Use of glucose (С6P12O6) for stimulation of heterotrophic nitrification processes in biofilters of recirculating aquaculture systems (RAS)

Abstract

Purpose.Investigate the possibility of using glucose (С6Н12О6) to stimulate heterotrophic nitrification processes in biofilters and reduce the content of ammonium nitrogen in the water of recirculating aquaculture systems (RAS). Methodology. The object of research was the processes of water purification in biofilters of RAS from nitrogen compounds harmful to fish. The subject of research is the rate of heterotrophic nitrification using glucose as a source of organic carbon to accelerate nitrification processes under conditions of critical ammonium nitrogen content in process water. The research was conducted in four experimental RAS of the Fisheries Laboratory of the Department of Aquaculture of NULES of Ukraine. During the experiment, the concentrations of ammonia-ammonium in the water of aqua systems were artificially increased to 2 mg/dm3 by adding ammonium chloride solution, and 10% glucose solution was added in the proportions of 1 cm3, 5 cm3 and 10 cm3 per 100 dm3 of process water. The content of nitrogen compounds in water was determined using the Ptero Test system (NО2-, NH3/NH4+). Evaluation of the effectiveness of biofiltration in different variants of the experiment was performed on the time of excretion of NH3/NH4+ and the physical condition of sterlet fry (Acipenser ruthenus), which acted as a test object. Findings.The effectiveness of using glucose solution as a biologically active substance to stimulate the excretion of ammonia-ammonium by bacteria of the RAS biofilter has been proved. The rate of decrease of the concentration of NH3-/NH4+ to an acceptable level (below 0.1 mg/dm3) in the experimental systems with 5 and 10 сm3 of glucose per 100 dm3 of water was 5 hours versus 7 hours in the control version and in the experimental system with 1 сm3 glucose per 100 dm3 of water. Originality. A study on the use of glucose to accelerate nitrification processes in biofilters of RAS under conditions of critical ammonia-ammonium content in water was conducted for the first time. PracticalValue. The proposed method of stimulating heterotrophic nitrification solves a number of problems associated with a sharp increase of the content of NH3/NH4+ in process water. The use of this method will allow to reduce the risk of death of cultivated aquatic organisms due to a sharp increase of the concentration of ammonia-ammonium in water during the period of establishment of biological balance or in emergency situations. At the same time, it should be taken into account that heterotrophic bacteria grow much faster than nitrifying ones and may outperform the latter in the competition for substrate area in biofilters, so the use of this method is advisable for a short time, if necessary to release process water from excess ammonia-ammonium. Keywords: RAS, biofilter, glucose, heterotrophicnitrification, sterlet.