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

Abstract

For a recirculating aquaculture system (RAS), a passive water treatment system was designed for efficient discharge nutrient removal and water reuse in RAS production. Denitrification in a woodchip bioreactor filled with birch wood (Betula pendula) followed by sand filtration was introduced into a side-loop of an experimental RAS rearing rainbow trout (Oncorhynchus mykiss). Denitrification efficiency remained high (96%) throughout the experiment and reached a nitrogen removal rate of 15 g NO3-N m−3 per day. Sand filtration was used to remove dissolved and particulate matter and improve water quality before being returned to water circulation. To ensure the absence of harmful substances in the system, heavy metals were quantified. Additionally, off-flavor-inducing compounds were quantified in the circulating water and in fish flesh. Significantly higher concentrations of geosmin (GSM) (p<0.05) were observed in the controls compared to side-looped systems, but a similar effect was not observed in the case of 2-methylisoborneol (MIB). Among heavy metals, concentrations of Co (30 μg L−1), Ni (40 μg L−1), and Pb (140 μg L−1) decreased to below 10 μg L−1 in the side-loop water after the start-up of the system. Only low concentrations of Cu (5–30 μg L−1) were found in the rearing tank water, in both the side-loop and controls. The results indicated that this type of process design is suitable for safely producing fish of high quality.

Water quality monitoring in recirculating aquaculture systems

“…The most common basic water quality parameters, such as temperature, pH and DO, can be measured with portable instruments such as Multi 3410 (WTW GmbH) (Chun et al., 2018). Although portable alternatives are available, nitrite, nitrate and phosphate are often measured more accurately in a laboratory, using an ion‐exchange chromatograph and suppressed conductivity detector (e.g., Dionex DX‐500, Dionex ICS1600, Dionex Integrion HPIC; Chun et al., 2018; Lindholm‐Lehto et al., 2020, 2021).…”

Review: Brine Solution: Current Status, Future Management and Technology Development

“…A typical example is the conversion of nitrate content into ammonia and then N 2 by denitrifying bacteria [33]. Many groups have come up with woodchip bioreactors, known as a convenient treatment method for nitrate removal [34][35][36][37][38]. However, these techniques require the addition or attachment of electron-donating groups such as ethanol or acetate in an attempt to enhance the conversion efficiency.…”

Effectiveness of Filter Media Compositions on Water Quality, Growth and Survival Rate of Tilapia (Oreochromis niloticus) Cultured in Recirculation System

“…The RAS is a cultivation system that is able to improve water quality by operating a filtration system to treat water that has been used in the cultivation process so that the water can be reused (Ngoc et al, 2016;Hisano et al, 2021;Azevedo et al, 2018). The principle of RAS is to reuse water from cultivation activities so as to save water consumption (Lindholm-Lehto and Vielma, 2019). Processes carried out at RAS can also help reduce pollutant content through aquaculture wastewater treatment with installed filters (Bhargava, 2018).…”