Ozonation control and effects of ozone on water quality in recirculating aquaculture systems

Abstract

To address the undesired effect of chemotherapeutants in aquaculture, ozone has been suggested as an alternative to improve water quality. To ensure safe and robust treatment, it is vital to define the ozone demand and ozone kinetics of the specific water matrix to avoid ozone overdose. Different ozone dosages were applied to water in freshwater recirculating aquaculture systems (RAS). Experiments were performed to investigate ozone kinetics and demand, and to evaluate the effects on the water quality, particularly in relation to fluorescent organic matter. This study aimed at predicting a suitable ozone dosage for water treatment based on daily ozone demand via laboratory studies. These ozone dosages will be eventually applied and maintained at these levels in pilot-scale RAS to verify predictions. Selected water quality parameters were measured, including natural fluorescence and organic compound concentration changes during ozonation. Ozone reactions were described by first order kinetics. Organic matter, assessed as chemical oxygen demand and fluorescence, decreased by 25% (low O), 30% (middle O) and 53% (high O), while water transmittance improved by 15% over an 8-day period. No fish mortality was observed. Overall, this study confirms that ozone can improve RAS water quality, provides a better understanding of the ozone decay mechanisms that can be used to define further safe ozone treatment margins, and that fluorescence could be used as a monitoring tool to control ozone. This study might be used as a tool to design ozone systems for full-scale RAS by analysing water sample from the specific RAS in the laboratory.

Oxidative Chemical Stressors Alter the Physiological State of the Nasal Olfactory Mucosa of Atlantic Salmon

“…Exogenous ROS may come from various sources, and their impacts on redox status have consequences on cell viability, activation, proliferation, and organ function. Farmed fish encounter an increased flow of exogenous ROS several times during a lifetime, as many husbandry practices employ ROS-generating compounds either as a form of disinfectant or water treatment, or as a chemotherapeutant [7][8][9][10][11]. The antimicrobial activity of ROS towards opportunistic and pathogenic microorganisms underlines their use in providing fish with a favourable rearing environment [12].…”

The Effects of Ozone on Atlantic Salmon Post-Smolt in Brackish Water—Establishing Welfare Indicators and Thresholds

“…It is highly unstable, making it a potent oxidizing agent with high germicidal effectiveness and is thus ideal for use in water treatment. Ozone has been an integral component of RAS over the years, and the benefits on improved water quality, biosecurity and fish health are well documented [ 4 , 5 , 6 , 7 , 8 , 9 ]. This strong oxidant improves water quality by reducing organic matter, chemical oxygen demand, dissolved organic carbon, fine particulates, nitrite, water color or even hydrogen sulphide [ 4 , 7 , 10 , 11 ].…”

“…The use of ozone in brackish and seawater systems presents a challenge as ozone leads to the formation of byproducts (total residual oxidants (TROs)). Ozone dosage and control is still challenging due to limited options in measuring technologies for ozone and TROs [ 8 , 14 ]. Ozone measurements in industrial aquaculture facilities are often not standardized.…”

“…Ozone measurements in industrial aquaculture facilities are often not standardized. The most common measurements for ozone level are expressed as either as oxidation-reduction potential (ORP) in millivolts (mV), water transparency/turbidity in varying units or TROs as µg L −1 of chlorine (Cl 2 ) [ 8 ]. Spiliotopoulou [ 6 ] presented a new approach by using fluorescence organic matter degradation for monitoring ozone, which is presently not used commercially.…”

Natural fluorescence emission – an indirect measurement of applied ozone dosages to remove pharmaceuticals in biologically treated wastewater

“…Fluorescence has occasionally been used for off-and online monitoring in water treatment applications to optimize processes [25] and to identify deteriorating agents [26]. It is able to determine rapidly and accurately DOM in aquatic environments [19,[26][27][28][29][30][31][32][33][34] total organic carbon (TOC) [33], biological oxygen demand (BOD) [35], phosphate, nitrogen-based compounds [36] and microbial abundances [37]. A recent study suggested a method to correlate the fluorescence degradation upon ozonation with the delivered ozone dosage in recirculating aquaculture systems [38].…”