RAS Management Basics: How to Avoid Trouble and Ensure Success

Recirculating aquaculture systems (RAS) have grown in popularity over the last decade for a number of reasons. In addition to providing optimal water quality for maximizing fish production, they’re also more efficient than traditional flow-through systems and help fish farms conserve water, energy and space.

But make no mistake: there is a learning curve when making the switch to a RAS. Getting a new recirculating system dialed in takes time, patience and some trial-and-error. As a company that specializes not only in RAS planning and design but also testing, commissioning and training, we’ve seen it all before.

Here are some tricks of the trade to help you ensure your system is running at peak performance and producing robust, healthy and great-tasting fish.

Getting Started

Prior to introducing fish into a new system, it’s important the system be given a thorough cleaning so construction debris or dust don’t clog its components. You want to initially start the system with a sterilized and clean surface.

The initial cleaning entails vacuuming or broom cleaning each area of the system to remove physical material from all surfaces. You should then do a thorough inspection of equipment, such as micro-screen nozzles, to make sure there’s no left over debris. From there you should pressure wash all surfaces. Finally you should go over all surfaces with a disinfectant or fill the system and circulate water mixed with disinfectant through it.

It’s also imperative to properly seed the bio filter, a process that can take anywhere from six to eight weeks. Bio filters are living entities themselves and need to be managed that way. What you’re doing is creating and feeding a filter to grow the bacteria that can convert your ammonia down to a nitrate, and that takes time.

Avoiding Common Mistakes

Once you have fish in the system and things are running well, avoid the natural urge to try to get more out of the system. You need to maintain the proper biomass levels and the proper feeding levels. You also need to continue to monitor things – especially water quality. Do daily water testing so that you have that data available if something goes amiss.

And regular maintenance is mandatory, of course. Follow the prescribed maintenance schedule for each piece of equipment to ensure it keeps running properly and delivers long life.

Dealing with Captured Solids

This is a growing concern, especially as RAS systems are growing in scale. Some larger farms out there can produce the same amount of waste annually as a small town.

The primary solids that you find in a system are made up of uneaten feed and fecal matter. It’s vital that they’re transferred out of the tanks and into the filter system as quickly as possible. There are many types of technology used for this, including micro screen drum or disk filters, foam fractionation and fixed bed filters.

What happens to the waste afterward is where it gets tricky.

Gravitational separation is able to turn the waste into to a low solids material that resembles squishy mud. That can be stored on-site and then periodically removed and used as fertilizer. Some farms have even been able to monetize this to create a new revenue stream for their business.

This is pretty straightforward for freshwater systems. But saltwater provides a distinct challenge because of the saline content, which prevents the waste from being used as fertilizer. So the goal here is to increase the solid content of the waste using technologies you’d see in a waste water treatment plant, like belt filters, filter presses and vacuum drums. Those help create a drier end product that can then be put into a landfill.

Other options include setting up a bio digestion system that works like a traditional septic tank. Microbes eat and digest the sludge, creating methane that can be used for on-site power generation.

Needless to say, a lot of this depends on your site, what kind of facility you have and what local and state regulations allow.

Maintaining a System Not in Use

Fish farms have to take their RAS systems offline from time to time, whether it’s for maintenance or other reasons. When you do that you need to make sure everything is thoroughly cleaned, disinfected and scrubbed before pressure washing it. That includes the pipes and drains because dangerous viruses and bacteria can be lurking anywhere.

Taking Care of Pumps

Pumps fail – it’s just a matter of time. So you need to be prepared for a pump failure before it happens. That means having an extra pump on hand as a backup or, better yet, already plumbed into your system. Time is critical in the event of a failure and having another pump ready to go minimizes downtime and helps you avoid a catastrophic fish loss.

To prevent a failure, you need to keep an eye on your pumps. If you notice decreased performance, it may be time for a replacement. What should you look for? Every day you should check for:

• New noises
• Whining
• Excessive vibration
• Leaks
• Excessive heat

Any of these can be a sign your pump has seen better days. In addition, you should get in the habit of checking amperage levels once a month. Pumps today are pretty robust, but regularly monitoring helps you avoid trouble and keep your facility running smoothly.

UV Treatments

Generally speaking, there are two types of UV systems used in aquaculture: low pressure, high output systems and medium pressure systems. While they both have their pros and cons, we generally recommend the low pressure, high output systems because of they offer:

• Higher output of UV energy in the germicidal range
• Lower operating temperatures for less overall heat gain
• Lower costs
• Longer lamp life

In terms of your UV dose rate, it depends on your objective. There really isn’t a one-size-fits-all approach but to combat most viruses and bacteria the general range is 30 to 60 millijoule per centimeter squared. If you’re targeting a specific pathogen you can go as high as 300 millijoule per centimeter squared to get the desired results.

Minimizing Off-Flavor

Even if your system is running flawlessly, you can still fall victim to fish that just don’t taste right. Fish with an earthy, pond-like flavor are caused by a couple of distinct bacteria types. There are a number of steps you can take to combat them, including:

• Quick removal of solids (as outlined above)
• Proper aeration of your bio media
• The addition of ozone into the system
• Minimizing sunlight into your system.

Following these basic steps will help lessen the learning curve with your RAS system and make it easier to avoid problems down the road. For more information, check out our recent webinar at the RAS Virtual Summit to learn more.

Is a modular RAS system right for you? Check out “The 9 Advantages of Modular Recirculating Aquaculture (RAS) Systems” to find out.