Low-head, roughing filters for enhancing recycle water treatment for aquaculture

The engineering aspects of producing walleye in recycle culture systems was studied. To recycle (i.e., reuse) the water, treatment processes were required to maintain water quality for the growth and health of the cultured walleye. The major treatment processes were aeration, clarification and nitrification. The goal of this research was to evaluate unit processes for recycle aquaculture systems that are amenable for converting abandoned water and waste water treatment plants into commercial sites for culturing walleye;A three-unit aquaculture pilot plant was equipped for growing walleye from fingerling to food-size fish. The growth of the walleye was observed in two closed-systems and a single-pass system for a period of two years. Normal operating conditions within the closed-systems required water replacement only for solids flushing and evaporation, which was approximately 5-10% of the system volume per day;Within the pilot plant, two clarification processes were used for removing organic solids from the recirculating water: sedimentation basins and roughing filters. The design of the pilot plant permitted the use of a range of hydraulic and solid loading rates to evaluate these clarification processes. Nitrification was evaluated using submerged, static-media, biological filters over a range of hydraulic and ammonia loading rates. Acceptable levels of oxygen and carbon dioxide were maintained by bubbling compressed air through diffusers in the culture tank and in separate columns;A study on nitrification and clarification within submerged, static-media filters indicated that: (1) biofilters had greater nitrification rates than roughing filters acting as their own clarifiers; (2) increased hydraulic loading rate tended to increase the oxygen and ammonia consumption rates within the biofilters; (3) increasing the rate captured suspended solids were removed from the clarification process improved nitrification within the biofilters and overall water quality;The generation and treatment of carbon dioxide within recycle aquaculture systems was reviewed, and design criteria for CO[subscript]2 control within recirculating systems were developed;This research demonstrated that walleye could be grown from fingerling (5-8 cm) to food-fish size in approximately two years within recirculating systems at an average temperature of 24°C

Evaluation of geotextile filtration applying coagulant and flocculant amendments for aquaculture biosolids dewatering and phosphorus removal

AbstractWastes contained in the microscreen backwash discharged from intensive recirculating aquaculture systems were removed and dewatered in simple geotextile bag filters. Three chemical coagulation aids (aluminum sulfate (alum), ferric chloride, and calcium hydroxide (hydrated lime)), were tested in combination with a long-chain polymer flocculation aid (HyChem CE 1950 at 25mg/L) to determine the most cost effective and efficient treatment combination. Three different coagulants were tested to determine if coagulant choice impacts nutrient and carbonaceous biochemical oxygen demand (cBOD5) leaching into the filtrate and the final composition of the bag-captured biosolids at the end of each period. If nutrient leaching into the bag filtrate could be minimized through coagulant selection, then geotextile bags could provide a convenient and effective method to dewater waste biosolids and provide them in a form that fish farmers could readily transport, store, or send for disposal.Results from replicate geotextile bag filter tests indicate that when alum, ferric chloride, and hydrated lime (plus a polymer) were amended to a backwash flow, both suspended solids capture and solids thickening were improved; i.e., total suspended solids removal rates of 95.8, 95.1, and 96.0%, respectively, were achieved along with final dewatered filter cake percent solids concentrations of 22.1, 19.3, and 20.9%, respectively. Alum, ferric chloride, and hydrated lime (plus a polymer) amended geotextile bags were not as effective in chemical oxygen demand (COD) and cBOD5 removal, resulting in removal rates of 69.6, 67.2, and 35.3%, respectively, and 56.6, 9.3, and −47.4%, respectively. Further, the use of lime as a coagulant resulted in filtrate COD and cBOD5 concentrations that exceeded inlet concentrations. Total nitrogen removal applying alum, ferric chloride, and lime were also less than effective, resulting in removal rates of 39.1, 46.7, and −8.9%, respectively. Filtrate total nitrogen concentrations were primarily in the inorganic form (total ammonia nitrogen) suggesting mineralization of ammonia as solids were stored within geotextile bags under anaerobic conditions. Alum, ferric chloride, and lime amended bags were moderately efficient at total phosphorus removal, resulting in removal rates of 67.6, 47.0, and 77.3%, respectively. Alum was identified as the most cost effective chemical for coagulation, but hydrated lime was the most effective at dissolved phosphorus precipitation and removal

Survey of large circular and octagonal tanks operated at Norwegian commercial smolt and post-smolt sites

AbstractA survey was conducted to determine the geometry, operating parameters, and other key features of large circular or octagonal culture tanks used to produce Atlantic salmon smolt and post-smolt at six major Norwegian Atlantic salmon production companies. A total of 55 large tanks were reported at seven land-based hatchery locations, i.e., averaging 7.9 (range of 4–12) large tanks per land-based site. In addition, one 21,000m3 floating fiberglass tank in sea was reported. Culture volume ranged from 500 to 1300m3 for each land-based tank. Most tanks were circular, but one site used octagonal tanks. Land-based tank diameters ranged from 14.5 to 20m diameter, whereas the floating tank was 40m diameter. Maximum tank depths ranged from 3.5 to 4.5m at land-based facilities, which produced diameter-to-average-depth ratios of 3.6:1 to 5.5:1m:m. The floating tank was much deeper at 20m, with a diameter-to-average-depth ratio of only 2.4:1m:m. All land-based tanks had floors sloping at 4.0–6.5% toward the tank center and various pipe configurations that penetrated the culture tank water volume at tank center. These pipes and sloping floors were used to reduce labor when removing dead fish and harvesting fish.Maximum flow ranged from 3 to 19m3/min per land-based tank, with 400m3/min at the floating tank, but tank flow was adjustable at most facilities. Land-based tanks were flushed at a mean hydraulic retention time (HRT) of 35–170min. Maximum feed load on each land-based tank ranged from 525 to 850kg/day, but the floating tank reached 3700kg/day. Almost half of the large tanks reported in this survey were installed or renovated since 2013, including the three tank systems with the highest flow rate per tank (greater than 17.6m3/min). These more recent tanks were operated at more rapid tank HRT’s, i.e., from 34.8 to 52.5min, than the 67–170min HRT typical of the large tanks built before 2013. In addition, flow per unit of feed load in land-based tanks that began operating before 2010 were lower (19–30m3 flow/kg feed) than in tanks that began operating later (33–40m3 flow/kg feed). In comparison, the floating tank operates at a maximum daily tank flow to feed load of 160m3 flow/kg feed, which is the least intensive of all tanks surveyed. Survey results suggest that the recently built tanks have been designed to operate at a reduced metabolic loading per unit of flow, a tendency that would improve water quality throughout the culture tank, all else equal. This trend is possible due to the ever increasing application of water recirculating systems

Ozonation of a recirculating rainbow trout culture system I. Effects on bacterial gill disease and heterotrophic bacteria

AbstractOzone was added to water in a recirculating rainbow trout (Oncorhynchus mykiss) culture system just before it entered the culture tanks in an attempt to reduce the numbers of heterotrophic bacteria in system water and on trout gills, and to prevent bacterial gill disease (BGD) in newly stocked fingerlings. During four 8-week trials, ozone was added to the system at a rate of 0.025 or 0.036–0.039 kg ozone/kg feed fed. In the control, where no ozone was added, and in previously published research, BGD outbreaks occurred within two weeks of stocking, and these outbreaks generally required three to four chemotherapeutant treatments to prevent high mortality. In three of four trials where ozone was added to the system, BGD outbreaks were prevented without chemical treatments, but the causative bacterium, Flavobacterium branchiophilum, still colonized gill tissue. The one ozone test where BGD outbreaks required two chemical treatments coincided with a malfunction of the ozone generator. Although ozonation did reduce BGD mortality, it failed in all trials to produce more than a one log10 reduction in numbers of heterotrophic bacteria in the system water or on gill tissue. Failure of the ozone to lower numbers of heterotrophic bacteria or to prevent the causative BGD bacterium from occurring on gills was attributed to the short exposure time to ozone residual (35 s contact chamber) and rapid loss of oxidation caused by levels of total suspended solids. Rationale for ozone's success at preventing BGD mortalities are not fully understood but may in part be due to improved water quality. Use of the lower ozone dosing rate (0.025 kg ozone/kg feed) appeared to provide the same benefits as the higher dosing rate (0.036–0.039 kg ozone/kg feed fed); however, the lower ozone dosing rate was less likely to produce a toxic ozone residual in the culture tank and would also reduce ozone equipment capital and operating costs

Iowa Climate Statement 2020: Will COVID-19 Lessons Help Us Survive Climate Change?

The current SARS-CoV2 pandemic is a social, humanitarian, and economic crisis that was predicted by experts but made worse by a failure to act proactively on those warnings. As scientists teaching and studying climate and its impacts, we believe there are three important lessons from the current pandemic that apply to our understanding of climate mitigation and adaptation in Iowa

Low-head, roughing filters for enhancing recycle water treatment for aquaculture

The engineering aspects of producing walleye in recycle culture systems was studied. To recycle (i.e., reuse) the water, treatment processes were required to maintain water quality for the growth and health of the cultured walleye. The major treatment processes were aeration, clarification and nitrification. The goal of this research was to evaluate unit processes for recycle aquaculture systems that are amenable for converting abandoned water and waste water treatment plants into commercial sites for culturing walleye;A three-unit aquaculture pilot plant was equipped for growing walleye from fingerling to food-size fish. The growth of the walleye was observed in two closed-systems and a single-pass system for a period of two years. Normal operating conditions within the closed-systems required water replacement only for solids flushing and evaporation, which was approximately 5-10% of the system volume per day;Within the pilot plant, two clarification processes were used for removing organic solids from the recirculating water: sedimentation basins and roughing filters. The design of the pilot plant permitted the use of a range of hydraulic and solid loading rates to evaluate these clarification processes. Nitrification was evaluated using submerged, static-media, biological filters over a range of hydraulic and ammonia loading rates. Acceptable levels of oxygen and carbon dioxide were maintained by bubbling compressed air through diffusers in the culture tank and in separate columns;A study on nitrification and clarification within submerged, static-media filters indicated that: (1) biofilters had greater nitrification rates than roughing filters acting as their own clarifiers; (2) increased hydraulic loading rate tended to increase the oxygen and ammonia consumption rates within the biofilters; (3) increasing the rate captured suspended solids were removed from the clarification process improved nitrification within the biofilters and overall water quality;The generation and treatment of carbon dioxide within recycle aquaculture systems was reviewed, and design criteria for CO[subscript]2 control within recirculating systems were developed;This research demonstrated that walleye could be grown from fingerling (5-8 cm) to food-fish size in approximately two years within recirculating systems at an average temperature of 24°C.</p

Influence of inlet and outlet placement on the hydrodynamics of culture tanks for Atlantic salmon

The salmon farming industry has recently shifted to larger culture tanks with greater water flows to optimize the land-based production, but tanks approaching 1000 m3 in volume create challenging hydrodynamics. This paper presents a computational study of four combinations of inlet and outlet designs of a commercial land-based aquaculture tank. Windows-based OpenFOAM solvers are used to solve the conservation equations for tank hydrodynamics with an implicit unsteady second-order Eulerian (finite volume) technique on unstructured hybrid meshes. The model is validated by the velocity measurements at discrete locations in the tank using acoustic doppler velocimetry. To understand the dispersion of biosolids in the tank, 500 particles with a uniform size of 200 µm are tracked in the Lagrangian frame. While the tank's Reynolds number varies between 2E6 - 3.5E6 depending on the flow exchange rate, the local Reynolds number at the inlet pipe is about 2E5 which discovers the drag-crisis phenomenon. The effect of inlet and outlet placement on the velocity, vorticity and turbulence is addressed. The existing tank design could be improved using the bottom-drain and corner-inlet options, which strengthens rotational flow with better uniformity. Such design change is also proved to provide better particle removal and thus ensure the improved self-cleaning ability of the tank.publishedVersio