The Truth About Land Based RAS and Water Usage
Land Based Recirculating Aquaculture Systems (RAS) and Water Usage. A guide to understanding what land based RAS means for the environment.
By Kenny Leslie
A few weeks ago, an article was published discussing the water requirements of the proposed moving of BC’s aquaculture industry to land based farms.
It stated that there was a requirement of approximately 4.16 billion litres of water to put the current fish farming industry on land.
The article was slated by an activist group as being, unrealistic or incorrect, or plainly not an important topic.
Water usage an important topic to discuss
Freshwater is a precious commodity on a global scale.
What needs to be remembered is that the water quantity on earth is a set total of 100% it doesn’t increase or decrease. If you take it out of the ecosystem (alter its path) it cannot be used elsewhere in the water cycle until it returns.
Every construction project undertaken (road building, housing development, etc.) has to determine its impact on the flow of water and how it will effect its natural path through the water cycle.
Modern aquaculture RAS systems are built primarily indoors, as this alleviates problems relating to water quality and water chemistry.
But this reduces the ability for water to return to the environment as the water is covered and thus reduces evaporation potential.
These recirculating systems all run at 90% or greater efficiency, which seems to make a sound statement.
However, although efficiency is great there is still a huge quantity of water taken, and held out, of the natural water cycle.
There is also a continual need to add more water to the systems, in order to keep the correct levels, for a consistent operation. And most importantly, there has to be a constant supply available to allow systems to be shut down and drained as the production cycle requires. This need to refill on demand puts additional pressures on water sources.
Moving the farms closer to markets
Where will the water come from and how will it impact residential water supplies?
Many major cities have to conserve water during the summer due to the water demands that residential property put on water supplies. In other areas water may be sourced from aquifers, these need to be heavily monitored to ensure that the environment is replenishing these underground water sources. Rivers are usually not the best option due to fluctuations in water level, turbidity and water chemistry.
Most land based operations will also need to utilize saltwater for the adult portion of life stage which ultimately requires being relatively close to a source of saltwater.
Saltwater is by far more abundant in the environment as it is the start and end point of the water cycle.
Problems with saltwater relate to pathogens and the ability to disinfect the water successfully.
Current RAS technology
Saltwater RAS is not a problem, it already exists. The problems relate to the requirements of a system.
It is very difficult to switch a system that runs freshwater to a saltwater system as the biofilter that strips and converts natural organic material has specific organisms to do the conversions in freshwater. If you add saltwater it can be very demanding on the biofilter and may lead to the bacteria being overwhelmed or killed.
This means that there needs to be two separate systems at each land based facility, one to grow the salmon through freshwater life stage and the other to do the saltwater portion.
The alternate option is to bypass the RAS system altogether and use a flow through method. This would involve:
- pumping seawater from depth to try and avoid plankton blooms and sea lice.
- disinfecting the water before usage
- disinfecting and cleaning the water after usage
- releasing the water back to the environment.
Disinfecting seawater can be a challenge as ozone, which is a highly effective disinfectant, cannot be utilized as it will produce bromide which is highly toxic. With ozone being a challenging disinfectant for seawater that leaves UV as the primary choice.
UV is also an excellent disinfectant, however, to run a whole system on UV disinfected saltwater that would require many large UV units which require a constant power supply. If the power supply is interrupted, most UV units will require time to start up and reheat the lamps. This is something that is not an option when a constant supply of water is required to maintain the system water levels.
The above does not include risks to what may happen if pumps break, the plant loses power, or the myriad of other problems that could occur, if the technology malfunctions.
Biosecurity and pathogen introduction
Seawater contains thousands of bacteria and viruses.
If the disinfection system for incoming water is not operating at the correct levels for full disinfection (malfunctions, bulbs blowing, bulbs operating below their capacity etc.) there is a potential to introduce harmful pathogens to the fish.
If a virus enters a system where fish are unvaccinated against said virus there will be mass die off.
Consider, also, the potential for sea lice to make their way in, if these parasites breach the system, fish treatments may also be required.
Although saltwater is successfully used in some hatcheries, the quantity of water required is far lower and thus requires smaller UV units.
Saltwater, in this case, is used as a buffer to water harness – it is not the primary water source and if there is a problem the saltwater can be turned off with no impact.
Conserve water usage
The UN predicts 5 billion people could be out of fresh water by 2050…
“To help manage competing demands for freshwater – whether to quench human thirst, water crops or produce electricity – the report recommended “working with nature, rather than against it” in a bid to make water use more efficient, cost-effective and healthier for people and the environment.” (link)
To require the estimated 4.16 billion litres to start these facilities and subsequently remove this quantity of water from the environment is an inconceivable notion. Particularly when there are solutions that work right now and do not cause water extraction issues.
Sustainable salmon farming in British Columbia
AROUND THE WEB:
World Water Development Report 2018