Control of off-flavor compounds in a full-scale recirculating aquaculture system rearing rainbow trout Oncorhynchus mykiss

Figures & data

Figure 1. Concentrations of ammonium-N (NH₄-N, mg L⁻¹), nitrite-N (NO₂-N, mg L⁻¹), nitrate-N (NO₃-N, mg L⁻¹, y-axis on the right-hand side), and turbidity (NTU) in the header tank water.

Figure 2. Addition of PAA, H₂O₂, and O₃ over the course of experiment. PAA1 was added (15 L d⁻¹, 5.2•10⁻³-5.4•10⁻³ L PAA m⁻³) into the inlet water and PAA2 (4–6 L d⁻¹, 1.4•10⁻³-2.1•10⁻³ L PAA m⁻³) into the aeration system of the depuration tanks. H₂O₂ was added 20–200 L d⁻¹ (0.00009–0.0009 L H₂O₂ m⁻³) to the circulating water and O₃ 30–50 L d⁻¹ (0.010–0.018 L O₃ m⁻³) to the inlet water.

Figure 3. Concentrations of GSM and MIB (n = 4, ± SD, ng L⁻¹) in the circulating water after the biofilter. An H₂O₂ solution was applied, with a dosage of 0–170 L d⁻¹. PAA was applied to the inlet water 15 L d⁻¹ (PAA1) and 4–6 L d⁻¹ (PAA2) into the aeration system of the depuration tanks.

Figure 4. Concentrations of GSM and MIB (n = 4, ± SD, ng L⁻¹) in the circulating water from the header tanks before entering the rearing tanks. An H₂O₂ solution was applied, with a dosage of 0–170 L d⁻¹. PAA was applied to the inlet water 15 L d⁻¹ (PAA1) and 4–6 L d⁻¹ (PAA2) into the aeration system of the depuration tanks.

Table 1. Concentrations of GSM and MIB (ng L⁻¹, n = 4, ± SD) in untreated inlet water from Lake Unnukka and in depuration tank water after 1 and 7 d

Sample	Date	GSM, ng L^−1	MIB, ng L^−1
Lake water	17 September	<LOQ	12.2
Lake water	23 October	5.5 ± 0.1	9.2 ± 1.2
Lake water	15 November	4.6 ± 1.5	4.9 ± 0.2
Depuration 1 d	17 September	4.4 ± 2.2	15.3 ± 5.7
Depuration 7 d	23 September	3.6 ± 1.9	14.3 ± 4.5
Depuration 1 d	22 November	9.6 ± 0.8	9.7 ± 2.7
Depuration 7 d	27 November	9.9 ± 2.4	4.3 ± 0.8

<LOQ denotes below level of detection.

LOQ 1.6 ng L⁻¹ (MIB), 2.8 ng L⁻¹ (GSM).

Figure 5. Concentrations of GSM and MIB (n = 4, ± SD, ng L⁻¹) in the circulating water after the rearing tanks. An H₂O₂ solution was applied with a dosage of 0–200 L d⁻¹ to the circulating water (2500 L s⁻¹) and ozone (O₃) 0–50 L d⁻¹ to the inlet water (32–33 L s⁻¹).

Table 2. Linear regression correlations between different H₂O₂ additions with GSM and MIB concentrations

Sample	Weeks of experiment	Equation	R^2	p Value
GSM after the rearing tanks	14	y = −0.0706x + 21.753	0.166	0.043
MIB after the rearing tanks	14	y = −0.1813x + 45.922	0.316	0.003
GSM after the biofilters	9	y = 0.0148x + 10.102	0.005	ns
MIB after the biofilters	9	y = −0.2692x + 60.564	0.435	0.01
GSM from the header tank	10	y = 0.1043x − 2.005	0.201	ns
MIB from the header tank	10	y = −0.0076x + 17.032	0.002	ns

The significance level was set at 0.05.

ns, not significant.