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

Ozone is a strong oxidant, and its use in aquaculture has been shown to improve water quality and fish health. At present, it is predominantly used in freshwater systems due to the high risk of toxic residual oxidant exposure in brackish water and seawater. Here, we report the effects of ozone on Atlantic salmon (Salmo salar) post-smolts (~100 g), in a brackish water (12 ppt) flow-through system. Salmon were exposed to oxidation reduction potential concentrations of 250 mV (control), 280 mV (low), 350 mV (medium), 425 mV (high) and 500 mV (very high). The physiological impacts of ozone were characterized by blood biochemical profiling, histopathologic examination and gene expression analysis in skin and gills. Fish exposed to 425 mV and higher showed ≥33% cumulative mortality in less than 10 days. No significant mortalities were recorded in the remaining groups. The skin surface quality and the thickness of the dermal and epidermal layers were not significantly affected by the treatments. On the other hand, gill histopathology showed the adverse effects of increasing ozone doses and the changes were more pronounced in the group exposed to 350 mV and higher. Cases of gill damages such as necrosis, lamellar fusion and hypertrophy were prevalent in the high and very high groups. Expression profiling of key biomarkers for mucosal health supported the histology results, showing that gills were significantly more affected by higher ozone doses compared to the skin. Increasing ozone doses triggered anti-oxidative stress and inflammatory responses in the gills, where transcript levels of glutathione reductase, copper/zinc superoxide dismutase, interleukin 1ß and interleukin were significantly elevated. Heat shock protein 70 was significantly upregulated in the skin of fish exposed to 350 mV and higher. Bcl-2 associated x protein was the only gene marker that was significantly upregulated by increasing ozone doses in both mucosal tissues. In conclusion, the study revealed that short-term exposure to ozone at concentrations higher than 350 mV in salmon in brackish water resulted in significant health and welfare consequences, including mortality and gill damages. The results of the study will be valuable in developing water treatment protocols for salmon farming.

Denitrifying woodchip bioreactor and phosphorus filter pairing to minimize pollution swapping.

Pairing denitrifying woodchip bioreactors and phosphorus-sorbing filters provides a unique, engineered approach for dual nutrient removal from waters impaired with both nitrogen (N) and phosphorus (P). This column study aimed to test placement of two P-filter media (acid mine drainage treatment residuals and steel slag) relative to a denitrifying system to maximize N and P removal and minimize pollution swapping under varying flow conditions (i.e., woodchip column hydraulic retention times (HRTs) of 7.2, 18, and 51 h; P-filter HRTs of 7.6-59 min). Woodchip denitrification columns were placed either upstream or downstream of P-filters filled with either medium. The configuration with woodchip denitrifying systems placed upstream of the P-filters generally provided optimized dissolved P removal efficiencies and removal rates. The P-filters placed upstream of the woodchip columns exhibited better P removal than downstream-placed P-filters only under overly long (i.e., N-limited) retention times when highly reduced effluent exited the woodchip bioreactors. The paired configurations using mine drainage residuals provided significantly greater P removal than the steel slag P-filters (e.g., 25-133 versus 8.8-48 g P removed m-3 filter media d-1, respectively), but there were no significant differences in N removal between treatments (removal rates: 8.0-18 g N removed m-3 woodchips d-1; N removal efficiencies: 18-95% across all HRTs). The range of HRTs tested here resulted in various undesirable pollution swapping by-products from the denitrifying bioreactors: nitrite production when nitrate removal was not complete and sulfate reduction, chemical oxygen demand production and decreased pH during overly long retention times. The downstream P-filter placement provided a polishing step for removal of chemical oxygen demand and nitrite.

Denitrifying bioreactor clogging potential during wastewater treatment.

Chemoheterotrophic denitrification technologies using woodchips as a solid carbon source (i.e., woodchip bioreactors) have been widely trialed for treatment of diffuse-source agricultural nitrogen pollution. There is growing interest in the use of this simple, relatively low-cost biological wastewater treatment option in waters with relatively higher total suspended solids (TSS) and chemical oxygen demand (COD) such as aquaculture wastewater. This work: (1) evaluated hydraulic retention time (HRT) impacts on COD/TSS removal, and (2) assessed the potential for woodchip clogging under this wastewater chemistry. Four pilot-scale woodchip denitrification bioreactors operated for 267 d showed excellent TSS removal (>90%) which occurred primarily near the inlet, and that COD removal was maximized at lower HRTs (e.g., 56% removal efficiency and 25 g of COD removed per m3 of bioreactor per d at a 24 h HRT). However, influent wastewater took progressively longer to move into the woodchips likely due to a combination of (1) woodchip settling, (2) clogging due to removed wastewater solids and/or accumulated bacterial growth, and (3) the pulsed flow system pushing the chips away from the inlet. The bioreactor that received the highest loading rate experienced the most altered hydraulics. Statistically significant increases in woodchip P content over time in woodchip bags placed near the bioreactor outlets (0.03 vs 0.10%P2O5) and along the bioreactor floor (0.04 vs. 0.12%P2O5) confirmed wastewater solids were being removed and may pose a concern for subsequent nutrient mineralization and release. Nevertheless, the excellent nitrate-nitrogen and TSS removal along with notable COD removal indicated woodchip bioreactors are a viable water treatment technology for these types of wastewaters given they are used downstream of a filtration device.

The cost and effectiveness of solids thickening technologies for treating backwash and recovering nutrients from intensive aquaculture systems.

The cost and effectiveness of three solids thickening processes, i.e., gravity thickening settlers (GTS), inclined belt filters (IBF), geotextile bag filters (GBF), were individually evaluated with the biosolids backwash produced in intensive aquaculture systems equipped with microscreen drum filters and radial-flow settlers. The IBF produced the cleanest discharge and highest treatment efficiencies, likely reflecting the rapid efficiency with which solids are separated from wastewater. The GBF was the least effective process, i.e., GBF leachate contained the highest concentrations of TP, TN, and cBOD. However, GBF was most effective for sludge volume reduction. Capital cost estimates for an IBF were more than twice that of GTS and GBF of similar treatment capacity. The GTS had the lowest capital and annual operating cost estimates. The estimated annual operating cost of the GBF was orders of magnitude higher than the IBF and GTS, due to the high cost to replace bags.

Evaluation of a membrane biological reactor for reclaiming water, alkalinity, salts, phosphorus, and protein contained in a high-strength aquacultural wastewater.

The capacity of a membrane biological reactor to provide nitrification, denitrification, and enhanced biological phosphorus removal of a high-strength aquaculture backwash flow (control condition), or the same flow amended with 100mg/L of NO(3)-N and 3mg/L of dissolved P (test condition), was assessed using only endogenous carbon. Permeate TSS and cBOD(5) concentrations were <1mg/L under control and test conditions, achieving 99.97-100% removal efficiencies, respectively. Permeate TN concentrations were 1.8+/-0.5mg/L and 2.1+/-1.4 mg/L, while permeate TP concentrations were 0.05+/-0.01 mg/L and 0.10+/-0.03 mg/L, respectively, under control and test conditions. Our findings suggest that permeate flow could be reclaimed to recycle alkalinity, salts, and heat for fish culture and that the waste activated sludge does not produce metals concentrations that would prevent its land application (reclaiming phosphorus) or prevent its use as a protein source in animal feeds.