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1.
Fine media fluidized bed biofilters (FBB) have some unique characteristics, which become very important when extremely high water quality is required. They provide greater surface area per unit volume than other fixed film biofilters and are capable of operating as a plug flow on the liquid phase and mixed flow on the biological phase type reactor. As the concentration of pollutants decreases in an aquaculture system, the removal rate per unit surface area in a biofilter decreases, hence being able to obtain very high surface areas per unit cost becomes critical. As the concentration further decreases, conventional bioreactors that are either, mixed flow biological phase and mixed flow liquid phase (i.e. moving bed type reactor), or plug flow liquid and fixed biological phase (trickling filter or submerged filter) reach the minimum substrate concentration (SMin), below which the bacteria cannot grow under steady state conditions. However, in a fine media FBB the discharge concentration can be below SMin. This allows filters to be designed and operated in commercial aquaculture settings with over 90% removal of NH3, and related biochemical oxygen demand (BOD) per pass. Fine media FBBs can be designed and operated for biological removal of 99.95% of slow biodegrading refractory organic pollutants like methyl tertiary butyl ether (MTBE) in a single pass with discharge concentrations <1 ppb (inlet 2000 ppb, 20 min contact time, SMin = 20 ppb). The details of how and why these high performances at low concentrations are possible and why this oligotrophic water quality is desirable for maturation and larva rearing will be discussed.  相似文献   

2.
A partial-reuse system for coldwater aquaculture   总被引：7，自引：0，他引：7  
A model partial-reuse system is described that provides an alternative to salmonid production in serial-reuse raceway systems and has potential application in other fish-culture situations. The partial-reuse system contained three 10 m3 circular ‘Cornell-type’ dual-drain culture tanks. The side-wall discharge from the culture tanks was treated across a microscreen drum filter, then the water was pumped to the head of the system where dissolved carbon dioxide (CO2) stripping and pure oxygen (O2) supplementation took place before the water returned to the culture tanks. Dilution with make-up water controlled accumulations of total ammonia nitrogen (TAN). An automatic pH control system that modulated the stripping column fan ‘on’ and ‘off’ was used to limit the fractions of CO2 and unionized ammonia nitrogen (NH3---N). The partial-reuse system was evaluated during the culture of eight separate cohorts of advanced fingerlings, i.e., Arctic char, rainbow trout, and an all female brook trout × Arctic char hybrid. The fish performed well, even under intensive conditions, which were indicated by dissolved O2 consumption across the culture tank that went as high as 13 mg/L and fish-culture densities that were often between 100 and 148 kg/m3. Over all cohorts, feed conversion rates ranged from 1.0 to 1.3, specific growth rates (SGR) ranged from 1.32 to 2.45% body weight per day, and thermal growth coefficients ranged from 0.00132 to 0.00218. The partial-reuse system maintained safe water quality in all cases except for the first cohort—when the stripping column fan failed. The ‘Cornell-type’ dual-drain tank was found to rapidly (within only 1–2 min) and gently concentrate and flush approximately 68–88% (79% overall average) of the TSS produced daily within only 12–18% of the tank’s total water flow. Mean TSS concentrations discharged through the three culture tanks’ bottom-center drains (average of 17.1 mg/L) was 8.7 times greater than the TSS concentration discharged through the three culture tanks’ side-wall drains (average of 2.2 mg/L). Overall, approximately 82% of the TSS produced in the partial-reuse system was captured in an off-line settling tank, which is better TSS removal than others have estimated for serial-reuse systems (approximately 25–50%). For the two cohorts of rainbow trout, the partial-reuse system sustained a production level of 35–45 kg per year of fish for every 1 L/min of make-up water, which is approximately six to seven times greater than the typical 6 kg per year of trout produced for every 1 L/min of water in Idaho serial-reuse raceway systems.  相似文献   

3.
A direct method for measuring the 5-day biochemical oxygen demand (BOD5) of aquaculture samples that does not require sample dilution or bacterial and nutrient enrichment was evaluated. The regression coefficient (R2) between the direct method and the standard method for the analyses of 32 samples from catfish ponds was 0.996. The slope of the regression line did not differ from 1.0 or the Y-intercept from 0.0 at P = 0.05. Thus, there was almost perfect agreement between the two methods. The control limits (three standard deviations of the mean) for a standard solution containing 15 mg/L each of glutamic acid and glucose were 17.4 and 20.4 mg/L. The precision of the two methods, based on eight replicate analyses of four pond water samples did not differ at P = 0.05.  相似文献   

4.
This paper describes the performance characteristics of an industrial-scale air-driven rotating biological contactor (RBC) installed in a recirculating aquaculture system (RAS) rearing tilapia at 28 °C. This three-staged RBC system was configured with stages 1 and 2 possessing approximately the same total surface area and stage 3 having approximately 25% smaller. The total surface area provided by the RBC equaled 13,380 m2. Ammonia removal efficiency averaged 31.5% per pass for all systems examined, which equated to an average (± standard deviation) total ammonia nitrogen (TAN) areal removal rate of 0.43 ± 0.16 g/m2/day. First-order ammonia removal rate (K1) constants for stages 1–3 were 2.4, 1.5, and 3.0 h−1, respectively. The nitrite first-order rate constants (K2) were higher, averaging 16.2 h−1 for stage 1, 7.7 h−1 for stage 2, and 9.0 h−1 stage 3. Dissolved organic carbon (DOC) levels decreased an averaged 6.6% per pass across the RBC. Concurrently, increasing influent DOC concentrations decreased ammonia removal efficiency. With respect to dissolved gas conditioning, the RBC system reduced carbon dioxide concentrations approximately 39% as the water flowed through the vessel. The cumulative feed burden – describes the mass of food delivered to the system per unit volume of freshwater added to the system daily – ranged between 5.5 and 7.3 kg feed/m3 of freshwater; however, there was no detectable relationship between the feed loading rate and ammonia oxidation performance.  相似文献   

5.
Impact of ozonation on water quality in marine recirculation systems   总被引：8，自引：0，他引：8  
Ozone (O3) is a powerful oxidant and is becoming popular in various aquaculture systems for disinfection and improving water quality by oxidation of inorganic and/or organic compounds. However, the use of ozone in marine-based aquaculture systems has been limited because of the potential to form bromate, which is formed during the oxidation of naturally occurring bromide by ozone. Because bromate is a human carcinogen, there are concerns with its chronic impact on fish health. In addition, the use of O3 is hindered by lack of quantitative as well as qualitative design and performance information on O3 for recirculating systems. This study investigated the application of ozonation to control pathogens and enhance the process water quality in a recirculating aquaculture system while minimizing bromate formation. A field scale monitoring program was conducted on process water quality from Atlantic halibut (Hippoglossus hippoglossus) recirculating systems. Ozonated modules showed reduction of 15% total organic carbon (TOC) and less than 25 μg/l bromate concentration was formed. In addition, ozonated modules showed reduction in nitrate, color and suspended solids, as compared to those that did not use ozone. The results of this study elucidates the formation of bromate in marine water recirculation systems.  相似文献   

6.
Data collected from 45 commercial channel catfish, Ictalurus punctatus, ponds were used to develop empirical models predicting sediment oxygen demand (SOD). Seven acceptable models were combined with a Monte-Carlo sampling distribution to predict industry-wide sediment oxygen demand (SODi). The SODi values obtained from the best equation were used in simulations to assess the effect of diurnally varying water column dissolved oxygen (DO) concentrations on SOD and the effect of pond water depth on the contribution of SOD to overall pond respiration. Estimated SODi ranged from 62 to 962 mg m−2 h−1, with a mean of 478 mg m−2 h−1. There was a 95% probability of mean SODi being ≥700 mg m−2 h−1. The effects of diurnal variation in DO concentration in the water column on expression of SOD was modeled by combining maximum SODi, an empirical relationship between DO and SOD, and simulated pond DO concentrations. At DO concentrations >15 mg l−1, diel SOD in catfish ponds exceeded 20 g O2 m−2 day−1. But when average diel DO was <4 mg l−1 and the range of DO concentration was 6–8 mg l−1, SOD decreased to 13 g O2 m−2 day−1 because DO availability limited the full expression of potential SOD. Respiration totals for sediment (average SODi), plankton, and fish respiration were calculated for pond water depths ranging from 0.25 to 4 m. Although whole-pond respiration increases as pond depth increases, the proportion of total respiration represented by sediment decreased from 48 to 10% by increasing water depth over this range. The results of these studies show that SOD is a major component of total pond respiration and that certain management practices can affect the impact of SOD on pond oxygen budgets. Mixing ponds during daylight hours, either mechanically or by orienting ponds for maximum wind fetch, will increase oxygen supply to sediments, thereby allowing maximum expression of SOD and maximum mineralization of sediment organic matter. Given a mixed condition caused by wind or other artificial means, the construction of deeper ponds increases the total mass of DO available for all respiration, causing nighttime DO concentrations to decline at a slower rate, reducing the need for supplemental aeration. Because a pond’s water volume decreases over time from sediment accumulation, annual aeration costs will increase with pond age. Constructing ponds with greater initial depth will therefore reduce long-term cost of aeration, allow more flexible management of pond water budget, and reduce the long-term expense associated with pond reconstruction.  相似文献   

7.
Aerobic biological filtration systems employing nitrifying bacteria to remediate excess ammonia and nitrite concentrations are common components of recirculating aquaculture systems (RAS). However, significant water exchange may still be necessary to reduce nitrate concentrations to acceptable levels unless denitrification systems are included in the RAS design. This study evaluated the design of a full scale denitrification reactor in a commercial culture RAS application. Four carbon sources were evaluated including methanol, acetic acid, molasses and Cerelose™, a hydrolyzed starch, to determine their applicability under commercial culture conditions and to determine if any of these carbon sources encouraged the production of two common “off-flavor” compounds, 2-methyisoborneol (MIB) or geosmin. The denitrification design consisted of a 1.89 m3 covered conical bottom polyethylene tank containing 1.0 m3 media through which water up-flowed at a rate of 10 lpm. A commercial aquaculture system housing 6 metric tonnes of Siberian sturgeon was used to generate nitrate through nitrification in a moving bed biological filter. All four carbon sources were able to effectively reduce nitrate to near zero concentrations from influent concentrations ranging from 11 to 57 mg/l NO3–N, and the maximum daily denitrification rate was 670–680 g nitrogen removed/m3 media/day, regardless of the carbon source. Although nitrite production was not a problem once the reactors achieved a constant effluent nitrate, ammonia production was a significant problem for units fed molasses and to a less extent Cerelose™. Maximum measured ammonia concentrations in the reactor effluents for methanol, vinegar, Cerelose™ and molasses were 1.62 ± 0.10, 2.83 ± 0.17, 4.55 ± 0.45 and 5.25 ± 1.26 mg/l NH3–N, respectively. Turbidity production was significantly increased in reactors fed molasses and to a less extent Cerelose™. Concentrations of geosmin and MIB were not significantly increased in any of the denitrification reactors, regardless of carbon source. Because of its very low cost compared to the other sources tested, molasses may be an attractive carbon source for denitrification if issues of ammonia production, turbidity and foaming can be resolved.  相似文献   

8.
Water recirculating systems have been used in the shellfish industry for depuration and wet-storage. Knowledge of shellfish excretion characteristics is critical to recirculating system design. In this study, the excretion rate of total ammonia nitrogen (TAN), total Kjeldahl nitrogen (TKN), and 5-day biochemical oxygen demand (BOD5) from Manila clams (Tapes philippinarum) were investigated under both laboratory and commercial conditions. The laboratory tests were conducted under temperatures ranging from 3 to 30°C. The experimental results showed that temperature was a key factor in determining the excretion rate of all the above parameters. The relationship between TAN excretion rate (RTAN) and temperature (T) can be represented by an exponential function (RTAN=0.57×1.25T). For the temperature range between 3 and 20°C, the daily mean excretion rates of TAN, TKN and BOD5 ranged between 1.5–46.1, 4.8–131.0 and 57.4–219.4 mg per kilogram of the clams (wet weight with shell on), respectively. There were linear correlations between TAN, TKN and BOD5 production rates. The data presented in this paper can be used to estimate waste generation from a given shellfish processing operation and to size the waste treatment components for a recirculating depuration (or wet-storage) system.  相似文献   

9.
After settling pretreatment, the primary sludge wastewaters from a fish hatchery were treated in three five-litre bench-scale sequencing batch reactors. The sequencing batch reactors were operated concurrently under the same operating conditions. A cycle of 24 hours was adopted during the course of this study. Two different temperature regimes (22°C and 10°C) were employed, and a range of initial BOD5 concentrations was treated. The results showed the occurrence of very high reductions in BOD5 and COD concentrations, and very high removal of ammonia---nitrogen and suspended solids. The average five-day BOD5 reduction was 98% for high influent concentrations, while the reduction for lower influent concentrations was 95%. The average five-day BOD5 concentration for the effluents was less than 100 mg litre−1. Nitrification was pronounced after 40 days of reactor operation. Denitrification occurred when the reactors were fed wastewaters with high BOD5 concentrations, although it was not observed with low influent BOD5 concentrations or at low temperatures (10°C). The overall treatment efficiency remained very high when the reactors were operated under a low temperature regime (10°C).  相似文献   

10.
This study evaluated wood chips and wheat straw as inexpensive and readily available alternatives to more expensive plastic media for denitrification processes in treating aquaculture wastewaters or other high nitrate waters. Nine 3.8-L laboratory scale reactors (40 cm packed height × 10 cm diameter) were used to compare the performance of wood chips, wheat straw, and Kaldnes plastic media in the removal of nitrate from synthetic aquaculture wastewater. These upflow bioreactors were loaded at a constant flow rate and three influent NO3–N concentrations of 50, 120, and 200 mg/L each for at least 4 weeks, in sequence. These experiments showed that both wood chips and wheat straw produced comparable denitrification rates to the Kaldnes plastic media. As much as 99% of nitrate was removed from the wastewater of 200 mg NO3–N/L influent concentration. Pseudo-steady state denitrification rates for 200 mg NO3–N/L influent concentrations averaged (1360 ± 40) g N/(m3 d) for wood chips, (1360 ± 80) g N/(m3 d) for wheat straw, and (1330 ± 70) g N/(m3 d) for Kaldnes media. These values were not the maximum potential of the reactors as nitrate profiles up through the reactors indicated that nitrate reductions in the lower half of the reactors were more than double the averages for the whole reactor. COD consumption per unit of NO3–N removed was highest with the Kaldnes media (3.41–3.95) compared to wood chips (3.34–3.64) and wheat straw (3.26–3.46). Effluent ammonia concentrations were near zero while nitrites were around 2.0 mg NO2–N/L for all reactor types and loading rates. During the denitrification process, alkalinity and pH increased while the oxidation–reduction potential decreased with nitrate removal.

Wood chips and wheat straw lost 16.2% and 37.7% of their masses, respectively, during the 140-day experiment. There were signs of physical degradation that included discoloration and structural transformation. The carbon to nitrogen ratio of the media also decreased. Both wood chips and wheat straw can be used as filter media for biological denitrification, but time limitations for the life of both materials must be considered.  相似文献   


11.
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.  相似文献   

12.
Application of readily-oxidizable organic substrate to laboratory soil-water systems and fish ponds caused anaerobic conditions in bottom soil and water, and concentrations of soluble reactive phosphorus (SRP) increased. Aeration of ponds increased total phosphorus (TP) concentrations by suspending soil particles in the water, but SRP concentrations declined because of increased oxy- genation of bottom water and soil, Alum [Al2(SO4)3·14H2O] treatment of ponds reduced SRP and TP concentrations in ponds, but the low concentration of alum used, 20 mg/L, had little residual effect on phosphorus concentration. Application of agricultural limestone at 0.2 kg/m2 to ponds with soil pH of 5.5 and Ca2+ concentration of 5 mg/L did not affect SRP and TP concentration. Unless pond soils were anaerobic at their surfaces, a condition not acceptable in thermally-unstratified fish ponds, soils released little phosphorus to the water. Strong adsorption of phosphorus by soils in intensive ponds with feeding is beneficial, because removal of phosphorus by aerobic soils is a control on excessive phytoplankton growth. In fertilized ponds, phosphorus must be applied at frequent intervals to replace phosphorus removed from the water by soils.  相似文献   

13.
Excessive dietary phosphorous (P) concentrations in effluents from aquaculture present a major environmental problem. We therefore studied the effect of dietary P and vitamin D3 on P utilization by rainbow trout-fed practical diets and on P concentrations in the soluble, particulate and settleable components of the effluent from fish tanks. Rainbow trout (average weight: 78 g, initial biomass: 13 kg in 0.7 m3 tanks) were fed for 11 weeks, practical diets that varied in total P, available P, and vitamin D3 concentrations. Soluble, particulate (10–200 μm) and settleable (>200 μm) P in the effluent were sampled every 0.5–6 h for 1–3 days in the third and eleventh weeks of the experiment. Trout in all diets more than doubled their weight after 11 weeks. Increasing the concentrations of available dietary P from 0.24% to 0.88% modestly enhanced growth rate. Feed conversion ratio (FCR) and biomass gain per gram P consumed decreased as dietary P concentrations increased. Carcass P, daily P gain, and plasma P concentrations were lower in fish fed with low P diets. Soluble P concentrations in the effluent peaked immediately after and again 4–6 h after feeding, and is a linear function of available dietary P. No soluble P would be produced during consumption of diets containing less than 0.22±0.02% available P. Above this dietary concentration, soluble P would be excreted at 6.9±0.4 mg/day/kg for each 0.1% increase in available dietary P. Particulate P concentrations in the effluent were independent of dietary P concentrations. Settleable, presumably fecal, P concentrations tended to increase with dietary P concentrations. In trout fed with low P (0.24% available P, 0.6% total P) diets, 60% of total dietary P were retained by the fish and the remaining 40% were excreted in the effluent as settleable P (20–30%) and particulate or soluble P (10–20%). In trout fed with high P (0.59–0.88% available P; 0.9–1.2% total P) diets, 30–55% of total dietary P was retained by fish, and the remaining 15–25% appeared in the effluent as settleable P, 20–55% as soluble P, and 5–10% as particulate P. Vitamin D3 did not affect fish growth nor effluent P levels. Physicochemical management of aquaculture effluents should consider the effect of diets on partitioning of effluent P, the peaks of soluble P concentration following feeding, and the contributions of particulate P to total P in the effluent. Increasing our understanding of how dietary P is utilized and is subsequently partitioned in the effluent can contribute significantly towards alleviating this important environmental and industry problem.  相似文献   

14.
The objective of this research was to evaluate the dissolved carbon dioxide stripping efficiency of two types of 1-m tall structured plastic packing (tubular NORPAC and structured block CF-3000 Accu-Pac media) that were placed separately in two full-scale forced-ventilation cascade columns that were located within a coldwater recirculating aquaculture system at the Freshwater Institute. These two structured packing types were selected because they both provide large 4–5 cm void spaces that are either vertically-continuous (e.g. the tubular NORPAC) or an open structure with zigzagging but continuous void spaces (e.g. the blocks of cross-corrugated sheet media), which should reduce the likelihood of plugging with biosolids. Water flow rates were adjusted so that each cascade column was loaded with either 87, 136 and 187 m3/h water flow per m2 of cascade column plan area (i.e. 35, 56 and 76 gpm/ft2). Air:water loading rates of 2.2:1 to 3.4:1, 5.1:1 to 5.6:1, and 9.5:1 to 9.9:1 were produced by setting the water flow rates through each column at 1.62, 2.54 and 3.48 m3/min, respectively, and then measuring the resulting air flow rate through the column under these conditions. As expected, the dissolved carbon dioxide removal efficiencies of both structured packing tested were found to depend on the volumetric air:water loading rate applied. The lowest volumetric air:water loading rate (i.e. 2.2:1 to 3.4:1) resulted in only 21–24% dissolved carbon dioxide removal. However, the dissolved carbon dioxide removal efficiencies rose to 32.4–33.6 and 35.8–37.2% for the medium and high air:water loading rates, i.e. 5.1:1 to 5.6:1 and 9.5:1 to 9.9:1, respectively. A second objective of this research was to determine if either packing would plug with biosolids after long-term operation. At the end of approximately 1 year of operation, both of the plastic packing materials were examined from the top of the packing to determine if potential fouling or plugging problems were apparent. A thin layer of brown biofilm covered both packings, but the biofilm did not appear to threaten water or airflow through the packing. In addition, no large mats of biosolids were visible from the top of either column. However, flooding at the interface of the support screen and the tubular NORPAC was suspected to have reduced air flows measured at the highest hydraulic loading rate tested (i.e. at 187 m3/h per m2), which coincided with the lowest air:water loading rates tested.  相似文献   

15.
Sedimentation and resuspension processes of aquaculture biosolids (non-ingested feed and faeces) are analysed using vertically oscillating grids as a source of turbulence in fluid tanks. An oscillating grid system consists of a container in which a grid is stirred vertically generating a well-known turbulent field that is function of amplitude and frequency of oscillation, distance between grid and measurement point, and mesh spacing of the grid. The grid used in this study had a mesh spacing of 1.2 cm, and was calibrated using different amplitudes (1, 1.5 and 2 cm), frequencies (from 1 to 6 Hz) and distances (2.4, 2.7 and 3 cm). After calibration, the turbulence needed to resuspend biosolids and to maintain them in the water column following different times of consolidation, and with biosolids of different origin, was analysed. It was observed that the turbulence needed to resuspend aquaculture biosolids increased with the time of consolidation. When the turbulence was decreased after a resuspension process, the next sedimentation of biosolids showed a hysteretic behaviour: turbulence needed to resuspend a fixed percent of biosolids from the tank bottom is substantially higher than that needed to maintain the same percentage suspended in the water column. Differences in resuspension behaviour of biosolids originated in different tanks were also observed.

The method provides useful information that can be compared with turbulence generated by fish swimming activity, in order to determine the culture conditions, which can promote self-cleaning conditions in a particular tank.  相似文献   


16.
Acid sulfate soil formation was observed experimentally during leaching of pyritic soil material. Pyritic soil was saturated with distilled water in glass columns and treated under waterlogged and drained conditions. Waterlogged was inundated and had overlying water of 2-cm depth above soil surface. Temporal changes of various chemicals and physical characteristics of the soil and leachates were determined at 10-day leaching intervals. Results showed that strong acidification of soil in drained column but not in waterlogged was due to pyrite (FeS2) oxidation and the consequent production of sulfuric acid (H2SO4). As oxidation progressed, acidification influenced the pH, and increased the solubility of aluminum (Al) and iron (Fe). The loss of potassium (K) and sulfur (S) fractions was also enhanced by acidification. Strong acidic condition in drained columns slightly changed the texture of the soil to more clay, but was not enough to alter the mineral composition of the soil. Periodic leaching was found effective in increasing soil pH, but some essential nutrients were also removed, thus, the need for fertilization scheme during amelioration. In prospective ponds, pyritic soil should be tilled and dried for 2–3 weeks, then flushed and drained repeatedly until pH > 5 is obtained. Repeated lime incorporation should be done in the amelioration until high pH values are obtained. In existing ponds, formation of acid sulfate soil could be avoided by not excessively turning and exposing the pond bottom.  相似文献   

17.
In order to reduce the impact that trout farm effluent can have on receiving water, it imperative to reduce the overall phosphorus (P) loading of these effluents. In response, the United States Environmental Protection Agency (US EPA) is issuing new effluent regulations for aquaculture. Therefore, efficient removal of P from effluent water is becoming increasingly important. The goal of this project was to determine the leaching rate of total and reactive P from trout feces under different water temperatures and water velocities immediately after evacuation. Scatter plots of the P load in the experimental containers over time were created for each fish/fecal sample and regression analysis was used to determine P leaching rates. Results from this study suggest that reactive phosphorus leaching rates are not affected by water velocities between 0.027 and 0.134 m/sec. However, at higher temperatures, reactive P leaches 1.92-mg PO4/hr per g feces faster ( F 1.52= 4.6445, P = 0.0358) than at lower temperatures. Mean reactive phosphorus leaching rates were 2.88 ± 0.704 and 0.96 ± 0.581mg PO4/hr/g feces, for the high and low temperatures, respectively. On the other hand, total P does not appear to be affected by either water velocity or temperature. Mean total P leaching rate is 4.50 ± 1.053 mg PO4/hr per g feces. This study suggests that removal time of feces from the system is critical in reducing the overall P load in effluent.  相似文献   

18.
Closed recirculation systems (CRS) present an alternative for providing organisms to the aquaculture. A CRS with zero water exchange was used in the present study; the CRS consisted of a culture and maturation facility, biofilter system and reservoirs tanks. During two consecutive trials, the CRS efficiency was evaluated by assessing the growth, survival and maturation of juveniles into adults Litopenaeus vannamei (Boone). Throughout the study, water quality parameters (temperature, pH, salinity, NH3, NO2 and NO3) and ion concentration were monitored. Most parameters showed fluctuations without significant differences. However, a decrease in pH was observed during the maturation phase, and an increase in phosphorus was detected, in both the trials, compared with that in initial seawater. Growth and survival for juvenile and pre-adult shrimps presented similar variations without significant differences. Female gonadal maturation and spawning rate were not significantly different between trials. Unfortunately, shrimp eggs underwent lysis 6 h after spawning. These results show that the growth, survival and maturation obtained under CRS conditions are reproducible, and suggest the possibility of using these systems for biosecure shrimp culture, protected against eventual diseases outbreaks. The results of this study also suggest the importance of future studies addressing ion concentration changes in a CRS with zero water exchange.  相似文献   

19.
Nine commercial feeding attractants and stimulants for Litopenaeus vannamei were evaluated by observation of behavioral responses in animals allotted in one Y-maze aquarium apparatus. In the validation phase, fishmeal–Brazilian origin (FMBO); fishmeal–Peruvian origin (FMPO); blood meal (BM), meat and bone meal (MBM), squid meal (SM), fish oil (FO) and fish solubles (FS) were evaluated. There was also a control without stimulatory raw material. The tested materials were included at 3% in neutral gelatin pellets (wet basis). In each behavioral observation, two different ingredients were offered at the same time in equal quantities, being allotted in the end of each chamber's arm. In Phase II after system validation, the following commercial attractants were tested: 80% crude protein (CP) vegetable dried biomass (VDB80), 68% CP vegetable dried biomass + glutamate + betaine (VDB68), complex of amino acids (alanine, valine, glycine, proline, serine, histidine, glutamic acid, tyrosine and betaine) with enzymatically digested bivalve mollusk (CAA), condensed fish soluble protein (CFSP), squid liver meal (SLM), betaine (Bet), dried fish solubles–low biogenic amines (DFSLB), dried fish solubles–high biogenic amines (DFSHB) and whole squid protein hydrolysate (WSPH). Attractants were used at a 3% level wet basis with neutral gelatin, without any additional ingredient source available. The best four commercial attractants from this phase (CAA, CFSP, SLM and WSPH) were compared under 0.5% and 1.0% levels. In Phase I of the study, a higher percentage of choices were observed for FMPO and FMBO. BM and FO were the least chosen ingredients. In Phase II, the worst results were observed for Bet, DFSHB and, mainly, for VDB80 and VDB68. When two-by-two comparisons were performed, results suggested that CFSP and CAA were the best commercial attractants tested. In the last phase, both CFSP and CAA at 1.0% level were significantly more chosen by shrimp than CFSP (0.5%), SLM (0.5 or 1.0%) or WSPH (0.5 or 1.0%). At both 0.5% and 1.0% levels, shrimp spent a similar amount of time feeding on CFSP and CAA. However, only CAA was statistically better than SLM and WSPH together. Further work is required to better elucidate the chemical drivers of chemostimulation for L. vannamei for each one of the attractants tested.  相似文献   

20.
Sieving as an effluent treatment method for aquaculture   总被引：1，自引：0，他引：1  
A new device designed for sieving of fish farm effluent (trademark Triangel Filter TF 2400) was tested in order to prove if such an apparatus may be used instead of the swirl concentrator. The phosphorus reduction was estimated by water sampling and phosphorus budget and by measuring the phosphorus content in flushing water and in settled sludge.

Sieving is a promising and useful method to treat aquaculture effluent, especially in ‘high-tech’ systems (recirculation, warmed water facilities) where high effluent quality and the most effective removal of solids is needed.  相似文献   


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