Improving oxygen transfer in a Recirculating Aquaculture System, to increase production and promote the sustainability of raising tilapia indoors.

Progress report for FNC20-1207

Project Type: Farmer/Rancher
Funds awarded in 2020: $26,990.00
Projected End Date: 01/31/2022
Grant Recipient: Ripple Rock Fish Farms LLC
Region: North Central
State: Ohio
Project Coordinator:
Traci Bell
Ripple Rock Fish Farms LLC
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Project Information

Description of operation:

Ripple Rock Fish Farms LLC began almost 8 years ago, with a 3,000 gallon system, producing about 1,500 lbs of tilapia in our first year. As we have gradually expanded our operations, with many successes and failures along the way, we have learned that success in this business boils down to just a few variables: water, waste and oxygen. Today, with production levels topping 40,000 lbs., we continue to closely monitor water, waste and oxygen. Our ever-present goal is to grow more tilapia in less time.

Summary:

With increased demand for locally grown seafood, small farmers in the North Central Region are improving methods to raise fish indoors using Recirculating Aquaculture Systems (RAS).  However, costs to support fish densities at profitable levels is challenging.

The driving force behind any successful RAS is oxygen.  If oxygen levels can be maintained, then waste is neutralized aerobically, feed levels are maximized, fish densities are increased and higher growth rates are achieved.  The solution seems obvious: increase the oxygen levels in the water.  However, liquid oxygen, used by larger operations, is simply too costly to be implemented on a small farm.

The partners on this project seek to improve oxygen transfer rates using cost-effective methods including:

  • Home Health Oxygen Concentrator
  • Venturi Injector, and
  • Oxygen Saturator

This innovative research will broaden traditional RAS methods.  Typically, low pressure systems appropriately designed for small farms, cannot support aggressive oxygen transfer methods.  It’s no wonder that 90% of small scale fish farms fail in the first 5 years of operation. We seek to assist small farmers; stabilizing their presence in this potentially sustainable industry.  Without a doubt, recirculating aquaculture is ecologically sound and socially responsible. The challenge is to also make it economically viable.

 

Project Objectives:
  1. Document current oxygen demand and determine the required oxygen supply necessary to support increasing fish densities (lbs/gallon) by 25%, 50%, and 75% over current levels.
  2. Design a plan to install a Venturi Injector and Oxygen Saturator into the existing raceway, supported by a Home Health Oxygen Generator.
  3. Measure oxygen levels in the water as fish grow (and biomass increases); monitor and make adjustments, over a 3-6 month period.
  4. Expand research to demonstrate the innovation at two additional fish farms, raising similar species, but operating differing systems.
  5. Document results and educate other small, local aquaculture farmers, and aquaponics producers.

Cooperators

Click linked name(s) to expand
  • Craig and Traci Bell - Producer
  • Curtis Gram - Producer
  • CJ Johnson - Producer

Research

Materials and methods:

RAS systems are constrained by the amount of oxygen in the water.  Oxygen in the bioreactor supports the nitrification process and allows feed levels to be maximized. Traditionally, large producers utilize liquid oxygen to keep up with demand.  When production crosses the line of aeration alone large growers use pure oxygen. However, this solution is cost prohibitive to the small scale farmer.

The farmers will conduct trials using a Home Health Oxygen Generator to address the need for efficient oxygen transfer, affordably and sustainably.  The team will combine their experience to design, test and evaluate the use of a Venturi Injector, and Oxygen Saturator, to transfer oxygen from the generator into the water.

Baseline oxygen saturation levels will be measured prior to installation. Once the design specifics have been determined and parts are ordered, equipment will be installed at Ripple Rock Fish Farms on a 22,000 gallon, grow-out system.  Beginning fish densities will be approximately 0.25 lbs/gallon. Over a period of approx. 4 months, densities will increase to 0.50 lbs/gallon and 0.75 lbs/gallon, thereby pushing oxygen saturation levels to test the sustainability of this method.  

Based on the results, adjustments will be made to the delivery system and trials will begin at the remaining two fish farms, sequentially.  By testing the design on three farms, we intend to prove that the research is not system specific and will benefit a broad range of small fish farms.  A research project of this nature has the potential to benefit small farms in a substantial way. Farmers will be able to feed at higher levels, producing fish in a shorter time, and realizing increased profits and better cash flows that will sustain their aquaculture business. 

Raceway system (11,000 gallons each) used for this research project at Ripple Rock Fish Farms LLC.
Research results and discussion:

The focus of this grant is on oxygen.  Specifically, we sought to address how can we more fully saturate the water with oxygen, rather than seeing the oxygen bubble up to the top of the tank, and escape into the air?

ATTEMPT #1 

The first attempt involved 2 steps:

  1. Build a “W” shaped PVC pipe extension (see photo below)
  2. Attach the “W” extension to the header pipe, just past the point of oxygen inflow.
“W” shape extension

The desired outcome was to saturate the water with oxygen as it entered the raceway.  With a “W” shaped pipe flow, retention time was increased, which, in theory, should have super-saturated the water.  However, this didn’t work.   

Results –  Outcomes were measured by the oxygen readings in mg/L as follows:

Average O2 levels (Jan – April):  3.15 mg/L

Average O2 levels (May – June): 3.08 mg/L

The “W” shaped pipe extension failed to mix the oxygen and water effectively.  Oxygen levels remained relatively constant before and after the project attempt.  In addition, the “W” shape collected solids and became clogged, reducing flow, creating additional problems.

ATTEMPT #2

Steps involved in the second attempt were as follows:

  1. Install a venturi.
  2. Build an oxygen saturator.
  3. Replace “W” pipe configuration with oxygen saturator.

An oxygen saturator was connected to the header pipe and replaced the former “W” configuration (see photos below).

Venturi
Saturator
Venturi and saturator

This system operates as follows:

  • Water flows from the pump at approximately 180 gallons/min.
  • The flow from the pump is split. Half of the flow goes to the biofilter (90 gallons/min) and the other half goes through the venturi/saturator (90 gallons/min).
  • An oxygen line is connected to the suction of the venturi. The oxygen is regulated with an oxygen flow meter, coming from the home health oxygen machines.
  • As water flows through the venturi, a suction is created, which pulls in the oxygen.
  • Oxygen and water mix in the saturator.
  • The water flows down the saturator, which sheers the bubbles, super-saturating the water with oxygen, before flowing back into the tank.

 

Results:

Average O2 levels (January – April):   3.15 mg/L

Average O2 levels (May-June):   3.08 mg/L

Average O2 levels (July – Oct):   5.45 mg/L

With the installation of the venturi system and the saturator, oxygen levels have increased 73% from baseline data (January – April).

 

Next Steps:

  • Increase densities of fish in tanks and determine levels of sustainability at Ripple Rock Fish Farms.
  • Install venturi/saturators in additional systems at Ripple Rock Fish Farms, Freedom Fish Farms and Stagecoach Fish Farms.
  • Collect data on potential cost savings.
  • Collect data on increased levels of production/profitability.
Participation Summary
3 Farmers participating in research

Educational & Outreach Activities

Participation Summary

Education/outreach description:

As research is still being conducted, outreach has not taken place yet.  Once the venturi system and saturators are installed at each location, we will collect data and create design plans to distribute virtually, as well as post videos on our YouTube channel.  Outcomes will also be shared with the Ohio Aquaculture Association as a presentation and shared with the OSU extension office.  Based on COVID-19, on-farm tours will be discussed at a later date.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.