Assessing the suitability of a partial water reuse system for rearing juvenile Chinook salmon for stocking in Washington State.

To assess the suitability of water reuse technology for raising Pacific salmon Oncorhynchus spp. for stocking purposes, fish health and welfare were compared between two groups of juvenile Chinook salmon O. tshawytscha from the same spawn: one group was reared in a pilot partial water reuse system (circular tanks), and the other group was reared in a flow-through raceway. This observational study was carried out over a 21-week period in Washington State. Reuse and raceway fish were sampled repeatedly for pathogen screening and histopathology; fin erosion and whole-blood characteristics were also evaluated. By the study's end, no listed pathogens were isolated from either cohort, and survival was 99.3% and 99.0% in the reuse and raceway groups, respectively. Condition factor was 1.28 in raceway fish and 1.14 in reuse fish; this difference may have been attributable to occasional differences in feeding rates between the cohorts. Fin indices (i.e., length of the longest dorsal or caudal fin ray, standardized by fork length) were lower in reuse fish than in raceway fish, but fin erosion was not grossly apparent in either cohort. The most consistent histological lesion was gill epithelial hypertrophy in reuse fish; however, blood analyses did not suggest any corresponding physiological imbalances. Overall, results suggest that water reuse technology can be employed in rearing juvenile anadromous salmonids for stocking purposes.

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.