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At least 37 records · Page 2Linked to original sources
USGS2004

Validation of two dilution models to predict chloramine-T concentrations in aquaculture facility effluent

Accurate estimates of drug concentrations in hatchery effluent are critical to assess the environmental risk of hatchery drug discharge resulting from disease treatment. This study validated two dilution simple n models to estimate chloramine-T environmental introduction concentrations by comparing measured and predicted chloramine-T concentrations using the US Geological Survey's Upper Midwest Environmental Sciences Center aquaculture facility effluent as an example. The hydraulic characteristics of our treated raceway and effluent and the accuracy of our water flow rate measurements were confirmed with the marker dye rhodamine WT. We also used the rhodamine WT data to develop dilution models that would (1) estimate the chloramine-T concentration at a given time and location in the effluent system and (2) estimate the average chloramine-T concentration at a given location over the entire discharge period. To test our models, we predicted the chloramine-T concentration at two sample points based on effluent flow and the maintenance of chloramine-T at 20 mg/l for 60 min in the same raceway used with rhodamine WT. The effluent sample points selected (sample points A and B) represented 47 and 100% of the total effluent flow, respectively. Sample point B is-analogous to the discharge of a hatchery that does not have a detention lagoon, i.e. The sample site was downstream of the last dilution water addition following treatment. We then applied four chloramine-T flow-through treatments at 20mg/l for 60 min and measured the chloramine-T concentration in water samples collected every 15 min for about 180 min from the treated raceway and sample points A and B during and after application. The predicted chloramine-T concentration at each sampling interval was similar to the measured chloramine-T concentration at sample points A and B and was generally bounded by the measured 90% confidence intervals. The predicted aver,age chloramine-T concentrations at sample points A or B (2.8 and 1.3 mg/l, respectively) were not significantly different (P > 0.05) from the average measured chloramine-T concentrations (2.7 and 1.3 mg/l, respectively). The close agreement between our predicted and measured chloramine-T concentrations indicate either of the dilution models could be used to adequately predict the chloramine-T environmental introduction concentration in Upper Midwest Environmental Sciences Center effluent.

Aquacultural Engineering↗
USGS2005

Screening and evaluation of polymers as flocculation aids for the treatment of aquacultural effluents

As environmental regulations become more stringent, environmentally sound waste management and disposal are becoming increasingly more important in all aquaculture operations. One of the primary water quality parameters of concern is the suspended solids concentration in the discharged effluent. For example, EPA initially considered the establishment of numerical limitations for only one single pollutant: total suspended solids (TSS). For recirculation systems, the proposed TSS limitations would have applied to solids polishing or secondary solids removal technology. The new rules and regulations from EPA (August 23, 2004) require only qualitative TSS limits, in the form of solids control best management practices (BMP), allowing individual regional and site specific conditions to be addressed by existing state or regional programs through NPDES permits. In recirculation systems, microscreen filters are commonly used to remove the suspended solids from the process water. Further concentration of suspended solids from the backwash water of the microscreen filter could significantly reduce quantity of discharge water. And in some cases, the backwash water from microscreen filters needs to be further concentrated to minimize storage volume during over wintering for land disposal or other final disposal options. In addition, this may be required to meet local, state, and regional discharge water quality. The objective of this research was an initial screening of several commercially available polymers routinely used as coagulation-flocculation aids in the drinking and wastewater treatment industry and determination of their effectiveness for the treatment of aquaculture wastewater. Based on the results of the initial screening, a further evaluation of six polymers was conducted to estimate the optimum polymer dosage for flocculation of aquaculture microscreen effluent and overall solids removal efficiency. Results of these evaluations show TSS removal was close to 99% via settling, with final TSS values ranging from as low as 10-17 mg/L. Although not intended to be used for reactive phosphorus (RP) removal, RP was reduced by 92-95% by removing most of the TSS in the wastewater to approximately 1 mg/L-P. Dosage requirements were fairly uniform, requiring between 15 and 20 mg/L of polymer. Using these dosages, estimated costs range from $4.38 to $13.08 per metric tonne of feed. ?? 2005 Elsevier B.V. All rights reserved.

Aquacultural Engineering↗
USGS2006

Comparative performance of fixed-film biological filters: Application of reactor theory

Nitrification is classified as a two-step consecutive reaction where R1 represents the rate of formation of the intermediate product NO2-N and R2 represents the rate of formation of the final product NO3-N. The relative rates of R1 and R2 are influenced by reactor type characterized hydraulically as plug-flow, plug-flow with dispersion and mixed-flow. We develop substrate conversion models for fixed-film biofilters operating in the first-order kinetic regime based on application of chemical reactor theory. Reactor type, inlet conditions and the biofilm kinetic constants Ki (h-1) are used to predict changes in NH4-N, NO2-N, NO3-N and BOD5. The inhibiting effects of the latter on R1 and R2 were established based on the ?? relation, e.g.:{A formula is presented}where BOD5,max is the concentration that causes nitrification to cease and N is a variable relating Ki to increasing BOD5. Conversion models were incorporated in spreadsheet programs that provided steady-state concentrations of nitrogen and BOD5 at several points in a recirculating aquaculture system operating with input values for fish feed rate, reactor volume, microscreen performance, make-up and recirculating flow rates. When rate constants are standardized, spreadsheet use demonstrates plug-flow reactors provide higher rates of R1 and R2 than mixed-flow reactors thereby reducing volume requirements for target concentrations of NH4-N and NO2-N. The benefit provided by the plug-flow reactor varies with hydraulic residence time t as well as the effective vessel dispersion number, D/??L. Both reactor types are capable of providing net increases in NO2-N during treatment but the rate of decrease in the mixed-flow case falls well behind that predicted for plug-flow operation. We show the potential for a positive net change in NO2-N increases with decreases in the dimensionless ratios K2, (R2 )/K1,( R1 ) and [NO2-N]/[NH4-N] and when the product K1, (R1) t provides low to moderate NH4-N conversions. Maintaining high levels of the latter reduces the effective reactor utilization rate (%) defined here as (RNavg/RNmax)100 where RNavg is the mean reactive nitrogen concentration ([NH4-N] + [NO2-N]) within the reactor, and RNmax represents the feed concentration of the same. Low utilization rates provide a hedge against unexpected increases in substrate loading and reduce water pumping requirements but force use of elevated reactor volumes. Further ?? effects on R1 and R2 can be reduced through use of a tanks-in-series versus a single mixed-flow reactor configuration and by improving the solids removal efficiency of microscreen treatment.

Aquacultural Engineering↗
USGS2006

Limestone fluidized bed treatment of acid-impacted water at the Craig Brook National Fish Hatchery, Maine, USA

Decades of atmospheric acid deposition have resulted in widespread lake and river acidification in the northeastern U.S. Biological effects of acidification include increased mortality of sensitive aquatic species such as the endangered Atlantic salmon (Salmo salar). The purpose of this paper is to describe the development of a limestone-based fluidized bed system for the treatment of acid-impacted waters. The treatment system was tested at the Craig Brook National Fish Hatchery in East Orland, Maine over a period of 3 years. The product water from the treatment system was diluted with hatchery water to prepare water supplies with three different levels of alkalinity for testing of fish health and survival. Based on positive results from a prototype system used in the first year of the study, a larger demonstration system was used in the second and third years with the objective of decreasing operating costs. Carbon dioxide was used to accelerate limestone dissolution, and was the major factor in system performance, as evidenced by the model result: Alk = 72.84 ?? P(CO2)1/2; R2 = 0.975. No significant acidic incursions were noted for the control water over the course of the study. Had these incursions occurred, survivability in the untreated water would likely have been much more severely impacted. Treated water consistently provided elevated alkalinity and pH above that of the hatchery source water. ?? 2005 Elsevier B.V. All rights reserved.

Aquacultural Engineering↗
USGS2006

Design of a computerized, temperature-controlled, recirculating aquaria system

We built a recirculating aquaria system with computerized temperature control to maintain static temperatures, increase temperatures 1 ??C/day, and maintain diel temperature fluctuations up to 10 ??C. A LabVIEW program compared the temperature recorded by thermocouples in fish tanks to a desired set temperature and then calculated the amount of hot or cold water to add to tanks to reach or maintain the desired temperature. Intellifaucet?? three-way mixing valves controlled temperature of the input water and ensured that all fish tanks had the same turnover rate. The system was analyzed over a period of 50 days and was fully functional for 96% of that time. Six different temperature treatments were run simultaneously in 18, 72 L fish tanks and temperatures stayed within 0.5 ??C of set temperature. We used the system to determine the upper temperature tolerance of fishes, but it could be used in aquaculture, ecological studies, or other aquatic work where temperature control is required. ?? 2005 Elsevier B.V. All rights reserved.

Aquacultural Engineering↗
USGS2007

Minimizing noise in fiberglass aquaculture tanks: Noise reduction potential of various retrofits

Equipment used in intensive aquaculture systems, such as pumps and blowers can produce underwater sound levels and frequencies within the range of fish hearing. The impacts of underwater noise on fish are not well known, but limited research suggests that subjecting fish to noise could result in impairment of the auditory system, reduced growth rates, and increased stress. Consequently, reducing sound in fish tanks could result in advantages for cultured species and increased productivity for the aquaculture industry. The objective of this study was to evaluate the noise reduction potential of various retrofits to fiberglass fish culture tanks. The following structural changes were applied to tanks to reduce underwater noise: (1) inlet piping was suspended to avoid contact with the tank, (2) effluent piping was disconnected from a common drain line, (3) effluent piping was insulated beneath tanks, and (4) tanks were elevated on cement blocks and seated on insulated padding. Four combinations of the aforementioned structural changes were evaluated in duplicate and two tanks were left unchanged as controls. Control tanks had sound levels of 120.6 dB re 1 ??Pa. Each retrofit contributed to a reduction of underwater sound. As structural changes were combined, a cumulative reduction in sound level was observed. Tanks designed with a combination of retrofits had sound levels of 108.6 dB re 1 ??Pa, a four-fold reduction in sound pressure level. Sound frequency spectra indicated that the greatest sound reductions occurred between 2 and 100 Hz and demonstrated that nearby pumps and blowers created tonal frequencies that were transmitted into the tanks. The tank modifications used during this study were simple and inexpensive and could be applied to existing systems or considered when designing aquaculture facilities. ?? 2007 Elsevier B.V. All rights reserved.

Aquacultural Engineering↗
USGS2007

Use of avoidance response by rainbow trout to carbon dioxide for fish self-transfer between tanks

Convenient, economical, and reduced labor fish harvest and transfer systems are required to realize operating cost savings that can be achieved with the use of much larger and deeper circular culture tanks. To achieve these goals, we developed a new technology for transferring fish based on their avoidance behavior to elevated concentrations of dissolved carbon dioxide (CO2). We observed this behavioral response during controlled, replicated experiments that showed dissolved CO2 concentrations of 60-120 mg/L induced rainbow trout (Oncorhynchus mykiss) to swim out of their 11 m3 "growout" tank, through a transfer pipe carrying a flow with ???23 mg/L dissolved CO2, into a second 11 m3 "harvest" tank. The research was conducted using separate groups of rainbow trout held at commercially relevant densities (40-60 kg/m3). The average weight of fish ranged from 0.15 to 1.3 kg during the various trials. In all trials that used a constant flow of low CO2 water (???23 mg/L) entering the growout tank from the harvest tank, approximately 80-90% of the fish swam from the growout tank, through the transfer pipe, and into the harvest tank after the CO2 concentration in the growout tank had exceeded 60 mg/L. The fish that remained in the growout tank stayed within the area of relatively low CO2 water at the entrance of the transfer pipe. However, the rate of fish transfer from the growout tank to the harvest tank was more than doubled when the diameter of the transfer pipe was increased from 203 to 406 mm. To consistently achieve fish transfer efficiencies of 99%, water flow rate through the fish transfer pipe had to be reduced to 10-20% of the original flow just before the conclusion of each trial. Reducing the flow of relatively low CO2 water near the end of each fish transfer event, restricted the zone of relatively low CO2 water about the entrance of the fish transfer pipe, and provided the stimulus for all but a few remaining fish to swim out of the growout tank. Results indicate that the CO2 avoidance technique can provide a convenient, efficient, more economical, and reduced labor approach for fish transfer, especially in applications using large and well mixed circular culture tanks. ?? 2007 Elsevier B.V. All rights reserved.

Aquacultural Engineering↗
USGS2011

Comparative performance of CO 2 measuring methods: marine aquaculture recirculation system application

Many methods are available for the measurement of dissolved carbon dioxide in an aqueous environment. Standard titration is the typical field method for measuring dissolved CO 2 in aquaculture systems. However, titrimetric determination of dissolved CO 2 in marine water aquaculture systems is unsuitable because of the high dissolved solids, silicates, and other dissolved minerals that interfere with the determination. Other methods used to measure dissolved carbon dioxide in an aquaculture water included use of a wetted CO 2 probe analyzer, standard nomographic methods, and calculation by direct measurements of the water's pH, temperature, and alkalinity. The determination of dissolved CO 2 in saltwater based on partial pressure measurements and non-dispersive infra-red (NDIR) techniques with a CO 2 gas analyzer are widely employed for oceanic surveys of surface ocean CO 2 flux and are similar to the techniques employed with the head space unit (HSU) in this study. Dissolved carbon dioxide (DC) determination with the HSU using a infra-red gas analyzer (IRGA) was compared with titrimetric, nomographic, calculated, and probe measurements of CO 2 in freshwater and in saltwater with a salinity ranging from 5.0 to 30 ppt, and a CO 2 range from 8 to 50 mg/L. Differences in CO 2 measurements between duplicate HSUs (0.1–0.2 mg/L) were not statistically significant different. The coefficient of variation for the HSU readings averaged 1.85% which was better than the CO 2 probe (4.09%) and that for the titrimetric method (5.84%). In all low, medium and high salinity level trials HSU precision was good, averaging 3.39%. Differences existed between comparison testing of the CO 2 probe and HSU measurements with the CO 2 probe readings, on average, providing DC estimates that were higher than HSU estimates. Differences between HSU and titration based estimates of DC increased with salinity and reached a maximum at 32.2 ppt. These differences were statistically significant (P < 0.05) at all salinity levels greater than 0.3 ppt. Results indicated reliable replicated results from the head space unit with varying salinity and dissolved carbon dioxide concentrations.

Aquacultural Engineering↗
USGS2012

Carbon dioxide stripping in aquaculture -- part II: development of gas transfer models

The basic mass transfer equation for gases such as oxygen and carbon dioxide can be derived from integration of the driving force equation. Because of the physical characteristics of the gas transfer processes, slightly different models are used for aerators tested under the non steady-state procedures, than for packed columns, or weirs. It is suggested that the standard condition for carbon dioxide should be 20 °C, 1 atm, CCO 2 =20 mg/kg, and XCO 2 =0.000285. The selection of the standard condition for carbon dioxide based on a fixed mole fraction ensures that standardized carbon dioxide transfer rates will be comparable even though the value of C* CO 2 in the atmosphere is increasing with time. The computation of mass transfer for carbon dioxide is complicated by the impact of water depth and gas phase enrichment on the saturation concentration within the unit, although the importance of either factor depends strongly on the specific type of aerator. For some types of aerators, the most accurate gas phase model remains to be determined for carbon dioxide. The assumption that carbon dioxide can be treated as a non-reactive gas in packed columns may apply for cold acidic waters but not for warm alkaline waters.

Aquacultural Engineering↗
USGS2012

Carbon dioxide stripping in aquaculture -- part III: model verification

Based on conventional mass transfer models developed for oxygen, the use of the non-linear ASCE method, 2-point method, and one parameter linear-regression method were evaluated for carbon dioxide stripping data. For values of K L a CO 2 < approximately 1.5/h, the 2-point or ASCE method are a good fit to experimental data, but the fit breaks down at higher values of K L a CO 2 . How to correct K L a CO 2 for gas phase enrichment remains to be determined. The one-parameter linear regression model was used to vary the C* CO 2 over the test, but it did not result in a better fit to the experimental data when compared to the ASCE or fixed C* CO 2 assumptions.

Aquacultural Engineering↗
USGS2012

Carbon dioxide stripping in aquaculture. part 1: terminology and reporting

The removal of carbon dioxide gas in aquacultural systems is much more complex than for oxygen or nitrogen gas because of liquid reactions of carbon dioxide and their kinetics. Almost all published carbon dioxide removal information for aquaculture is based on the apparent removal value after the CO 2 (aq) + HOH ⇔ H 2 CO 3 reaction has reached equilibrium. The true carbon dioxide removal is larger than the apparent value, especially for high alkalinities and seawater. For low alkalinity freshwaters (<2000 μeq/kg), the difference between the true and apparent removal is small and can be ignored for many applications. Analytical and reporting standards are recommended to improve our understanding of carbon dioxide removal.

Aquacultural Engineering↗
USGS2016

Application of a fluidized bed reactor charged with aragonite for control of alkalinity, pH and carbon dioxide in marine recirculating aquaculture systems

Control of alkalinity, dissolved carbon dioxide (dCO 2 ), and pH are critical in marine recirculating aquaculture systems (RAS) in order to maintain health and maximize growth. A small-scale prototype aragonite sand filled fluidized bed reactor was tested under varying conditions of alkalinity and dCO 2 to develop and model the response of dCO 2 across the reactor. A large-scale reactor was then incorporated into an operating marine recirculating aquaculture system to observe the reactor as the system moved toward equilibrium. The relationship between alkalinity dCO 2 , and pH across the reactor are described by multiple regression equations. The change in dCO 2 across the small-scale reactor indicated a strong likelihood that an equilibrium alkalinity would be maintained by using a fluidized bed aragonite reactor. The large-scale reactor verified this observation and established equilibrium at an alkalinity of approximately 135 mg/L as CaCO 3 , dCO 2 of 9 mg/L, and a pH of 7.0 within 4 days that was stable during a 14 day test period. The fluidized bed aragonite reactor has the potential to simplify alkalinity and pH control, and aid in dCO 2 control in RAS design and operation. Aragonite sand, purchased in bulk, is less expensive than sodium bicarbonate and could reduce overall operating production costs.

Aquacultural Engineering↗
USGS2016

Phosphorus removal from aquaculture effluents at the Northeast Fishery Center in Lamar, Pennsylvania using iron oxide sorption media

Three different iron oxide-based sorption media samples were tested for removal of phosphorus (P) from fish hatchery effluents using fixed bed processing. Two of the media samples were derived from residuals produced by the treatment of acid mine drainage, which were then compared to granular ferric hydroxide (GFH), a commercially available sorption medium. All of the media types removed from 50 to 70% of the P from the incoming aquaculture wastewater over 70&ndash;175 days of operation without regeneration. In some of the sorption trials, the GFH media showed superior adsorption in the earlier stages of the trial, but the GFH appeared to reach saturation more quickly, so that media performance was similar &ndash; at about 60% removal of P &ndash; over a longer time period of 175 days. Media regeneration tests were also conducted for both the commercial and mine drainage media, and demonstrated longer term performance, with overall P removal of 50&ndash;55%, over 223 days of total operation, with the advantages of phosphorus recycle and media reuse.

Pennsylvania↗
USGS2016

Comparison of hydraulics and particle removal efficiencies in a mixed cell raceway and Burrows pond rearing system

We compared the hydrodynamics of replicate experimental mixed cell and replicate standard Burrows pond rearing systems at the Dworshak National Fish Hatchery, ID, in an effort to identify methods for improved solids removal. We measured and compared the hydraulic residence time, particle removal efficiency, and measures of velocity using several tools. Computational fluid dynamics was used first to characterize hydraulics in the proposed retrofit that included removal of the traditional Burrows pond dividing wall and establishment of four counter rotating cells with appropriate drains and inlet water jets. Hydraulic residence time was subsequently established in the four full scale test tanks using measures of conductivity of a salt tracer introduced into the systems both with and without fish present. Vertical and horizontal velocities were also measured with acoustic Doppler velocimetry in transects across each of the rearing systems. Finally, we introduced ABS sinking beads that simulated fish solids then followed the kinetics of their removal via the drains to establish relative purge rates. The mixed cell raceway provided higher mean velocities and a more uniform velocity distribution than did the Burrows pond. Vectors revealed well-defined, counter-rotating cells in the mixed cell raceway, and were likely contributing factors in achieving a relatively high particle removal efficiency-88.6% versus 8.0% during the test period. We speculate retrofits of rearing ponds to mixed cell systems will improve both the rearing environments for the fish and solids removal, improving the efficiency and bio-security of fish culture. We recommend further testing in hatchery production trials to evaluate fish physiology and growth.

Idaho↗
USGS2017

Investigating the influence of nitrate nitrogen on post-smolt Atlantic salmon Salmo salar reproductive physiology in water recirculation aquaculture systems

A major issue affecting land-based, closed containment Atlantic salmon Salmo salar growout production in water recirculation aquaculture systems (RAS) is precocious male maturation, which can negatively impact factors such as feed conversion, fillet yield, and product quality. Along with other water quality parameters, elevated nitrate nitrogen (NO 3 -N) has been shown to influence the reproductive development and endogenous sex steroid production in a number of aquatic animal species, including Atlantic salmon. We sought to determine whether elevated NO 3 -N in RAS can influence early maturation in post-smolt Atlantic salmon in an 8-month trial in replicated freshwater RAS. Post-smolt Atlantic salmon (102 ± 1 g) were stocked into six RAS, with three RAS randomly selected for dosing with high NO 3 -N (99 ± 1 mg/L) and three RAS set for low NO 3 -N (10 ± 0 mg/L). At 2-, 4-, 6-, and 8-months post-stocking, 5 fish were randomly sampled from each RAS, gonadosomatic index(GSI) data were collected, and plasma was sampled for 11-ketotestosterone (11-KT) quantification. At 4- and 8-months post-stocking, samples of culture tank and spring water (used as “makeup” or replacement water) were collected and tested for a suite of 42 hormonally active compounds using liquid chromatography/mass spectrometry , as well as for estrogenicity using the bioluminescent yeast estrogen screen (BLYES) reporter system. Finally, at 8-months post-stocking 8–9 salmon were sampled from each RAS for blood gas and chemistry analyses, and multiple organ tissues were sampled for histopathology evaluation. Overall, sexually mature males were highly prevalent in both NO 3 -N treatment groups by study’s end, and there did not appear to be an effect of NO 3 -N on male maturation prevalence based on grilse identification, GSI, and 11-KT results, indicating that other culture parameters likely instigated early maturation. No important differences were noted between treatment groups for whole blood gas and chemistry parameters, and no significant tissue changes were noted on histopathology. No hormones, hormone conjugates, or mycotoxins were detected in any water samples; phytoestrogens were generally detected at low levels but were unrelated to NO 3 -N treatment. Finally, low-level estrogenicity was detected in RAS water, but a NO 3 -N treatment effect could not be determined. The major findings of this study are i) the NO 3 -N treatments did not appear to be related to the observed male maturation, and ii) the majority of hormonally active compounds were not detectable in RAS water.

Aquacultural Engineering↗
USGS2017

Performance and application of a fluidized bed limestone reactor designed for control of alkalinity, hardness and pH at the Warm Springs Regional Fisheries Center

Springs serving the Warm Springs Regional Fisheries Center, Warm Springs, Georgia, have pH, alkalinity, and hardness levels thatlie under the range required for successful fish propagation while free CO 2 is well above allowable targets. We evaluate a pretreatment process that exploits limestone’s (CaCO 3 ) ability to react away hydrogen ions (H + ) and carbon dioxide (CO 2 ) while increasing alkalinity (HCO 3 − ) and calcium (Ca2+) concentrations, i.e. CaCO 3 + H + ↔ HCO 3 − + Ca 2+ CaCO 3 + CO 2 + H 2 O ↔ Ca 2+ + 2HCO 3 − Limestone sand was tested in both pilot and full scale fluidized bed reactors (CycloBio®). We first established the bed expansion characteristics of three commercial limestone products then evaluated the effect of hydraulic flux and bed height on dissolution rate of a single selected product (Type A16 × 120). Pilot scale testing at 18C showed limestone dissolution rates were relatively insensitive to flux over the range 1.51–3.03 m 3 /min/m 2 but were sensitive (P < 0.001; R 2 = 0.881) to changes in bed height (BH, cm) over the range 83–165 cm following the relation: (Alkalinity, mg/L) = 123.51 − (3788.76 (BH)). Differences between filtered and non-filtered alkalinity were small(P > 0.05) demonstrating that limestone was present in the reactor effluent primarily in the form of dissolved Ca(HCO 3 ) 2 . Effluent alkalinity exceeded our target level of 50 mg/L under most operating conditions evaluated with typical pilot scale values falling within the range of 90–100 mg/L despite influent concentrations of about 4 mg/L. Concurrently, CO 2 fell from an average of 50.6 mg/L to 8.3 mg/L (90%), providing for an increase in pH from 5.27 to a mean of 7.71. The ability of the test reactor to provide changes in water chemistry variables that exceeded required changes allowed for a dilution ratio of 0.6. Here, alkalinity still exceeded 50 mg/L, the CO 2 concentration remained well below our limit of 20 mg/L (15.4 mg/L) and the pH was near neutral (7.17). Applying the dilution ratio of 0.6 in a full scale treatment plant at the site reduced by 40% the volume of spring water that is directed through each of three parallel reactors that combined react away 49,000 kg of limestone/yr.

Aquacultural Engineering↗
USGS2000

Hydraulic characteristics of a rectangular mixed-cell rearing unit

We describe a fish rearing unit modification that establishes mixed flow reactor (MFR) behavior in a rectangular vessel so as to eliminate metabolite concentration gradients, increase current velocities and improve solids scour at low water exchange rates. A standard raceway section 14.5 m long was modified to create six counter-rotating mixed cells, each 2.4 m wide by 2.4 m long. Cells receive water from vertical pipe sections extending to the tank floor and positioned in the corners of the cells. Vertical pipe sections were fabricated with jet ports that direct water into the cells tangentially to establish rotary circulation. Water exits each cell through a centrally located floor drain. Hydraulic characteristics of the tank are described based on an analysis of residence time distribution, current velocities and cell-to-cell water exchange rates. The latter was calculated based on a proposed hydraulics model and tracer concentrations established at a steady state. Vessel dispersion numbers measured with water exchange rates of 1.0 and 1.3 per hour, indicate tank performance approximates that of a MFR with the active tank volume representing 77.9–100% of total tank volume. Water velocities measured at 216 stations averaged 0.14, 0.12 and 0.12 m/s for the tank surface, mid-depth and near bottom regions. The benthic shear stress calculated given surface velocity was 0.04 N/m 2 . This was sufficient to scour and purge fecal solids produced by 2010 kg of lake trout that averaged 44.3 cm in total length. Cell interaction was significant with cell-to-cell exchange rates averaging 3.9 times the tank inflow rate. Energy requirements of the rearing unit were kept low (1.32 m water gauge pressure; 6.7 W/m 3 ) through use of a large number of low velocity jets.

Aquacultural Engineering↗
USGS2003

Evaluation of chemical coagulation-flocculation aids for the removal of suspended solids and phosphorus from intensive recirculating aquaculture effluent discharge

An evaluation of two commonly used coagulation-flocculation aids (alum and ferric chloride) was conducted for the supernatant overflow from settling cones used to treat the effluent from microscreen filters in an intensive recirculating aquaculture system. In addition to determining the effectiveness of these aids in removing both suspended solids and phosphorus, a systematic testing of the variables normally encountered in the coagulation-flocculation process was performed. Tests were carried out to evaluate the dosages and conditions (mixing and flocculation stirring speeds, durations, and settling times) required to achieve optimum waste capture. The orthophosphate removal efficiency for alum and ferric chloride were 89 and 93%, respectively, at a dosage of 90 mg/l. Optimum turbidity removal was achieved with a 60 mg/l dosage for both alum and ferric chloride. Both alum and ferric. chloride demonstrated excellent removal of suspended solids from initial TSS values of approximately 100-10 mg/l at a dosage of 90 mg/l. Flocculation and mixing speed played only a minor role in the removal efficiencies for both orthophosphates and suspended solids. Both coagulation-flocculation aids also exhibited excellent settling characteristics, with the majority of the floc quickly settling out in the first 5 min. ?? 2003 Elsevier B.V. All rights reserved.

Aquacultural Engineering↗