaning. The input through the bottom of the container has a three inch ABS nipple screwed into the top of the bulkhead. After removing the pump, I would only need to unscrew the nipple and open the valve to drain the water out of the container. If there was a lot of debris sitting on the bottom I could stir that up to make sure it went out with the water. I hadn't thought about doing that previously. Amazing!

I also just realized that in your previous post "Purging an MBBR" you were likely referring to doing just this: "Go have a cup of coffee (Canadians drink tea, right?) and when you return, open the bottom drain's valve and purge 10-20% of the water volume." So maybe it just took a while for my aging mind to 'get it'. Thanks. And, yes, some Canadians drink tea, the rest of us drink beer. :rolleyes:

[perlboy]

amwassil: Good idea, making maintenance drain relatively easy and using gravity whenever possible.

You and I seem to be on the same page wrt our interest in MBBRs, so I’d like to get your take on another idea I’m pursuing. It’s a DIY Packed Bead Filter. Most PBFs are tasked to remove solids but they also can perform nitrification. There are lots of commercial examples (used in swimming pools, spas and Koi ponds) but they are all hideously expensive, as in: http://www.beadfilters.com/bead-filters/propeller-bead-filters/assembly/

and

http://www.aquadyne-filters.com/Aquadyne-Filtration-Systems-c-2.html

BTW: that first link also contains design sketches for simple-to-build MBBRs.

The propeller washed variety is particularly interesting because by not using air to rinse the beads, it allows the vessel to remain anoxic. Why would one desire an anoxic MBBR? Here is a link to a study that explains the notion known as partial nitrification-denitrification: http://www.bioline.org.br/pdf?se10041

The point of this configuration is the complete elimination of all nitrogen compounds, not just ammonia. It exploits the different rates of growth of aerobic and heterotrophic bacteria by using a 3:1 internal recirculation design, from anoxic to aerobic and back.

One reason the cost of a propeller driven PBF is so dear is the mixer motor, shaft and thrust bearings. The idea I have to agitate the beads during the rinse cycle is to use one or more Koralia directional water pumps – very cheap and clearly, very effective moving water. Another high-cost piece of equipment is the multi-port valves used to control the different flows through the PBF. The same can be accomplished with ball valves and the intake and uptake screens can be made from 0.04 in slotted PVC well screen; all through-tank connections via Uniseals. I’m thinking of making a prototype from a 7-gal bucket with a Gamma-seal cover: http://www.usplastic.com/catalog/item.aspx?sku=1862

Thoughts?

My favorite Vancouver Island Brewery offering is Sea Dog Amber Ale.

[amwassil]

A single filtration unit that transforms toxic nitrogen compounds to oxygen and nitrogen is attractive, which is exactly why I added the algae scrubber to my MBBR. Technically, the PBF filter sounds like an interesting project. Can you make one that does not require water under pressure? Also, I'm leery of anaerobic/anoxic environments, especially in a sealed container.

[perlboy]

Although most PBFs, either propeller washed or blower washed, use pressurized vessels, I’ve found one sand based design that originated at LSU that uses an unpressurized open-top vessel. I will follow up with the company (Dolphin Fiberglass Products, aquaculturetanks.com.) I don’t see why a PBF must be pressurized. It seems to me the only difference between PBFs and MBBRs is one has a static bed while the other is fluidized. They both flow bottom to top. The beads, typically 3-5 mm plastic spheres aren’t technically different other than size and shape from other bio-media. By this I mean they facilitate bacterial colonization. Certainly a spherical shape packs more closely than does the complex cylinders we see in bio-media. It is that packed bed that filters solids, the primary reason PBFs are used in aquaculture.

I was attracted to algae scrubbers for the same reason, I think, you were; removing nitrate compounds that are left behind by MBBRs. But I can’t ignore the advice I’m getting from my friend at Cornell, Michael Timmons. I now have a detailed design of a mixed cell raceway, and surprise, surprise, it employs both an aerobic MBBR and an anoxic PBF. What’s even more interesting, the flow rates through the two filters are different and the output of the PBF is not sent to the MBBR. The MCR design he sent me incorporates what is known as a Cornell dual-drain system. In this design 15-20% of the flow is removed from the tank’s bottom center drain while 80-85% is removed from the tank’s side drain. Picture a side drain as a screened orifice at water level. Typically, it is a side sump with a bottom drain. In the MCR (rectangular, length 3x width) Timmons sent me there are three counter-rotating cells each with a center drain and a side sump. (Could be length 2x width, 4x, 5x, 6x, etc.) The center drain flows, which contain the bulk of the solids are sent to the anoxic PBF. The output of the PBF is passed through an oxygenation cone and then returned to the culture tank. Why? Because a propeller-driven PBF is anoxic, by design.

The side drain flows, which contain both fine suspended waste and waste in solution are sent to the MBBR. Each filter has it’s own pump. The flows are typically 2:1 or 3:1 MBBR:PBF, which is strikingly similar to the 3:1 internal recirculation in that partial nitrification-denitrification study I included. Water is fungible and nitrogen ions at various stages of the nitrification process are very likely well mixed, especially if the tank volume is turned over the recommended 2x/hour.

I was thinking I would build a non-pressurized PBF and an MBBR (small, pilot system to study nitrification) and connect them in series with 3:1 internal recirculation, but now that I’ve seen Timmons’ MCR design, I’ll connect them in parallel with separate flow rates. I’m not sure how much of any of this applies to maintaining reef tanks or a few marine fish but the issue for me is the efficient elimination of nitrates. An algae scrubber is not the only way to do that.

[amwassil]

Well, I admit I'm a 'gear junkie'. Some diagrams or photos would help me visualize more clearly. :rolleyes:

Not saying the PBF would be usable for my needs, which are pretty simple. You're dealing with commercial scale requirements. None-the-less I'm still interested. Thanks.

[perlboy]

Well, I admit I'm a 'gear junkie'. Some diagrams or photos would help me visualize more clearly. :rolleyes:

Rats! I reduced the .pdf Timmons' design doco to one page which shows a plan-view of a mixed-cell raceway. Unfortunately, it is 150.0 kb. Forum limits .pdf type to 19.5 kb. If I had your email address I'd send it and we can discuss offline. If you'd like to contact me offline, please visit thomasdocheri.com and use my contact page to make a non-public connection.

[amwassil]

I have no objections to discussing privately via email. However, I think there are probably others on this forum who are interested even if not commenting so I'd prefer to keep the discussion here. That said:

You could try displaying the relevant portion of the .pdf onscreen, blow up the diagram and make a 'screen copy' of the diagram. Upload that .jpg to the forum. For example, from http://www.bioline.org.br/pdf?se10041:

6245

I originally advised uploading as either .jpg or .png, but .png does not work correctly. So I retracted that.

[perlboy]

6261

As requested and with image editing assistance by amwassil. This one is much larger than the pilot I intend to build. The key dimensions are length 3x width for a 3-cell raceway. There is nothing magic about three cells; could be, two, three, four, or whatever space permits.

Here is the text by the design's author that sets the context for the plan-view:

Design Summary: Growout System

Figure 6 shows the basic layout for the mixed-cell raceway production system. The basic design concept of the mixed-cell raceway is to operate it as a series of adjacent counter rotating square/octagonal tanks, each having a center drain for continuous removal of solids and sludge. A series of vertical pipe sections with jet ports are installed in the corners of each cell and water directed tangentially to create rotary circulation. Water is then withdrawn from centrally located floor drains. The double drain system takes advantage of the flow pattern in the mixed-cell raceway cells, which forces solids to the center drains for quick removal to the solids capture system. The sidewall drain has minimal suspended solids loading and is pumped directly to the Moving Bed BioReactor (MBBR), which removes ammonia-nitrogen by converting it into nitrite-nitrogen and then to nitrate-nitrogen via bacteria attached to the floating media. Although there is normally a significant amount of passive nitrification (10 to 25% of the total) in the tanks due to bacterial growth on walls, inside pipes and elsewhere, this has not been included and can be considered a safety factor. In addition, the MBBR is designed with only a fill ratio of 50%, i.e., 50% of the volume as media, which can be increased to 65% if additional nitrification is needed.

[SantaMonica]

File size should not be a problem:

size width height

bmp 20000 620 280
doc 20000
gif 20000 620 280
jpe 20000 620 280
jpeg 20000 620 280
jpg 100000 None None
pdf 20000
png 20000 620 280
psd 20000 None None
txt 20000
zip 100000

[amwassil]

Please post the source link here. The file limits as posted by SM look sufficient. Maybe the resolution is more than 72 dpi? Thanks.

[amwassil]

Out of academic curiosity, I just googled "algae eats ammonia" to see if anything turned up. Sure enough! From an admittedly cursory survey (several articles) it appears that algae (and other aquatic plants) can, indeed, consume ammonia/ammonium. In fact, ammonia/ammonium is something like 50 TIMES more bio-available than nitrate and about 20 times more bio-available than nitrite. Consequently, algae will preferentially consume: first, any available ammonia/ammonium; second, any available nitrite; and, third, any available nitrate. So it seems quite correct, as SM claims, that an algae scrubber can be the sole filtration system with no help from bacteria.

If in addition you have a filtration system with nitrifying bacteria taking out both ammonia/ammonium and nitrite and spitting out nitrates, the algae will be forced to consume the nitrates.

Any observations/comments about this??

[perlboy]

I don’t know enough about algae metabolism to comment on the rate of nitrification and/or denitrification performed by algae not in the presence of bacteria. There is mention in the aquaculture literature of what is called Assimilatory Nitrate Reduction, which is performed by plants, fungi, algae and bacteria. Unfortunately, the only applications reported thus far are pond culture of shrimp in Israel. No researcher has used ANR in RAS. All of the research I’ve seen or heard about uses Dissimilatory Nitrate Reduction, which depends on bacteria. That’s what takes place in MBBRs and blower-washed PBFs. Propeller-washed PBFs are anoxic and therefore perform both nitrification and to a lesser degree, denitrification, and the proponents of that type of PBF do not promote them for denitrification. Removal of nitrates seems to be incidental in that design and thus far, a market for a nitrate-removing PBF has not emerged. I believe it will.

Therefore, I can’t design an algae based filtration system meant to manage the nitrogen compounds present when the biomass is 60 kg/m3. That is equivalent to 0.5 lbs/gal. That is a reasonable goal for someone producing food-fish for human consumption. You can make a decent profit at that level of productivity. Has any user of an algae scrubber implemented a scrubber that large? If so, what is the formula? Some coral or a few marine fish do not begin to produce the nitrogen compounds that 60 kg/m3 of biomass produce. Filters such as MBBRs and PBFs that host nitrifying bacteria are well understood and well documented in the professional aquaculture literature. I can easily calculate exactly the MBBR needed for a given volume of seawater to manage all but nitrates. Nitrate management has not been studied to the same degree primarily because prior to the culture of tilapia most RAS focused on cold-water species that are nitrate-tolerant. Most RAS operators managed long-term nitrate accumulations by dilution. They dumped the nitrate-rich water into the environment and let others (such as municipal wastewater facilities) deal with the consequences.

Dumping nitrates is no longer tolerated in many communities. Indeed, producing food-fish for human consumption is most profitable if it is located close to urban markets, the very environments most hostile to nitrate pollution. When fish farmers began raising tilapia a new model emerged, pioneered and perfected at the Univ of the Virgin Islands at St. Croix. The UVI model combines tilapia RAS culture and floating bed hydroponic lettuce production. The nitrate rich water from the tilapia tanks is pumped to shallow raceways, typically 12” deep on which 4’ x 8’ x 1.5” sheets of styrofoam float and support non-fruiting vegetables, such as lettuce and basil. The lettuce plants take up the nitrate ions and water clean enough for tilapia is returned to the culture tanks. It’s a little more complicated than this because the pH needs to be adjusted both coming and going but essentially, fish waste fertilizes lettuce symbiotically.

This is cool if you wish to raise tilapia and lettuce but works not at all if you wish to raise marine shrimp in seawater at 35 ppt. Shrimp are an order of magnitude more profitable and several orders of magnitude more popular than tilapia. Additionally, if you cut tilapia, in other words, if your product is tilapia fillets, then the cost of setting up an FDA/HACPP certified processing plant is almost 2x the cost of the RAS. Unless you’ve got megabucks like Tyson or unless your facility is in China, tilapia isn’t a very profitable business, at least not for the small operator.

Enter Pacific white shrimp. There is a solid market for fresh whole shrimp, with the heads on. Thus, there is no post-harvest processing. You can do that if you wish but why go to that trouble if there is a ready market for whole shrimp. Restaurants remove the heads and shells and make marvelous seafood stock from them. Some folks prefer shrimp rather than clam chowder. Simply replace the clam meat with shrimp and the clam juice with shrimp stock. Thus no HACPP plan is required that must be approved by the FDA.

My problem is how to design a filter that can remove nitrates from expensive synthetic seawater, say in a 2,000 gal tank, that cannot be discharged into the environment and that supports a biomass of 60 kg/m3. I came to algaescrubber.net looking for the engineering data. Most of what I’ve seen so far is small-scale, anecdotal and a great many failures are reported. I’m still looking but a mix of anoxic and aerobic biological filters seems more promising. The data is readily available for each type separately. The challenge seems to be getting the mix, the size and the flow rates in balance so both AOB and NOB bacteria can coexist. For that I can build a small pilot system for a modest investment and test its ability to manage all nitrogen compounds. If I can’t make it work, well than I haven’t spent the kids inheritance, plus I have attracted the interest of several academic colleagues who are interested in what I intend to do. It appears that managing shrimp in RAS rather than ponds is an idea whose time has come. But I’m open minded. Show me a successful algae scrubber that can do the job I need done and I’ll gladly be its biggest fan.

[SantaMonica]

Put the feed into little frozen fish cube trays and measure your daily feeding, and then use the cube-feeding guideline to tell you how big the scrubber should be.

[perlboy]

I asked for an example of a commercial scale algae scrubber and you respond with reef tank nonsense? Cubes? Get real. 60 kg/m3 biomass in a 2,000 gal tank converted to SI units is 7,571 L / 103 x 60 kg = 454 kg. We don't feed cubes. At 3% by weight that's 13.6 kg of 32% protein Zeigler Bros commercial shrimp food per day, fed continuously 24/7 from at least 3 spring powered belt feeders, each holding 10 lbs of pelleted feed. Come on SantaMonica, you may have found a solution for hobbyist reef tanks but you are out of your depth discussing commercial scale aquaculture. Anyone reading this doing what I'm trying to do with an algae scrubber, please respond with dimensions, media, size of pump, pump flow rates, algae species cultivated, ratio of algae in kilograms to the volume in liters of the vessel or vessels that contain it, in short, the engineering specifications of such a device?

[perlboy]

If in addition you have a filtration system with nitrifying bacteria taking out both ammonia/ammonium and nitrite and spitting out nitrates, the algae will be forced to consume the nitrates.

Any observations/comments about this??

This is an interesting observation and deserves a response. Let’s pretend there are no algae present, only bacteria. You are correct, there is a conflict going on between the aerobic bacteria (those that consume ammonia and nitrites and produce nitrates) and the heterotrophic bacteria (that consume nitrates and produce water and nitrogen gas. From Recirculating Aquaculture, Timmons & Eberling, 2007, the chemical equations for nitrification and denitrification by bacteria are as follows:

1) nitrification
NH4+ + 1.83 O2 + 1.97 HCO3- → 0.0244 C5H7O2N + 0.976 NO3- + 2.90 H2O + 1.86 CO2


2) denitrification
0.2 NO3- + 1.2 H+ + e- → 0.1 N2 + 0.6 H2O



These formulas show the following reactants:

HCO3- demonstrates that nitrification removes alkalinity and will cause pH to fall over time;

C5H7O2N is the chemical equation for the bacteria biomass;

e- represents a source of carbon, typically fish feces, but a supplement such as methanol may be required.

It is worth noting that bioflocs (ZEAH systems) contain both types of bacteria, in the soup the shrimp live in. Algae are also present but are not managed in any engineering sense of that word.

Unfortunately, what equation 2) does not show is the intermediate product NH4+, ionized ammonia. This is precisely what equation 1) is trying to remove. So, clearly, the two processes are fighting each other, and since heterotrophic bacteria out-reproduce aerobic bacteria, the heterotrophs will win unless properly managed – preferably, in separate vessels.

Managing these populations so they are in balance is the point of using non-algae filtration methods to perform both of these processes. There are two differential equations (TBD) that define the physical manifestation of at least two filters, one aerobic, the other anoxic. That paper I posted that reports a partial nitrification-denitrification study in Iran successfully solved the problem using glucose as a carbon source in a small laboratory experiment. The challenge, at least for me, is to scale this model up to commercial size, or find someone, such as James Eberling at AST who can.

Now if anyone can design an algae scrubber of commercial scale that can perform both tasks simultaneously, you could go into business manufacturing them, make a fortune selling them to tilapia producers and compete with AST. Their PBF-25 Propeller Washed Bead Filter shown in the mixed-cell raceway plan-view I uploaded sells for a cool $12,578. Tilapia producers nothing; every city in the world with a wastewater treatment facility would be interested in such a filter. That plan, BTW, is for tilapia but is quite suitable for Pacific white shrimp, assuming nitrate can be managed, since nitrates in that plan are consumed by hydroponic lettuce.

Now amwassil, are you saying that you have discovered a species of algae that can directly metabolize ammonia, without any intermediate products? Please post links to papers? Even Dr. Adey in Dynamic Aquaria never made that assertion.

[amwassil]

I'll try to find some citations. The stuff I looked at yesterday had none, unfortunately.

Just a thought. How about a separate 'settling pond' or tank growing algae on the outflow of nitrate-rich water from the bacterial filtration (of whatever type)? It would be along the lines of a hydroponic system with a lot of lights, etc. I guess the issue would be how long the water must stay in the algae tank to reduce nitrate levels to whatever are usable in the stock tanks and whether the algae could grow fast enough for it to be practical. Possibly the water could use gravity flow through a series of such algae tanks each at a lower level to extend the dwell time; might use bubblers and screens to provide substrates for the algae to grow on in the water column rather than just on the surface of the water. You'd get a heck of a harvest of algae out of that, I'd wager.

Which reminds me that I buy algae pellets and wafers to feed my fish. So I wonder what process is used to grow the algae by those manufacturers. I rather doubt they simply send someone out to the local swimming hole to harvest algae around the banks. So there must be some commercial scale process to grow algae out there that might prove useful in your situation. I'll see what I can find for you.

I've discovered via this forum that the terribly misunderstood algae plant is really a remarkable member of the aquarium, but whether its filtration capabilities are practical for a commercial scale operation such as yours remains to be seen. If it took a two acre algae pond to filter out the nitrates from a 2000 gallon stock tank, it would not be a feasible option.

I think SM was suggesting you measure your feeding in 'cubes' for your test tank. You already know how much you're feeding in your commercial tanks. What would that be in cubes? 10,000 per day or there abouts? Math is not my forte :rolleyes:

[amwassil]

Here's an idea from another thread in this category:

http://algaescrubber.net/forums/showthread.php?3409-Please-check-my-math-and-logic-for-a-first-scrubber-build&p=38368&viewfull=1#post38368

This is a very simple design for a scrubber that could be scaled up. I could see having multiple small screens hanging from a single water pipe, or with sufficient flow/pressure a single long screen extending the full length of the stock tank. Or multiple, sideways 'stacked' screens on two or three pipes over the center of the tank (lighting challenge here). Something like this could draw water out of a single or multiple screened inputs at the end of the stock tank, rather than standing in the water as this small one does. Also, if positioned high enough, the screens could drain into a trough with a downspout at one or both ends rather than directly back into the tank. Then there would be no interference with tank cleaning/maintenance. Also, don't necessarily have to use straight pipe.

It seems to me that this design would lend itself to a small scale test of efficiency for removing nitrate which could then be directly scaled up. If something like this worked, it could be implemented without additional water tanks.

PS: I can see this working with an air pump, but it would require building the algae scrubber(s) underneath or adjacent to the stock tank. Depending on how the stock tank is supported, I guess it would be more feasible to build the algae scrubber(s) adjacent to the tank. The tank is round, yes? That would complicate construction of the algae scrubber(s); or, if there was adequate clearance the scrubber(s) could be straight I guess.

[perlboy]

I think SM was suggesting you measure your feeding in 'cubes' for your test tank. You already know how much you're feeding in your commercial tanks. What would that be in cubes? 10,000 per day or there abouts? Math is not my forte :rolleyes:

There's a lot going on in this post so I'll try to respond, one issue at a time.

The quantity fed/day is the most critical issue wrt biofiltration; TAN/day (total ammonia-nitrogen, kg), so I'll tackle that one first. I'm good at math so I'll do the calcs and show how the standard fish/shrimp respiration assumptions are used to calc TAN in aquaculture. But first we need to agree on the definition of a cube. What does one weigh in grams and what is its protein content? Or, if cubes can be ordered with varying amounts of protein, what are some typical values? I'll review the latest FAQ for the definition of media. I'll use that definition to create a cube equivalent and a hypothetical filter for different sizes of culture tanks. Remember, the max bioloading is 60 kg/m3 regardless what size tank is being used. Is that a fair test of how an algae scrubber must be scaled? I won't attempt to design one at those levels but it should serve to ask the question of whether a practical scrubber with the required performance is feasible.

[amwassil]

There's a lot going on in this post so I'll try to respond, one issue at a time.

Sorry. I'm an 'idea guy'. Something occurs to me and that leads to something else and I just spit them all out and let you organizational guys deal with it. :confused:

I found a cited article that itself contains a multitude of citations regarding use of algae to remove inorganic nitrogen compounds and other non-desirables from waste water.

http://www.sciencedirect.com/science/article/pii/S1319562X12000332


Abstract

Organic and inorganic substances which were released into the environment as a result of domestic, agricultural and industrial water activities lead to organic and inorganic pollution. The normal primary and secondary treatment processes of these wastewaters have been introduced in a growing number of places, in order to eliminate the easily settled materials and to oxidize the organic material present in wastewater. The final result is a clear, apparently clean effluent which is discharged into natural water bodies. This secondary effluent is, however, loaded with inorganic nitrogen and phosphorus and causes eutrophication and more long-term problems because of refractory organics and heavy metals that are discharged. Microalgae culture offers an interesting step for wastewater treatments, because they provide a tertiary biotreatment coupled with the production of potentially valuable biomass, which can be used for several purposes. Microalgae cultures offer an elegant solution to tertiary and quandary treatments due to the ability of microalgae to use inorganic nitrogen and phosphorus for their growth. And also, for their capacity to remove heavy metals, as well as some toxic organic compounds, therefore, it does not lead to secondary pollution. In the current review we will highlight on the role of micro-algae in the treatment of wastewater.

Not sure if these guys ever get around to claiming algae eats ammonia/ammonium, but for us, here are some interesting excerpts:


Since the land-space requirements of microalgal wastewater treatment systems are substantial (De Pauw and Van Vaerenbergh, 1983), efforts are being made to develop wastewater treatment systems based on the use of hyperconcentrated algal cultures. This proved to be highly efficient in removing N and P within very short periods of times, e.g. less than 1 h (Lavoie and De la Noüe, 1985).


The algal systems can treat human sewage (Shelef et al., 1980, Mohamed, 1994 and Ibraheem, 1998), livestock wastes (Lincoln and Hill, 1980), agro-industrial wastes (Zaid-Iso, 1990, Ma et al., 1990, Phang, 1990 and Phang, 1991) and industrial wastes (Kaplan et al., 1988). Also, microalgal systems for the treatment of other wastes such as piggery effluent (De Pauw et al., 1980, Martin et al., 1985a and Martin et al., 1985b and Pouliot et al., 1986), the effluent from food processing factories (Rodrigues and Oliveira, 1987) and other agricultural wastes (Phang and Ong,1988) have been studied. Also, algae based system for the removal of toxic minerals such as lead, cadmium, mercury, scandium, tin, arsenic and bromine are also being developed (Soeder et al., 1978, Kaplan et al., 1988, Gerhardt et al., 1991, Hammouda et al., 1995 and Cai-XiaoHua et al., 1995).


The technology and biotechnology of microalgal mass culture have been much discussed (Burlew, 1953, Barclay and Mc-Intosh, 1986, Richmond, 1986, Lembi and Waaland, 1988 and Stadler et al., 1988 and Cresswell et al., 1989). Algal systems have traditionally been employed as a tertiary process (Lavoie and De la Noüe, 1985, Martin et al., 1985a and Oswald, 1988b). They have been proposed as a potential secondary treatment system (Tam and Wong, 1989).


A complete tertiary process aimed at removing ammonia, nitrate and phosphate will thus be about four times more expensive than primary treatment. Microalgal cultures offer an elegant solution to tertiary and quinary treatments due to the ability of microalgae to use inorganic nitrogen and phosphorus for their growth (Richmond, 1986, Oswald, 1988b, Oswald, 1988c, Garbisu et al., 1991, Garbisu et al., 1993 and Tam and Wong, 1995). And also, their capacity to remove heavy metals (Rai et al., 1981), as well as some toxic organic compounds (Redalje et al., 1989), therefore, does not lead to secondary pollution. Amongst beneficial characteristics they produce oxygen, have a disinfecting effect due to increase in pH during photosynthesis (Mara and Pearson, 1986 and De la Noüe and De Pauw, 1988).


14. Conclusion
Algae can be used in wastewater treatment for a range of purposes, including;
1. reduction of BOD (biochemical oxygen demand, for those of us who didn't know),
2. removal of N and/or P,
3. inhibition of coliforms,
4. removal of heavy metals

Here's a photo from the article of an algae scrubber with attitude (or on steroids)! Technically, a tubular photobioreactor:

6262

This entire article is very interesting, though it covers more than we are particularly interested in. The bibliography contains 50 literature references from A-D only! I didn't take the time to count them all.

[amwassil]

I think all will find this of particular interest. These guys figured out how to boost the performance/efficiency of algae to remove nitrogen:

http://www.sciencedirect.com/science/article/pii/0043135485903112


Abstract

Algal cultures of Scenedesmus obliquus at low concentrations (0.1–0.2 g dry wt l−1) provide adequate biological tertiary treatment of wastewaters. This research was aimed at studying the possibility of increasing the system performance by using hyperconcentrated cultures of S. obliquus (up to 2.6 g dry wt l−1) at the laboratory scale. The algal culture grown on secondary effluent was first chemically flocculated with chitosan (30 mg l−1) and decanted; the sedimented culture (5 g dry wt l−1) was then resuspended in secondary effluent to obtain algal suspensions at various concentrations, the performance of which was compared to that of a control culture (0.13 g dry wt l−1). The rate of exhaustion of nitrogen (N-NH4+) was proportional to the algal concentration and a complete removal could be obtained within 15 min (at 2.6 g dry wt algae l−1); this result compares favorably to the 2.5 h or so required by the control culture. The unit uptake rate for nitrogen (N-NH4+) had a tendency to increase with the algal concentration, whereas that of phosphorus (P-PO43−) showed the opposite relationship. Considering the results obtained, it appears that hyperconcentrated algal cultures have a high potential for the tertiary treatment of wastewaters; a significant reduction of pond surface for large scale operations can be anticipated.

My bold. Unfortunately this article is paywalled, so no quotes.