Recirculation Aquaculture

Why Recirculation Water use Climate Quality Predation Environmental impact Land Disease Exotic species (or control thereof…

Cost of Labor : $7/day Solids Siphon Near Ensenada, Mexico; 2002

Near Ensenada, Mexico; 2002

Near Ensenada, Mexico; 2002

Raise a lot of fish with Little Labor

Definitions Recirculating System: A production system that reconditions water to extend it’s reuse A technique that increases the value of a limited resource An artificial well that never ceases to flow A stable platform forming a reliable base for commercial production

Five Major Processes 1) Circulation 2) Clarification (Solids capture) 3) Biofiltration (BOD reduction/nitrification) 4) Aeration (Oxygen replacement) 5) Degasification (CO2 stripping)

The Five Major Processes in a Recirculating System Five Major Treatment Objectives The Five Major Processes in a Recirculating System Feeding Circulation Aeration Fish Tank Degasification Biofiltration Solids Capture

Return to Tank Double Drain at Center of Tank

Inlet Outlet Sludge outlet From Under-drain

Over-Drain Flow

Captured Solids

Microscreen Cleaning Jets

From Microscreen Micro-Bead Filter

1 mm Styrene Beads

Centrifugal Pumps

Pressure line from Centrifugal Pumps Oxygen Bubbles 02 Flow Meter Pressure Gauge Water Return to Tanks

Degasification Biofiltration Solids Capture Feeding Circulation Aeration Fish Tank Degasification Biofiltration Solids Capture

Impact of Solids on Recirculating Systems Solids Capture Impact of Solids on Recirculating Systems Increased BOD load (organic solids) causes problems with Biofilters Increased system turbidity (fine particles) Gill damage in fish (fine particles) Aside from their direct physical impact, suspended solids generated in culture systems are highly organic. Most of the suspended solids generated in a recirculating system are feces, reflecting the undigested residuals of feed. Additional solids are generated as bacterial colonies (biofloc) grow from dissolved organic materials found in the water. Both feces and biofloc are mostly organic matter and are thus are subject to further breakdown by bacteria. Over two-thirds of the Biochemical Oxygen Demand (BOD) generated is attributed to suspended solids. It is not surprising, therefore, that clarification was the first wastewater treatment component added to extend water re-use and the first to be used to treat effluents. If allowed to remain in a culture system, solids encourage heavy bacterial growths that can clog (biofoul) a wide variety of treatment units. Excessive growths of bacteria can rapidly deplete oxygen in isolated pockets within a system. Heavy organic loads can inhibit critical nitrification processes in biofilters (Bovendeur et al., 1990). These localized, oxygen depleted zones can stimulate the development of a wide variety of anaerobic reactions that produce odor and contribute to off-flavor development. The bacteria will utilize large amounts of oxygen and produce TAN as they breakdown the solids. Additionally, these enriched conditions tend to cause population explosions of less desirable bacteria, leading to disease outbreaks.

Particle Size Distribution (microns) Solids Capture Particle Size Distribution (microns) Settleable 10-4 10-3 10-2 10-1 1 10 100 Dissolved Colloidal Suspended

Tilapia No Fine Solids Capture

SOLIDS REMOVAL PROCESSES AND PARTICLE SIZES Foam Fractionation Granular Filter Microscreen Tube Settler Cartridge Filter Coarse Screens Plain Sedimentation 100 75 30 10 Particle Size, microns

SEDIMENTATION INFLOW OUTFLOW Solids Capture Vh Vs Settling Zone Inlet Zone Outlet Zone Settling basins have been the clarifier of choice for a number of years. A settling basin is designed to provide an area of quiescent water where the solids can settle out into a cone, from which they can then be removed. More advanced configurations, tube settlers, use a media to shorten settling distances, reducing the size of the settling basin. Performing superbly on systems with high water replacement rates, settling provides poor control of fine suspended solids (< 80 microns in diameter), which tend to accumulate as replacement rates are reduced. This problem, coupled with labor issues, has prompted some to search for a more efficient, yet cost-effective approach. (Vs > Overflow Rate to settle) Sludge Zone

Solid Removal Technologies Solids Capture Solid Removal Technologies Effective for selected particle size Differ in headloss…energy $$$ Differ in labor for upkeep Sensitive to organic loading

Floor Plan

“BYPASS” FILTRATION TANKS Pump Liquid O2 Bead Filter Packed Column Fluidized Bed Packed Column Lime Addition

“IN-LINE” FILTRATION TANKS Shrimp Maturation in South America Pump Bead Filter Fluidized Bed Packed Column

Degasification Biofiltration Feeding Circulation Aeration Fish Tank Degasification Biofiltration Solids Capture

Biofiltration Types of Biofilters

Biofiltration

Biofiltration The classification of heterotrophic bacteria encompasses a great number of genera/species which share the common characteristics of extracting their nourishment from the breakdown (decay) of organic matter. Biochemical oxygen demand (BOD) is largely an indirect measure of the biodegradable organic material in water. Heterotrophic bacteria reduce BOD levels, consuming oxygen in the process. About 60 percent of the organic matter consumed is converted to bacterial biomass; whereas, the balance (40 percent) is converted to carbon dioxide, water, or ammonia. Heterotrophic bacteria grow very fast, capable of doubling their population every ten to fifteen minutes. If the BOD in the water being treated is very high (> 20 mg -O2/l), the heterotrophs will quickly dominate the bead bed, overgrowing the slower growing nitrifying bacteria and consuming tremendous amounts of oxygen. The second, yet more important, classification of bacteria is the nitrifying bacteria. These bacteria are specialists, extracting energy for growth from the chemical conversion of ammonia to nitrite and from nitrite to nitrate (Figure 3.6). Nitrate is a stable end product which, although a valuable nutrient for plants, displays little of the toxic impacts of ammonia and nitrite. Composed principally of two genera (Nitrosomonas and Nitrobacter), nitrifying bacteria are very slow growing and sensitive to a wide variety of water quality factors. It is not surprising that most bead filters used for biofiltration are managed to optimize conditions for nitrification.

Biofiltration

0.45 kg/m3 USDA - SBIR/AST, 97

Production Units

Propellor-washed Floating Bead Filters

Broodstock Return Anti-siphon Bypass valve Sludge View Port Pressure Gauge Sludge Intake

ADM Tilapia System

Degasification Biofiltration Gas Exchange Feeding Circulation Aeration Fish Tank Degasification Biofiltration Solids Capture

Different Behavior Oxygen goes in easier than CO2 comes out Oxygen Gas Exchange Different Behavior Oxygen 21% of air Saturation 10 mg/l Poorly soluble Transfer H20 limited Carbon Dioxide 0.035% of air Saturation 0.5 mg/l Highly soluble 50 mg/l + Transfer gas limited Oxygen goes in easier than CO2 comes out

No CO2 Removal Enrichment Devices Gas Exchange No CO2 Removal Enrichment Devices Commonly used for large scale applications Self-generates pressure (150-200 psi) 1 m3 liquid860 m3 gas Dependent on local source of liquid oxygen Not impacted by power failure 15-35cents/kg typical Liquid Oxygen Timmons and Lorsordo (1994) pg. 188

Air stones Paddle wheels Surface Agitators Spray nozzles Gas Exchange Air stones Paddle wheels Surface Agitators Spray nozzles Packed columns Ambient Air –Oxygen Addition and Carbon Dioxide removal are balanced

Ambient Air Options Gas Exchange Carbon dioxide can be stripped from culture waters by the use of large amounts of air in traditional blown air systems usually consisting of a large rotary blower and banks of airstones. The most efficient approach identified so far involves the use of a packed column aerator (Colt and Bouck, 1984). A packed column degasifier consists of a tall column filled with a porous packing media. Water cascades down through the media as air is forced upwards. When operated with a high air to water ratio, the unit effectively strips excess carbon dioxide gas. Unfortunately, early units were subject to biofouling problems.

Circulation Fish Tank Biofiltration Degasification Circulation Feeding Aeration Circulation Fish Tank Biofiltration Degasification Solids Capture

Airlift Pump Circulation Options Circulation Air Low head centrifugal or airlift pumps are the most common choices for recirculation of waters through the water treatment block in a recirculating system. Centrifugal pumps are extremely efficient at water movement, but, they must matched with the treatment components through their pump curve that relates flow deliver (liter per minute) with the expected headloss (meters of water). The best pumps are expensive but realize considerable savings over the long run generally drawing less than half the amperage of less expensive units commonly marketed for pool applications. Most recirculating systems operate well with head delivery pressures below 5 meters. Additional savings in energy can be realized by use of 220 or 440 V units. Airlift pumps consist in their simplest form of a partially submerged piece of pipe fitted with a air injection line near the bottom. When air is injected the density of the air/water mixture drops allowing water to enter from the bottom of the pipe eventually overflowing the above water lip of the pipe. Airlift pumps are capable of delivering large quantities of water, but, usually only at a few inches of lift. The lift is usually limited to about 30 percent of the submerged depth. Serially placed airlift pumps can lift water several feet but they are not particularly efficient. Airlift pumps are generally used only in systems specifically designed for their use. Their principle advantage is their substantial contribution to the reaeration needs of the system. Once their design variables are understood, they are easily constructed from standard PVC piping. Pump

Airlifts Perform Several Functions Circulation Aeration C02 stripping Foam control

Drop Filters : Low Water Loss Floating Bead Bioclarifiers Filter Mode Drop Filters : Low Water Loss Floating Bead Bioclarifiers Air Bleed Builds Charge Settled Backwash Waters returned to system

Drop Filters : Low Water Loss Floating Bead Bioclarifiers Backwash mode Drop Filters : Low Water Loss Floating Bead Bioclarifiers Released Air Washes Beads Internal Sludge Capture

FAS 1012C: Recirculation Aquaculture Quiz Name:_________________ List the five major treatment objectives and explain what they do. Feeding Fish Tank