Ammonia oxidation and oxygen consumption rate measurements in RAS at different alkalinities

Abstract

The need for environmentally friendly sustainable nutritious food has never been more imminent than today, with a need to increase the world´s animal-based food supply by 70% by 2050. By simply increasing the number of animals would do more harm than good. Fish are a great source of animal protein and an important source of nutrients especially for people in developmental countries however, wild capture fisheries have been stagnant for decades and today aquaculture is responsible around 50% of fish produced for human consumption. The leading method of farming has been extensive farming where fish are farmed at low densities, with low growth rates and flowthrough water however, a more sustainable way of farming and with increased production yields called recirculating aquacultural systems (RAS) is becoming more popular. Norway produces 50% of salmon sold worldwide. With salmon being of great value both financially and nutritionally it is important that their health and wellbeing are taken care of. If the RAS are not working at full potential this can result in accumulation of nitrogenous wastes like ammonia-nitrogen and nitrite-nitrogen, which are highly toxic to aquatic organisms. Biofilter within the RAS can break down these toxins through nitrification however, several environmental conditions affect the efficiency of the biofilters. One of the factors whose effects are not well understood is alkalinity. The aim of this thesis was to investigate what effects alkalinity has on nitrification and to make a protocol for measuring oxygen consumption during nitrification. Alkalinity levels of 70, 100 and 200 mg/L as CaCO3 were used with no apparent effect on nitrification or oxygen consumption. The only things found to effect nitrification rates were ammonia concentrations and biofilter maturation. Oxygen consumption measurements during nitrification were successful but they can not be used as an estimate of biofilter activity.