The Water Quality Multiplier
Charles Tillman has an interesting claim to fame. The Chicago Bears cornerback has forced 39 fumbles in his professional career and an impressive 4 in one game. Since such statistics have been kept, no other player has matched this performance. The basic job of a defensive player is to stop the advance of the opposing offence. Tillman’s focus on forced fumbles (and interceptions) doesn’t just stop the advancing offense, but does something far more effective – takes them right off the field and brings his own offense onto the field. The majority of teams’ “offensive point share percentage” is more than 90% making a forced fumble is at least 10x more effective than a tackle.
If an analogy were made to recirculating aquaculture systems (RAS), winning the game is sustainably and profitably growing fish. Offensive actions are biology related – fish husbandry, feeding, grading, and breeding. Defenses would include the water treatment systems designed to provide the necessary environment for optimal growth.
In this analogy, effective solids removal is the Charles Tillman 10x multiplier. RAS are dependent on effective solids removal. Without it, the biofilter, the CO2 removal devices, the oxygenation, are all likely to be less efficient, less reliable, and deliver less predictable water quality. Less water quality means less ‘offense’ – read system biomass capacity. Less offense means less ‘wins’ – read growth of healthy fish.
The biofilter can become clogged with solids decreasing its surface area. The viability and quantity of nitrifying bacteria are thus diminished. The solids provide supplemental surface area for supporting other bacteria throughout the system. Decreased effectiveness of both ozonation and UV treatment due to the suspended solids in the water, aids the proliferation of unwanted bacteria. The increased bacterial population consumes oxygen, and releases wastes contributing to higher ammonia levels and more. An added risk of mechanical failure is present due to solids plugging filters, or simply the elevated loading on various pieces of equipment.
Commercial intensive RAS may be a relatively young industry. However, if there is one thing we should be doing right by this point, it is solids removal. Suspended solids are possibly the water quality parameter we can observe best without any test equipment other than the human eye. We can watch particles in the water. We can gauge their size and concentration. We can see how buoyant they are and observe how currents affect them. Yet, one 2012 study reported that solids removal was cited by over two-thirds of consultants and researchers, and by 14 of 16 growers as the number one challenge in RAS. Reasons given are varied, with factors from design to management of RAS being pointed at as contributing factors.
In recent years, Scotian Halibut has had the opportunity to compare tanks of fish running on RAS with tanks running on flow through. These were simply informal studies conducted during commercial production.
The first case compared two tanks of on-growing halibut. The two identical tanks contained the same families, same initial size, same initial stocking density, and the same temperature regime. The only difference between the two tanks was flow-through water vs recirc water. Very early on, the fish in the flow-through tank began eating 30% more than the fish in the recirc tank. This continued for the months that the trial was carried out. The end result was that the flow-through tank’s fish grew at a rate 30% higher than their counterparts in the recirc tank.
Reasons for the increased growth were discussed but not exhaustively investigated – CO2, ammonia, pH, water clarity, solids – all were at more beneficial levels in the flow through tank. General consensus (and concurrently published research) indicated CO2 may have a more significant effect than previously considered.
The second case compared the history of a brood stock tank that had been on a recirc system for 12 years with its performance on flow through for a one year period. The CO2 and pH values were maintained at similar values as the RAS had experienced. As with the on-growing fish, there was an immediate increase in feed intake of approximately 30% that was sustained throughout the trial. The quantity of eggs harvested from the tank increased by far more than 30%. Whether this was an annual anomaly or directly attributable to the trial is too early to tell. But the main suspect and major difference in water quality is the lack of fine solids.
In conclusion, effective solids removal is the key defensive player in a recirculating aquaculture system. To get RAS working at its peak efficiency, suspended solids must be dealt with properly. Beware of over-feeding. Choose feed that has a minimal quantity of fines. Apply primary solids treatment at the point in the system where the solids are largest. Then polish with a secondary treatment. The technology exists. The suppliers exist. The engineering expertise exists. The Chicago Bears pay Charles Tillman $3.5 million per year to provide his offense with more time and opportunities to win. If solids in your water are detrimentally affecting your RAS, investing in proper solids removal means buying your fish a bigger appetite, increased health and growth. Multiply your wins.
An Outlook on Solids (PDF)