News
23 october 2018

The importance of intake water

Ensuring success at large-scale recirculating aquaculture facilities

Inland fish farms utilizing recirculating aquaculture systems (RAS) will be key players to help meet the global demand of fish production. The number of inland RAS systems is expected to skyrocket in the near future. According to independent research and advisory firm Lux Research, by the year 2030 more than 40% of the world’s global aquaculture production volume will be grown in advanced RAS systems.
 
There are numerous factors for fish farmers to consider as they develop RAS projects and evaluate potential site locations. An experienced workforce, geographic proximity to key markets, climate, environmental regulations, and of course, available water sources and the ability to discharge water are a few of these considerations. Therefore, it is important to undertake an in-depth analysis of the physical, chemical, and biological characteristics of a potential site’s water source.
 
The importance of intake water quality
Water quality is the most critical element of a RAS system. It helps ensure satisfactory fish health and can even affect the quality of the harvested product. The newest generation of large-scale RAS systems are engineered to be very efficient in recycling and maintaining water quality within the system. Though these systems are considered to be closed-loop and can recirculate more than 99.5% of the water, they still require a large amount of high-quality intake water to continually replenish the system.
It is vital to thoroughly evaluate all water sources in the early stages when developing a new aquaculture project,” says Frédéric Gaumet, Ph.D., Business Development Manager of Aquaculture for Veolia subsidiary Krüger Kaldnes in Norway. “Performing this analysis at the start of the project can help avoid expensive equipment retrofits to properly treat incoming water.
 
Understanding your water source
Though aquaculture has a very low water footprint when compared to other agribusinesses, it still depends heavily on a reliable source of water. Managing water resources efficiently can contribute to the overall success of a facility’s operation. Because of this, water should be a leading factor during the site selection process. Not only is the available volume of water important, but the physical, chemical, and biological characteristics are equally significant. Also critical is biosecurity. Regardless of the water source, there should always be upfront water treatment to ensure the water is disinfected to maintain the biosecurity at the facility. Depending on the water source, additional treatment may be needed to ensure a successful RAS operation.
 
Most likely, water sources at a potential site will be one of these sources: groundwater, surface, seawater, or municipal water. Each water source has its own particular treatment challenges for RAS systems. For instance, surface and seawater may have contaminants and other biohazards that can create biosecurity concerns. It is possible to use sea or surface water as a supply source, but in all cases, the costs to treat this water should be closely evaluated.

If the site location is in a developed area, facilities will likely be able to connect to a municipal water source. Although these sources are relatively consistent in terms of quality and quantity, making them very reliable, they still present treatment challenges. At the minimum, municipal water will need to be treated to remove residual chlorine and potentially trihalomethanes. The largest downside of municipal water as a source for aquaculture is the cost. This water is usually expensive and can negatively affect the economics of the project.
 
Groundwater is usually the preferred source of water for inland aquaculture. Firms do have to ensure that the groundwater source can support the volume of water an aquaculture operation consumes yearround. The water supply should also be able to accommodate future production expansions and tertiary water needs, such as fish processing and hatchery and fingerling/fry additions. According to Gaumet, “Capacity and flexibility are very important. In most cases, a farm uses much more water then calculated only for the RAS.
 
What are some of the key elements to identify related to intake water? Although water characteristics greatly vary depending on fish species and type of system, modern RAS’s are able to maintain a very specific aquatic environment. These systems are able to monitor and adjust temperature, pH, dissolved gases, suspended solids, and ammonia.
When it comes to intake water, some key constituents can negatively impact the RAS’s performance and jeopardize fish health.
 
Ensuring success with intake water
Building a strong partnership with an experienced RAS technology provider that has an in-depth understanding and expertise in water chemistry and treatment will help to ensure the success of an aquaculture facility. Through careful analysis of the water and pairing the technological mix to ensure the RAS performance, companies can prevent significant oversights that result in unexpected operational and capital costs.
 
The stakes are high as inland aquaculture transforms itself to be a staple agribusiness. Bioplans and business plans need to be accurate and executable for emerging companies to succeed. Water is a foundational element within these plans. Understanding how water affects a RAS’s operation and the fish living inside of it can provide a competitive advantage for future aquaculture companies.
 

Important water characteristics to evaluate when analyzing available water sources
 

Aquaculture Wave Weftec
 
Total Dissolved Solids (TDS)
Total dissolved solids (TDS) are inorganic salts within the water supply. These include calcium, magnesium, potassium, sodium, bicarbonates, chlorides, and sulfates. Though many freshwater fish can withstand relatively high levels of TDS (>400 mg/l), aquaculture facilities may face challenges discharging this water to the municipality or the environment. The sites most affected by this issue are those in inland regions that would prefer to discharge to surface waters. Many states have water quality standards that restrict the discharge of TDS to freshwater rivers and streams. Groundwater sources can have higher levels of TDS, depending on the depth of groundwater and the local geology. The cost to treat or responsibly dispose of higher TDS wastewater can significantly add to the CAPEX and OPEX of the farm.
 
Hardness (calcium and magnesium levels)
Depending on the geographic location, both groundwater and municipal water are susceptible to having high hardness levels. In most cases, hardness is not harmful to fish health; however, calcium carbonate can precipitate and create deposits within the various RAS equipment. Over time, these deposits can build up on equipment and prevent the RAS from maintaining a suitable water quality to sustain fish health and maximize production. One area most susceptible to hard water is the RAS’s biofiltration system. For RAS that use a fixed film bioreactor, scaling can significantly restrict flow and prevent proper biological treatment. If a moving bed biofilm reactor (MBBR) is utilized, deposit build-up on the  carriers can weigh down the media and reduce circulation inside the reactor. In all cases, this can result in poor performance of the biological process and result in an increase in ammonia levels, causing unsafe conditions for the fish. Another area susceptible to scaling is the degasser. Depending on the design of the system, scaling of the equipment can increase and result in harmful levels of dissolved gases within the RAS.

In most cases, intake water concentrations for hardness (CaCO3) should be under 200 mg/L. If not, it should be treated prior to entering the RAS. One common method to treat hardness is to utilize a high-rate softener that can efficiently remove scale-forming constituents within the intake water before it enters the RAS. This treatment will significantly reduce the possibility of scaling throughout the system.
 
Sulfate levels
The water’s sulfate (SO4) level is another parameter to analyze in preparation for a RAS project. Sulfate commonly occurs in water sources and usually poses no immediate concern for fish health. However, if intake water is high in sulfates and there is an accumulation of biodegradable material from spent food or fish waste, it can promote the growth of hydrogen sulfide-producing bacteria. Fish are very sensitive to hydrogen sulfide (H2S), and the RAS design should anticipate the potential for this condition to occur. If there are elevated sulfate levels in the incoming water, it is important to ensure that the RAS is designed to minimize hydraulic deadspots and other areas where solids can accumulate.
 
Organic contaminants
Another characteristic that is sometimes overlooked in a water supply is organic contaminants. Agricultural runoff of pesticides and herbicides from nearby farms can infiltrate the groundwater. This is a greater concern if the water tables are shallow. Since the application of these on crops is seasonal, it will be important to monitor the water throughout the year to identify whether this condition exists. If so, the water needs to be treated prior to entering the RAS to avoid fish harm or accumulation of these organics in the muscle tissue of the fish that can result in poor taste and possible odors. Organic contaminants can typically be removed with the help of an activated carbon filtration system.