perlboy
10-08-2015, 09:29 AM
Hello at AlgaeScrubber.net,
I would like to ask a question about the scalability of this technology.
I am and have been for several years involved in several projects to raise food fish in RAS (recirculating aquaculture systems,) first tilapia and now Pacific white shrimp. To make a long story short, the killer problem with both of those cultures is nitrate accumulation. Both tilapia and various varieties of shrimp are raised in many parts of the world in pond cultures where the nitrate problem is dealt with by dilution. This is environmentally unsound and is not sustainable for the long term. In many coastal areas where shrimp are cultured the ocean is suffering from the artificial nitrate load. Increasingly, there is political resistance to such practices. For example, both California and Alaska have permanently banned the construction of pond aquacultures from their coastal environments. And more intensive fishing is not the answer. From satellite images you can see the damage done to coral in the Gulf of Mexico by bottom trawlers, not to mention the collateral damage of the bycatch, the unwanted species caught and killed as a function of taking the targeted species. By value worldwide shrimp production, fishing and farming, is the leading source of seafood for human consumption, a multi-billion dollar industry.
At the University of the Virgin Islands wastewater from tilapia is successfully used to fertilize leaf lettuce, basil and similar non-fruiting plants in a floating raft system. In Israel promising research in zero-exchange, aerobic, heterothropic systems (ZEAH or by its other name, Biofloc) is being done. Unfortunately, neither approach responds well to downscaling. D.O. in biofloc systems is problematic, especially in smaller (relatively) tanks; balancing the simultaneous management of both aerobic and anaerobic bacteria colonies is challenging and not yet well understood. ZEAH also has a marketing problem: try selling shrimp to consumers after you’ve first explained that the water the shrimp have been living in, and thriving in, resembles a septic tank.
None of the people I’m working with have any confidence in using algae as a nitrate filter. My friend at Cornell recently wrote: “If you want a system that makes a profit, I’d avoid anything to do with algae other than what might occur without intention in a bioflock (sic) system.”
That may be because they have so much intellectual capital invested in dilution and ZEAH but I have yet to see a successful implementation of ZEAH in round tanks. At Cornell and Texas A&M the current thinking is something called a mixed-cell raceway, which is claimed to have the best characteristics of circular tanks and linear raceways. Using air circular adjacent counter rotating currents are created within the raceway to cause solids to settle out at center drains, as they do in round tanks. The remaining waste products are managed by the bacteria in the water, a green soup. Unfortunately, the smallest one of these I have seen, a prototype, is 16.3 m x 5.44 m, built inside a greenhouse (sunlight for photosynthesis,) a long way from the four 2,060 g tilapia tanks at UVI (the folks there scaled their system down to four 380 g tanks but to my knowledge, none of that size has been built. And of course, this does not work with salt water.
I am intrigued by what I have seen and read here. I lurked and read many of the threads before amwassil’s post made me want to register and join the discussion. After learning what he has done with an MBBR/scrubber combo, I’ve spent all my time since designing on paper various down flow and up flow examples in an attempt to see how one might scale them. I can solvent weld acrylic and since light boxes are mostly simple right angles, it seems relatively easy to pack a lot of filtering power into a small space. One back-of-the-envelope up flow design I came up with is four banks of 9 Expressions LED light bars mounted vertically 3 in o.c. in a 35 g Roughneck tote (32 in x 20 in x 19.6 in.) That’s 4x say, 12 x 27 in2 of algae substrate and 324 watts, according to Expressions data, not bad if it does the job, except that’s 18 transformers. Is that really practical? Even if I had to scrape the algae daily because it was assimilating so much NO3-, if the culture tank was free of nitrate it would be a big win.
But what could such a design accomplish?
What could a smaller scrubber, say one half that size accomplish?
What if such a system was too small?
I need to get a better handle on scrubber properties and their scalability before I can proceed to build even a small pilot, since the cost is several thousands of dollars. So, here is my question and the assumptions inherent in the system I want to build:
The smallest round tank in which Litopenaeus vannamei, Pacific white shrimp can be raised to market size, profitably, is 210 g (794 l). This is done with 5 tanks stocked serially every 14 days with 10 g individuals and raised to three cohorts (22.7, 30.2 and 45.4 g avg wgt). Twenty-five % are harvested at 22.7 g, another 25% at 30.2 and final harvest when the remainder reach 45.4 g. There is an 8-week lag before the first tank is ready to harvest but after that there are mature shrimp available weekly. Such a system has a theoretical yield of 3,400 lbs of shrimp/year.
Remember, this is a pilot. If it is successful, the next one might be 5x 500 g tanks, or 800 g, or even 2,000 g, all readily available round tanks, using the pilot system to raise shrimp larvae to stocking size. Picture this: suppose you had a spare fifty grand lying around. You could lease an empty warehouse in Chicago and put in 5x tanks to raise shrimp and sell them locally. Do you see how the scalability of the nitrate filter, whatever type it is becomes the pacing item? I’ll name my first grandchild after whoever helps me permanently solve the nitrate problem, that is, if there is a solution.
Now please consider one tank from the POV of sizing an algae scrubber?
210 g (794 l).
Water volume: 0.794 m3
A minimum of 2x tank volume passed through the filters/hour
Biomass at maturity: 56 kg/m3 (based on experience with tilapia, UVI actually got >60)
Daily feed: 3% of body weight at 35% protein; that’s 0.794 x 56 x .03 = 1.3 kg/day at maturity
FCR (feed conversion ratio): 1.5 – 1.8
Salinity: 32 – 35 ppt
pH: 7.8 – 8.2
Water temp: 28 – 30°C
The scrubber’s only job is the removal of nitrate. A settling tank is typically used to remove suspended solids and an MBBR for nitrification.
So, given feeding 1.3 kg of protein rich food/day during late-stage maturation, what size scrubber would be needed? (I’m assuming the answer to this question is the surface area of the substrate. Please correct me if that is wrong?)
Thanks in advance to all who read, consider and comment.
I would like to ask a question about the scalability of this technology.
I am and have been for several years involved in several projects to raise food fish in RAS (recirculating aquaculture systems,) first tilapia and now Pacific white shrimp. To make a long story short, the killer problem with both of those cultures is nitrate accumulation. Both tilapia and various varieties of shrimp are raised in many parts of the world in pond cultures where the nitrate problem is dealt with by dilution. This is environmentally unsound and is not sustainable for the long term. In many coastal areas where shrimp are cultured the ocean is suffering from the artificial nitrate load. Increasingly, there is political resistance to such practices. For example, both California and Alaska have permanently banned the construction of pond aquacultures from their coastal environments. And more intensive fishing is not the answer. From satellite images you can see the damage done to coral in the Gulf of Mexico by bottom trawlers, not to mention the collateral damage of the bycatch, the unwanted species caught and killed as a function of taking the targeted species. By value worldwide shrimp production, fishing and farming, is the leading source of seafood for human consumption, a multi-billion dollar industry.
At the University of the Virgin Islands wastewater from tilapia is successfully used to fertilize leaf lettuce, basil and similar non-fruiting plants in a floating raft system. In Israel promising research in zero-exchange, aerobic, heterothropic systems (ZEAH or by its other name, Biofloc) is being done. Unfortunately, neither approach responds well to downscaling. D.O. in biofloc systems is problematic, especially in smaller (relatively) tanks; balancing the simultaneous management of both aerobic and anaerobic bacteria colonies is challenging and not yet well understood. ZEAH also has a marketing problem: try selling shrimp to consumers after you’ve first explained that the water the shrimp have been living in, and thriving in, resembles a septic tank.
None of the people I’m working with have any confidence in using algae as a nitrate filter. My friend at Cornell recently wrote: “If you want a system that makes a profit, I’d avoid anything to do with algae other than what might occur without intention in a bioflock (sic) system.”
That may be because they have so much intellectual capital invested in dilution and ZEAH but I have yet to see a successful implementation of ZEAH in round tanks. At Cornell and Texas A&M the current thinking is something called a mixed-cell raceway, which is claimed to have the best characteristics of circular tanks and linear raceways. Using air circular adjacent counter rotating currents are created within the raceway to cause solids to settle out at center drains, as they do in round tanks. The remaining waste products are managed by the bacteria in the water, a green soup. Unfortunately, the smallest one of these I have seen, a prototype, is 16.3 m x 5.44 m, built inside a greenhouse (sunlight for photosynthesis,) a long way from the four 2,060 g tilapia tanks at UVI (the folks there scaled their system down to four 380 g tanks but to my knowledge, none of that size has been built. And of course, this does not work with salt water.
I am intrigued by what I have seen and read here. I lurked and read many of the threads before amwassil’s post made me want to register and join the discussion. After learning what he has done with an MBBR/scrubber combo, I’ve spent all my time since designing on paper various down flow and up flow examples in an attempt to see how one might scale them. I can solvent weld acrylic and since light boxes are mostly simple right angles, it seems relatively easy to pack a lot of filtering power into a small space. One back-of-the-envelope up flow design I came up with is four banks of 9 Expressions LED light bars mounted vertically 3 in o.c. in a 35 g Roughneck tote (32 in x 20 in x 19.6 in.) That’s 4x say, 12 x 27 in2 of algae substrate and 324 watts, according to Expressions data, not bad if it does the job, except that’s 18 transformers. Is that really practical? Even if I had to scrape the algae daily because it was assimilating so much NO3-, if the culture tank was free of nitrate it would be a big win.
But what could such a design accomplish?
What could a smaller scrubber, say one half that size accomplish?
What if such a system was too small?
I need to get a better handle on scrubber properties and their scalability before I can proceed to build even a small pilot, since the cost is several thousands of dollars. So, here is my question and the assumptions inherent in the system I want to build:
The smallest round tank in which Litopenaeus vannamei, Pacific white shrimp can be raised to market size, profitably, is 210 g (794 l). This is done with 5 tanks stocked serially every 14 days with 10 g individuals and raised to three cohorts (22.7, 30.2 and 45.4 g avg wgt). Twenty-five % are harvested at 22.7 g, another 25% at 30.2 and final harvest when the remainder reach 45.4 g. There is an 8-week lag before the first tank is ready to harvest but after that there are mature shrimp available weekly. Such a system has a theoretical yield of 3,400 lbs of shrimp/year.
Remember, this is a pilot. If it is successful, the next one might be 5x 500 g tanks, or 800 g, or even 2,000 g, all readily available round tanks, using the pilot system to raise shrimp larvae to stocking size. Picture this: suppose you had a spare fifty grand lying around. You could lease an empty warehouse in Chicago and put in 5x tanks to raise shrimp and sell them locally. Do you see how the scalability of the nitrate filter, whatever type it is becomes the pacing item? I’ll name my first grandchild after whoever helps me permanently solve the nitrate problem, that is, if there is a solution.
Now please consider one tank from the POV of sizing an algae scrubber?
210 g (794 l).
Water volume: 0.794 m3
A minimum of 2x tank volume passed through the filters/hour
Biomass at maturity: 56 kg/m3 (based on experience with tilapia, UVI actually got >60)
Daily feed: 3% of body weight at 35% protein; that’s 0.794 x 56 x .03 = 1.3 kg/day at maturity
FCR (feed conversion ratio): 1.5 – 1.8
Salinity: 32 – 35 ppt
pH: 7.8 – 8.2
Water temp: 28 – 30°C
The scrubber’s only job is the removal of nitrate. A settling tank is typically used to remove suspended solids and an MBBR for nitrification.
So, given feeding 1.3 kg of protein rich food/day during late-stage maturation, what size scrubber would be needed? (I’m assuming the answer to this question is the surface area of the substrate. Please correct me if that is wrong?)
Thanks in advance to all who read, consider and comment.