Sensitive, accurate and rapid analysis of nitrite and nitrate is essential for maintaining healthy environments in aquaponics and aquaculture, particularly in closed-loop, recirculating aquaculture systems. Aquamonitrix® provides real-time, accuarte intervention-free monitoring, with distinct readings for nitrate and nitrite from the same sample.
Designed to remove solids and recycle water back to the fish culture tanks, closed containment or recirculated aquaculture systems (RASs) offer many advantages.
With reduced water requirements, the cultivation of marine species no longer requires a coastal location. In fact, warm-water species can be produced in more temperate climates, and fish farms can be sited almost anywhere, even in urban spaces. Compared with traditional pond and floating cage methods, the more controlled closed environment also reduces ecological risks such as the transmission of diseases to wild stock or dilution of genetic diversity as a result of interbreeding with escaped farm species.
However, sensitive, accurate and rapid analysis of nitrogen-containing nutrients is essential for maintaining healthy aquatic environments.
Aquamonitrix® is a revolutionary high-accuracy, analyser that provides distinct nitrate and nitrite measurements from the same sample in real-time. Recirculating aquaculture system (RAS) operators can use Aquamonitrix® to
- Monitor intake and recirculating water for nitrite on a real-time, near-continuous basis and react immediately to protect species health
- Monitor biofilters to ensure complete conversion to nitrate
- Gain the kind of real-time, high-frequency data required to investigate, understand and optimise the nitrogen cycle in recirculating aquatic systems
- Monitor effluent to demonstrate environmental compliance / react instantaneously to nitrate exceedances
Nitrite is poisonous to fish at all pH levels. Nitrite poisoning follows closely on the heels of ammonia as a major killer of aquaculture species.
Sources of nitrogen in aquaculture
- In aquaculture, nitrogen enters the system as protein in the feed.
- About 20 to 25% of this accumulates in the animal tissues. The remainder is excreted as ammonium and organic nitrogen by fish/aquatic species through their gills or as urine.
- Other sources of ammonia in the system include decaying organic substances such as dead animals or uneaten food
- Depending on the source, water may also contain nitrate pollution, typically as a result of sewage or agricultural sources
The risk to species survival and health
- Un-ionized ammonia (NH3) is toxic and can cause gill and organ damage to aquatic species and may cause death in concentrations as low as two parts-per-million (2 ppm/mg/l).
- Through conventional water treatment technology (precipitation, filtration and biological purification), the ammonia is converted to nitrate (NO3).
- In biological filter systems, nitrification occurs in a 2-step process via the aerobic conversion of ammonia to nitrite, followed by the aerobic conversion of nitrite to nitrate.
- The nitrite intermediate is poisonous to fish at all pH levels. Nitrite poisoning follows closely on the heels of ammonia as a major killer of aquaculture species.
- Nitrate is much less toxic than either ammonia or nitrite. However, high concentrations and long exposure times can reduce animal growth and decrease survival. Also, as explained below, nitrate accumulation is a problem in closed-loop systems.
When nitrite becomes a problem
- Nitrite problems can arise in closed culture systems due to insufficient, inefficient management and malfunctioning filtration systems.
- If nitrite levels exceed that which resident bacteria can rapidly convert to nitrate, a build–up of nitrite occurs, and brown blood disease is a risk.
- Nitrite enters the bloodstream through the gills and turns the blood to a chocolate-brown colour. Haemoglobin, which transports oxygen in the blood, combines with nitrite to form methemoglobin, which is incapable of oxygen transport. Brown blood cannot carry sufficient amounts of oxygen, and affected fish can suffocate despite adequate oxygen concentration in the water.
- Fish that are exposed to even low levels of nitrite for long periods of time suffer damage to their immune system and are prone to secondary diseases.
Monitoring nitrite and nitrate levels in real-time with Aquamonitrix (pictured above) will allow RAS operators to better protect species, yield quality and profitability.
Dealing with nitrate accumulation
- Water exchange is one strategy for dealing with nitrate accumulation is. However, there are environmental issues (algae growth/deoxygenation, etc) associated with the discharge of effluent containing high nitrate levels, particularly in nitrate sensitive zones.
- Some RAS units may incorporate a denitrification This involves the anaerobic conversion of nitrate to nitrogen gas. The most common wastewater denitrification systems are based on denitrification with heterotrophic bacteria and the addition of a carbon source – typically methanol. The nitrate is converted to nitrogen gas and the dissolved organic carbon is converted to CO2 and water
- Phytoremediation, e.g. aquaponics or hydroponics, is another strategy for dealing with nitrate
- In aquaponics, nitrate is removed by crops. According to the Institute for Systems Biology, the recommended level of nitrate in a stable aquaponics system is between 10 and 150 ppm depending on the type and number of fish and the amount of water they’re producing. If the nitrate levels are much lower, the plants won’t be getting the nutrients they need. On the other hand, if the nitrate level is above 150 parts per million ppm, there is a risk of ‘nutrient burn’ of the plant roots.
Understanding and controlling the problem
Aquamonitrix® provides lab-quality accuracy and precision, with real-time transmission of data by IoT to the user’s data management platform and/or centralised control infrastructure. This previously unobtainable level of real-time data on nitrate and nitrate provides RAS operators with an unprecedented ability to protect species while maximising yield quality and profitability.
Aquamonitrix® offers extremely stable calibration, with minimal need for intervention over long deployments. The analyser is portable and can be up and running within a couple of hours. Furthermore, it is easy to operate and service, with low requirements for specialist or technical skills, contributing to low lifetime costs.