A summer fellow's poster documenting the benefits, and the journey, of creating radial, self-cleaning flow in a rectangular tank.

Aquaculture engineering:

Aquaculture, the rearing of aquatic organisms for food in high densities, requires special systems to control environmental conditions and maintain water quality with the efficient removal of chemical and biological waste.  

Generation 1: From Turtles to Trout

LITTLE FISH IN A BIG POND -  500 fingerling trout in a 10,000 gallon tank made for very spacious accommodations...initially.

LITTLE FISH IN A BIG POND - 500 fingerling trout in a 10,000 gallon tank made for very spacious accommodations...initially.

Our first pilot project tasked us with stocking a 10,000 gallon recirculating system designed for sea turtles with 500 fingerling rainbow trout.  Over several months, the trout were grown out to 500 grams each but our system could not keep up with the solid waste.  The pilot established a proof of concept, but in order to grow larger fish, we needed a more powerful system.

System improvements included replumbing the protein fractionator for increased countercurrent flow, incorporating a diatomaceous earth (DE) filter to polish water, increasing biofilter capacity, and installing a larger capacity UV filter for better sterilization. 

But we still needed to improve solids removal. 

Generation 2: Self Cleaning Tank Design

BIOMASS MONITORING - A subsample of trout were taken weekly to determine their feed conversion rates, which is their efficiency for turning feed calories into body weight.  Biomass estimates were then used to determine feed rates to maximize growth and minimize wasted food.  

BIOMASS MONITORING - A subsample of trout were taken weekly to determine their feed conversion rates, which is their efficiency for turning feed calories into body weight.  Biomass estimates were then used to determine feed rates to maximize growth and minimize wasted food.  

Through the generosity of Pratt & Whitney (the jet engine people!) funding a summer fellowship in aquaculture engineering, and a lot of research, we identified the Cornell dual drain system as an optimal design.  It was capable of isolating and removing 95% of solids by concentrating them with cyclonic force that induced a secondary radial flow to direct solids towards drains and away from mechanical filtration intakes.  

Our concrete rectangular tank was not the optimal shape and did not offer side or bottom access required to retrofit the Cornell system.  Our solution was to reverse engineer as many Cornell system design features as possible to see if we could create rotational flow and induce the desired self cleaning radial flow.  

GENERATION 1 COMPLETE -  As the trout reached 4-5", we started to push the limits of our filtration system which increased the frequency of maintenance and now required 24/7 attention.  The good news was that we proved our concept! 

GENERATION 1 COMPLETE - As the trout reached 4-5", we started to push the limits of our filtration system which increased the frequency of maintenance and now required 24/7 attention.  The good news was that we proved our concept! 

Design features included fabrication of three-way adjustable vertical manifolds outfitted with sight glasses to monitor system balance and create uniform tank flow.   We also modified our central drain to capture and divert solids away from the main filtration pump intake, and installed aeration stones to induce vertical lift.

The newly engineered system produced the signature doughnut-shaped whirlpool depression at the center of the tank.  Data collection on surface currents identified rotational velocities conducive to rearing trout.  Fish feed was thrown into the system to simulate waste.  The shape and concentration of the solids deposited on the tank bottom confirmed radial flow and identified dead spots, helping to inform vertical manifold flow and position adjustments.

Generation 3: Full RAS System

Successful outcomes from the pilot projects gave proof-of-concept and justified significant capital investments in equipment and infrastructure including perimeter walkways and safety rails.  The RAS system included bead filtration, oxygenation, UV sterilization, and protein fractionation just to name a few.  The system's construction was completed in late 2016 with hopes for stocking in early 2017.

The room configuration at the start of Generation 1.

The room configuration at the start of Generation 1.