Well, I admit I'm a 'gear junkie'. Some diagrams or photos would help me visualize more clearly.
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.
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.Originally Posted by amwassil
Well, I admit I'm a 'gear junkie'. Some diagrams or photos would help me visualize more clearly.
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:
I originally advised uploading as either .jpg or .png, but .png does not work correctly. So I retracted that.
Last edited by amwassil; 10-24-2015 at 07:41 PM. Reason: info re .png files
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 Water is then withdrawn from centrally located floor drains.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.
Last edited by perlboy; 10-24-2015 at 10:36 PM. Reason: correct typo
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
Please post the source link here. The file limits as posted by SM look sufficient. Maybe the resolution is more than 72 dpi? Thanks.
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??
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.
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.
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?
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