Fish waste in algae scrubber

[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

[amwassil]

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

http://algaescrubber.net/forums/show...ll=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

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.

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...19562X12000332

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:



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...43135485903112

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.