Water quality in recirculating aquaculture system using woodchip denitrification and slow sand filtration

Abstract

In recirculating aquaculture system (RAS), ammonium excreted by the fish is typically transformed to less toxic nitrate by microbial activity in bioreactors. However, nitrate-nitrogen load can be harmful for the receiving water body when released from the RAS facility. A new type of water treatment system for a RAS was designed, including a passive woodchip denitrification followed by a sand filtration introduced into a side-loop of an experimental RAS, rearing rainbow trout (Oncorhynchus mykiss). In the process, woodchips acted as a carbon source for the denitrification, aiming at a simultaneous nitrogen removal and reduction of water consumption while sand filtration was used to remove organic matter and recondition the circulating water. A variety of chemical analyses and toxicological tests were performed to study the suitability of the process and to ensure the absence of harmful or toxic substances in the system. The results did not show increased toxicity, and no increased mortality was reported for the raised species. After the start-up of the system, the concentrations of fatty acids (e.g., hexadecanoic acid <LOD-1.21 mg L −1) and heavy metals (e.g., Cd < LOD-0.45 μg L −1 , Pb < LOD-14 μg L −1) remained at very low levels and below those of known toxic effects. In the beginning of the experiment, good denitrification efficiency was achieved, but it declined after 1 month, showing the need for improved stability and dimensioning of the application. Keywords Gas chromatography (GC). Heavy metals. Inductively coupled plasma optical emission spectrometry (ICP-OES). Inductively coupled plasma mass chromatography (ICP-MS). Ion chromatography (IC). Rainbow trout. Recirculating aquaculture system (RAS)

Multi-Approach Assessment for Stress Evaluation in Rainbow Trout Females, Oncorhynchus mykiss (Walbaum, 1792) from Three Different Farms during the Summer Season

“…During summer, stress due to improper water temperatures and low dissolved oxygen levels is an increasingly common issue, severely affecting the growth performances of rainbow trout [ 6 , 22 ]. The data obtained in our study regarding the physicochemical parameters of the water in the three farms are in accordance with other studies [ 40 , 41 , 42 , 43 , 44 ], which follow the environmental parameters necessary for the normal development of rainbow trout. When allowed to behaviorally thermoregulate, rainbow trout have a mean preferred temperature of 16 °C but occupy a temperature range between 13 and 19 °C when oxygen is not limited [ 45 ].…”

Efficient water treatment achieved in recirculating aquaculture system using woodchip denitrification and slow sand filtration

“…The experiment was conducted by using randomly allocated duplicate systems. In total, four individual RASs were used which contained components described in detail in Pulkkinen et al (2018) and in Lindholm-Lehto et al (2020).…”

“…Woodchips contain a high C/N ratio, acting as a good carbon source in anoxic conditions (Warneke et al 2011). In RAS applications, denitrification utilizing woodchips as a carbon source has occasionally been reported in small experimental (Lepine et al 2020;Lindholm-Lehto et al 2020), pilot scale (von Ahnen et al 2019), and full-scale applications (von Ahnen et al 2018;Lepine et al 2018).…”

“…In our previous study (Lindholm-Lehto et al 2020), we showed that a passive water treatment loop with denitrification in a woodchip bioreactor followed by sand infiltration was a suitable treatment for regenerating system effluent into intake water. In this study, the aim was to identify the optimal process design to achieve a stable nitrogen removal efficiency for a longer period.…”

The Effect of Filtration with Natural Esker Sand on the Removal of Organic Carbon and Suspended Solids from the Effluent of Experimental Recirculating Aquaculture Systems

“…Before infiltration through the sand material, the water was first led to a woodchip bioreactor. The woodchip bioreactor containing unbarked silver birch (Betula Pendula) woodchips (< 5 mm) acted as a carbon source for denitrification, aiming at nitrogen removal from the circulating system (Lindholm-Lehto et al 2020;Pulkkinen et al 2018).…”