Foam Fractionator Research Articles

Total Bakteri dan Kelimpahan Vibrio pada Budidaya Udang Vannamei (Litopenaeus vannamei) Sistem Resirkulasi Tertutup dengan Padat Tebar Berbeda

Microbial management is one of the succesful keys on shrimp farming with high density and environtmental friendly culture system. This study was aimed at inversigation on abudance of total bacteria and Vibrio in vannamei shrimp culture using closed recircultion system with different stocking densities. This study used an experimental method with complete randomized design factorial and was performed with closed recirculation system equipped by bio-filters, protein skimmer, and using artificial feed with addition of probiotic. 9 ponds were used for this experiment including 3 control ponds (K) with 200 ind/m2 stocking density, 3 ponds I (P1) and 3 ponds II (P2) with 500 ind/m2 and 750 ind/m2 stocking density, respectively. Those 3 pond with similar stocking density represented as three times of repetition. After 60 days culture period, the average total bacteria and abundance of Vibrio collected from culture water of K, P1, and P2 ponds were 1,2 x 104, 1,6 x 105, and 2,1 x 104 CFU/mL and 1,2 x 103, 2,8 x 103, and 3,7 x 102 CFU/mL. Moreover, at he end of experiment, the average total bacteria and abundance of Vibrio collected from Shrimph body of K, P1, and P2 ponds were 2,7 x 106, 1,6 x 106, and 4,9 x 104 CFU/mL and 2,0 x 103, 1,4 x 103, and 8,5 x 102 CFU/mL. The statistical test of ANOVA was not significant (p> 0,05) between ponds.

A review on the research status and development trend of equipment in water treatment processes of recirculating aquaculture systems

AbstractRecirculating aquaculture systems (RASs) are intensive aquaculture facilities models that depend on diverse water treatment equipment to maintain good water quality and produce safe and healthy high‐quality aquatic products. This article combines the main farming‐mode of water purification recirculating processes with recent cultivation‐mode scientific research and the current development of the recirculating aquaculture industry. Harmful substances are present in aquaculture wastewater due to large quantities of residual particulate matter such as residual feed, faeces and small suspended solid particles, as well as ammonia, nitrite, bacteria and carbon dioxide (CO2), in the water. These harmful substances seriously affect the quality of aquatic products, so water treatment equipment is needed to remove these substances, add oxygen (O2) to the water and adjust the temperature of the water to ensure a high‐quality environment for fish survival. This article reviews the equipment for physical filtration (e.g. solid–liquid separation equipment, microscreen drum filter and foam fractionator) that could remove suspended solids during the water treatment of RASs and the equipment for biological filtration (e.g. fluidized sand biofilter (FSB), moving‐bed biofilm reactor (MBBR) and rotating biological contactor (RBC)) that could remove ammonia nitrogen, nitrite and other hazardous substances from wastewater, as well as equipment for water disinfection and sterilization, O2 addition, CO2 removal and temperature control. Comprehensive analysis and discussion of water treatment efficiency are provided for reference to create efficient high‐end recirculation aquaculture models and increase the precision and intelligence degree of recirculating water treatment technologies in the future.

Comparing biofloc, clear-water, and hybrid nursery systems (Part I): Shrimp (Litopenaeus vannamei) production, water quality, and stable isotope dynamics

Indoor, intensive, nursery-based recirculating aquaculture systems (RAS) can provide high-quality juvenile shrimp for indoor or pond-based production systems in a biosecure manner. However, it is unclear what type of RAS is most appropriate for indoor shrimp nurseries. This study compared three types of RAS nurseries: biofloc (BF), clear-water (CW), and hybrid (HY). Each treatment included four, randomly assigned 160 L (0.35-m2) tanks that were stocked with 3000 post-larvae shrimp m−3. The post-larvae (PL10) shrimp had an initial average weight of 7 ± 0.0 mg and were grown for 48 days. The BF tanks included external settling chambers as the only filtration mechanism. The CW tanks had settling chambers, foam fractionators, and external biofilters to fully clarify the water and process nitrogenous waste. Hybrid tanks included settling chambers, and external biofilters to maintain some suspended solids along with external biofiltration. Overall, the CW treatment had significantly higher dissolved oxygen (DO) and pH levels than the BF and HY systems. The HY treatment had significantly higher DO than the BF treatment. Nitrite concentration was significantly higher in the HY treatment than the CW treatment. Turbidity in the BF treatment was significantly higher than the other treatments. On the final sample date, the BF treatment had significantly higher nitrite and nitrate concentrations than the other treatments. Differences between treatments in terms of shrimp survival, mean harvest weight, specific growth rate, and feed conversion ratio were not significant. The final weight of the shrimp at 48 days for the BF, CW, and HY were 670 mg, 640 mg, and 590 mg respectively. A stable isotope mixing model indicated that, in the BF treatment, 13% of the C and 34% of the N in harvested shrimp tissue may have originated from biofloc material, signifying some nutrient recycling. The nitrification process was more effective with the inclusion of an external biofilter. All three system types appear suitable for RAS shrimp nursery production although consideration should be given to water quality consistency and filtration costs.

Comparing biofloc, clear-water, and hybrid recirculating nursery systems (Part II): Tilapia (Oreochromis niloticus) production and water quality dynamics

Indoor, recirculating aquaculture systems (RAS) can be used to nurse tilapia fry in a biosecure environment to support a variety of production systems; however, it is not understood what type of RAS may be most appropriate for this task. Clear-water and biofloc systems have advantages and disadvantages; hybrid systems combining positive features of both could optimize animal performance and minimize production costs. In this study, four replicate 160-L tanks were randomly assigned to clear-water (CW), biofloc (BF), or hybrid (HY) treatments. CW tanks had a settling chamber, foam fractionator, and external biofilter containing biomedia. BF tanks only had a settling chamber, and HY tanks used a settling chamber and external biofilter. Tilapia (Oreochromis niloticus) were stocked at 55 per tank (305 fish/m3) at 0.17 g average weight. Total Ammonia Nitrogen (TAN) and nitrate were not significantly different between systems. Nitrite was significantly higher in BF compared to CW and HY systems during the last 4 weeks of the study. Turbidity was significantly higher in BF systems versus other treatments. Tilapia in HY systems had significantly higher average weight and specific growth rate compared to BF. Tilapia in BF systems had significantly higher feed conversion ratios and significantly lower harvest biomass versus other treatments. Diminished performance in BF systems likely resulted from inferior water quality conditions. The results indicate that CW or HY systems may be a better choice for tilapia nurseries than chemoautotrophic BF systems due to the short term periods in which nurseries operate and the volitility of nitrification in biofloc systems.

IMPACT OF NURSERY USING DIFFERENT PHYSICAL FILTRATION SYSTEM ON HEMOLYMPH GLUCOSE LEVEL AND SURVIVAL RATE OF SPINY LOBSTER JUVENILE Panulirus homarus

The problems in culture of early juvenile phase of spiny lobster Panulirus homarus is low survival rate of the seed. One of strategies to improve production is using filtration system during nursery of spiny lobster. The aim of this study to evaluate differentation of physical filtration system on responsse stress and survival rate of juvenile P. homarus. Experimental design of this study consisted of four treatments and two replications. The treatments were using flow through system without protein skimmer and filter (K), filtration system with protein skimmer (SK), filtration system with top filter (F) and filtration system with combinations of protein skimmer and top filter (SKF). P. homarus with initial weight 0.18+0.01 g were cultured for 60 days with density 250 lobster/tank. During maintenance, P. homarus were fed trash fish with feeding rate 20% of body weight. Parameters of glucose hemolymph were evaluated to determine stress response. Stress response was determined at day 0, 6, 20 and 60. Parameters of survival rate were determined at the end of experiment. The result showed that the treatment of filtration system with combination of protein skimmer and top filter (SKF) decreased stress responsse by decreasing glucose hemolymph of juvenile P. homarus during maintenance. Survival rate also higher (P<0.05) in treatment SKF (33.2%) than other treatments. It is concluded that SKF was the best physical filtration system for juvenile period of spiny lobster P. homarus Keywords: filtration system, glucose hemolymph, spiny lobster, survival rate

Comparing clear-water RAS and biofloc systems: Shrimp (Litopenaeus vannamei) production, water quality, and biofloc nutritional contributions estimated using stable isotopes

Indoor shrimp aquaculture systems can be used to produce fresh, never-frozen, quality shrimp near metropolitan seafood markets regardless of season and climate. However, questions still remain regarding what type of production system is best suited to maximize indoor production. In this project, two types of systems were compared: clear-water (CW) RAS and biofloc (BF) systems. Three, 1.36m3 tanks were assigned to each of the two treatments; CW tanks had external settling chambers, two foam fractionators, and external biofilters, all operated continuously. BF tanks had settling chambers and one foam fractionator which were operated as needed to control solids accumulation. Shrimp weighing 0.42g were stocked in all tanks at 250m−3 and grown for 55 days. Ammonia and pH levels were significantly (P<0.05) higher in the CW treatment, while nitrite, nitrate, and turbidity were all significantly higher in the BF treatment, although all parameters remained within acceptable ranges for shrimp growth. Shrimp mean harvest weight was significantly higher, biomass (kgm−3) was significantly greater, and FCR was significantly lower in the CW treatment; there were no significant differences in survival between treatments. Isotope levels indicated that shrimp in the BF treatment obtained a portion of the C (18-60%) and N (1-18%) in their tissues from biofloc material; however, this effect did not positively influence production in that treatment. By nearly eliminating solids from the water and using an external biofilter, substantially better water quality was maintained in the CW systems, which may have been a major contributor to the improved shrimp production in that treatment.

Commercial production of tiger puffer (Takifugu rubripes) in winter using a recirculating aquaculture system

Tiger puffer (Takifugu rubripes) is a promising species for aquaculture production because of its high value and limited supply. However, in the north of China, using sea cages to culture this species in winter is hampered by the fact that the seawater temperature is extremely low. Here, a large scale commercial production of tiger puffer has been successfully realized using a recirculating aquaculture system (RAS) from 3 October 2012 to 31 May 2013. The RAS was comprised of nine culture tanks (total water volume 200 m3) and stocked with approximately a total of 14400 fish (initial mean weight 160 g). The tiger puffer was hand-fed at a rate of 0.7% of total body weight per day, and the feed conversion rate was (1.21 ± 0.3) kg kg−1. The recycle water in RAS was treated by a sieve bend screen, a foam fractionator, a submerged biofilter, an UV sterilizer and a submersible aerator. During the whole culture period, an excellent water quality control was achieved in RAS. At the end of this experiment, the survival rate of tiger puffer was more than 98%. The final tank densities averaged 31.2 kg m−3, and the final individual mean weight was 440 g.

The Performance of Continuous Rotifer (Brachionus Plicatilis) Culture System for Ornamental Fish Production

Rotifers are considered as one of the most important prey organisms in the culture of altricial fish larvae. However, high density rotifer culture is often problematic due to water quality problems which results in frequent crashes. In the present study, the performance of a small-scale, continuous system was evaluated for culturing rotifers, Brachionus plicatilis, using concentrated nonviable green algae, Nannochloropsis oculeataas feed in a 160 L tank for a period of 90 days. The system configuration was simple and major components consisted of a protein skimmer and a pure oxygen delivery system. Although egg ratio increased from 3% on day 1 to 21.8% and 39.3% on days 7 and 9, respectively, rotifer growth was slow at start up and resulted in fluctuations in total number of rotifers between days 19-41. Rotifer densities remained < 400 until day 51 but increased at higher rates reaching 900 individuals/mL on day 55, 1,620 on day 60 and 2,127 on day 70. Rotifer density reached a maximum of 2,188 individuals/mL on day 85. Once the rotifer density exceeded 1,500 individuals/mL (day 60), periodical harvesting (a total of 16 harvest events) produced a total of 369,920,000 rotifers corresponding to a daily production of 12,330,667 individuals/day during the next 30 days until the experiment was terminated at day 90. As a result of periodic harvesting, water makeup and continuous protein skimming, total settleable solids and NH3-N levels remained low and ranged between 4-22 mL/L and 0.4-2.2 mg/L, respectively. The authors' findings indicated that this inexpensive culture system can be successfully used for small-scale marine or freshwater ornamental fish production. Further work is required to minimize lag period at start-up and increase the production potential and yield by better management of suspended solids.

Effects of two different ozone doses on total residual oxidants, nitrogen compounds and nitrification rate in seawater recirculating systems for black seabream Acanthopagrus schlegelii (Bleeker)

Ozone was applied to seawater recirculating aquaculture systems (RAS) to measure the effects on water quality and biofilter efficiency. Three replicate experimental systems were used in this study. Each system consisted of four rectangular culture tanks, a sump, two settling chambers, a foam fractionator and a trickling biofilter. The control system (CS) was not ozonated, but Treatment 1 (T 20) and Treatment 2 (T 40) were ozonated with 20 and 40g O3/kg feedday−1, respectively. Three hundred twenty black seabream (mean weight±S.D. of 334.5±1.9g) were stocked into each system, and cultured for the entire 44-day study period. During this period, total residual oxidants (TRO), nitrogen compounds (Total-ammonia–N, TAN; nitrite–N, NO2–N and nitrate–N, NO3–N) were measured, and nitrification efficiencies of the trickling biofilters were calculated for each system.Generally, the application of ozone to the seawater systems reduced TAN and NO2–N concentrations in the culture tanks of both treatments. However, the nitrification rate of the biofilter in the T 40 and the CS systems was about 50% lower than the rate of the biofilter in the T 20 system. Therefore, the use of a moderate dose of ozone (20g O3/kg feedday−1) appears to enhance nitrification, possibly through the reduction of dissolved organic matter that may interfere with bacterial activity.However, application of ozone at 40g O3/kg feedday−1 appears to depress microbial activity associated with biofiltration and nitrogen removal efficiency, perhaps through toxicity of associated compounds or directly through residual oxidants. Based on the results of this study, continuous ozonation should not exceed 20g ozone/kg feed (mean TRO 0.15mg/L) in a seawater RAS to avoid negatively affecting the nitrification efficiency of the bio-filters.

Effect of copper on the growth of shrimps Litopenaeus vannamei: water parameters and copper budget in a recirculating system

Shrimps (Litopenaeus vannamei) were intensively cultured in a recirculating aquaculture system for 98 days to investigate effects of 0.3 mg/L Cu on its performance, Cu budget, and Cu distribution. Shrimps in Cu-treated systems had greater mean final weight (11.10 vs 10.50 g), body length (107.23 vs 106.42 mm), survival rate (67.80% vs 66.40%), and yield (6.42 vs 5.99 kg/m3), and lower feed conversion ratio (1.20 vs 1.29) than those in control systems but the differences were not significant. Vibrio numbers remained stable (104–106 colony forming units/mL) in the rearing tanks of both control and treated systems. Total ammonium-N, nitrite-N, nitrate-N, pH, chemical oxygen demand, 5-day carbonaceous biochemical oxygen demand, and total suspended solids were similar in controls and treatments. Dissolved Cu concentration in the treated systems decreased from 0.284 to 0.089 mg/L while in the control systems it increased from 0.006 2 to 0.018 mg/L. The main sources of Cu in the treated systems were the artificially added component (75.7% of total input), shrimp feed (21.0%), water (2.06%), and shrimp biomass (1.22%). The major outputs of Cu occurred via the mechanical filter (41.7%), water renewal (15.6%), and draining of the sediment trap (15.1%). The foam fractionator removed only 0.69% of total Cu input. Harvested shrimp biomass accounted for 11.68% of Cu input. The Cu concentration of shrimps in the Cu-treated systems (30.70 mg/kg wet weight) was significantly higher than that in control systems (22.02 mg/kg). Both were below the maximum permissible concentration (50 mg/kg) for Cu in seafood for human consumption in China. Therefore, recirculating systems can be used for commercial on-growing of Litopenaeus vannamei without loss of shrimp quality, even in water polluted by 0.30 mg/L Cu. The mechanical filter is the main route for Cu removal.

Intensive nursery production of the Pacific white shrimp Litopenaeus vannamei using two commercial feeds with high and low protein content in a biofloc-dominated system

The efficiency of shrimp production in limited exchange systems can be improved by optimizing the protein content of the feed. Therefore, a 62-d nursery study was conducted with 10-day-old Litopenaeus vannamei postlarvae stocked (5000PL10m−3) in four 40m3 raceways to evaluate the effect of high (40%) and low (30%) crude-protein (HP40 and LP30, respectively) diets and molasses supplementation on selected water quality indicators and shrimp performance under limited water exchange. Each raceway was equipped with a real-time dissolved oxygen monitoring system and a foam fractionator to control particulate matter. The level of molasses used in this study was effective in preventing significant ammonia accumulation in the culture medium. However, these supplementation levels were not effective in preventing nitrite accumulation. The HP40 treatment had significantly higher nitrite, nitrate and phosphate concentrations than the LP30 treatment. Shrimp mean final weight (0.94 vs. 1.03g) and specific growth rate (SGR) (11.03 vs. 11.19% day−1) were significantly different between treatments (P<0.05) LP30 and HP40, respectively, while mean survival (∼82% vs. 84%) and protein efficiency ratio (PER) (3.89 vs. 3.28) were not (P>0.05). The data suggest that substituting high-protein (40%) with low-protein (30%) feed in the nursery phase in a biofloc dominated system operated with minimal discharge may provide an alternative to improve shrimp biofloc technology, through improved water quality, cheaper (lower protein) feed and reduced environmental impact.

Molecular Analysis of Bacterial Communities and Detection of Potential Pathogens in a Recirculating Aquaculture System for Scophthalmus maximus and Solea senegalensis

The present study combined a DGGE and barcoded 16S rRNA pyrosequencing approach to assess bacterial composition in the water of a recirculating aquaculture system (RAS) with a shallow raceway system (SRS) for turbot (Scophthalmus maximus) and sole (Solea senegalensis). Barcoded pyrosequencing results were also used to determine the potential pathogen load in the RAS studied. Samples were collected from the water supply pipeline (Sup), fish production tanks (Pro), sedimentation filter (Sed), biofilter tank (Bio), and protein skimmer (Ozo; also used as an ozone reaction chamber) of twin RAS operating in parallel (one for each fish species). Our results revealed pronounced differences in bacterial community composition between turbot and sole RAS, suggesting that in the systems studied there is a strong species-specific effect on water bacterial communities. Proteobacteria was the most abundant phylum in the water supply and all RAS compartments. Other important taxonomic groups included the phylum Bacteriodetes. The saltwater supplied displayed a markedly lower richness and appeared to have very little influence on bacterial composition. The following potentially pathogenic species were detected: Photobacterium damselae in turbot (all compartments), Tenacibaculum discolor in turbot and sole (all compartments), Tenacibaculum soleae in turbot (all compartments) and sole (Pro, Sed and Bio), and Serratia marcescens in turbot (Sup, Sed, Bio and Ozo) and sole (only Sed) RAS. Despite the presence of these pathogens, no symptomatic fish were observed. Although we were able to identify potential pathogens, this approach should be employed with caution when monitoring aquaculture systems, as the required phylogenetic resolution for reliable identification of pathogens may not always be possible to achieve when employing 16S rRNA gene fragments.

Culture of yellowtail kingfish (Seriola lalandi) in a marine recirculating aquaculture system (RAS) with artificial seawater

The development of new species is a high priority for the diversification of the Chilean aquaculture sector. The yellowtail kingfish (Seriola lalandi) is a promising candidate for commercial production in recirculating aquaculture systems (RAS). This paper presents data on the culture of yellowtail kingfish in a marine RAS working for 488 days using artificial sea water. Growth performance, feed conversion, feeding rate, condition factor and mortality were determined for fish having an average initial weight (±S.D.) of 0.7±0.2g up to a final average weight of 2006±339.0g. The RAS configuration (drum filter, protein skimmer with ozone, biological nitrification and denitrification, carbon dioxide removal and oxygenation) showed performance stability under the conditions assayed (low water renewal rate). Total ammonia nitrogen and nitrite-nitrogen concentration averaged 0.74±0.42mg/L and 0.21±0.24mg/L respectively. After installation, the denitrification reactor kept nitrate-nitrogen concentrations below 40mg/L. Nitrate-nitrogen was totally reduced at oxidation reduction potential values between −150 and −250mV. Water temperature averaged 22.6±1.4°C and oxygen was maintained close to saturation levels. Carbon dioxide concentration was in average 8.3±2.47mg/L and pH 7.5±0.1. Water renewal rate was 0.45% of the total system volume per day. The system proved the capability to maintain optimal water quality and secured animal welfare.

Design and evaluation of a commercial recirculating system for half-smooth tongue sole (Cynoglossus semilaevis) production

A recirculating aquaculture system was designed for producing half-smooth tongue sole (Cynoglossus semilaevis). The recirculating system included twenty-eight 40-m3 circular culture tanks. The bottom discharge from the culture tanks was treated by passage across a bowed screen, and then water was pumped through a foam fractionator and a series of three submerged biofilters which contained plastic media, BIO-BLOK® element, and porous plastic media, respectively. Water then was disinfected with UV irradiation and supplied with pure oxygen before flowing back to the culture tanks. The system was stocked with 33,073 fish (mean weight 305±57g) in March 2009 and operated with greater than 95% water reuse. At the maximum feeding rate, the cumulative feed burden and loop strength were 7.25kg feed/m3 of water and 11.8mg/l, respectively. Over 8 months, fish survival rate was more than 97%. Fish were harvested from the system in October 2009 at a mean weight of 1246±166g, with a specific growth rate (SGR) through this time of 1.2% body weight per day and feed conversion ratio of 1.1. The system maintained water quality appropriate for the fish, with mean temperature of 19.7°C, DO of 6.7mg/l, pH of 7.37, un-ionized ammonia of 0.012mg/l, and nitrite of 0.044mg/l. Approximately 99% of heterotrophic bacteria and coliform bacteria were inactivated by UV irradiation. Power usages per cubic meter water and per kg of production were 0.11kW and 6.6kW, respectively. Our results demonstrated the utility of recirculating aquaculture systems for producing half-smooth tongue sole. We suggest that regular backwashing of submerged biofilters may raise production capacity and allow use of biofilters with fewer stages.

Spectroscopic studies of dye-surfactant interactions with the co-existence of heavy metal ions for foam fractionation

The interaction between a cationic dye Methylene Blue (MB) and an anionic surfactant sodium dodecyl sulfate (SDS) with the presence of Cd2+ was investigated spectrophotometrically in a certain concentration range. The spectrophotometric measurements of dye-metal ion-surfactant system were carried out. The results indicated that the SDS concentration had a significant influence on the dye spectrum, while the addition of Cd2+ hardly caused change of the maximum value of absorbance. According to this observation, we concluded that electrostatic and hydrophobic interaction between dye and surfactant occurred up to a certain level, and the homo-ions Cd2+ almost exerted no effect on the dye-surfactant complexation, establishing a theoretical foundation for simultaneous removal of organic dye and heavy metal using foam fractionation. Meanwhile, the effects of their interaction on foam performance were investigated. The results showed that the addition of Cd2+ favored the tendency to ameliorate foam properties just contrary to MB. The feasibility of foam separation for dye and heavy metal removal from simulated wastewater was also confirmed using a continuous foam fractionator. In the simultaneous removal process, with the initial SDS concentration ranging from 0.5 to 5.0 mmol/L, the maximum removal efficiencies of MB and Cd2+ were obtained as 99.69% and 99.61%, respectively. The enrichment ratios were reduced from 24.34 to 7.65 for MB and from 22.01 to 3.35 for Cd2+.

Effects of Protein Skimming on Water Quality, Bacterial Abundance and Abalone Growth in Land Based Recirculating Aquaculture Systems

Recirculating aquaculture systems can reduce many challenges associated with open culture systems but maintaining suitable water quality in recirculating system is difficult. Protein skimmer removes organic matter from the water before it breaks down into nitrogenous waste. Therefore, the aim of this study was to evaluate the effects of protein skimming on water quality, bacterial abundance and abalone growth in recirculating aquaculture system. Two recirculating systems utilizing artificial seawater were housed in an air-conditioned, insulated recycle frozen container (4.3×1.9×1.9 m) to maintain optimum water temperature (19.2  0.80C) for abalone growth. Each system consisted of two biofilters (100 and 200 L) and two abalone culture tanks (each 200 L) containing three plastic baskets (each 50 × 34 × 6 cm, with 12 mm mesh). One culture system incorporated a protein skimmer. Over an experimental period of 87 days, protein skimming resulted in significantly better water quality, heterotrophic bacterial abundance and abalone growth. Results indicate recirculating abalone culture systems with protein skimmer housed in an air-conditioned, insulated recycle frozen container may provide a viable alternative to current land-based, flow-through systems. More research is needed to further increase the efficiency of this system.

Effect of Different Filter Methods on Seawater Quality at a Marine Scallop Hatchery

The effect of using two different filtering methods in the main seawater inlet to a scallop (Pecten maximus) hatchery in Norway was tested. Seawater was filtered through active filter media (AFM) and a protein skimmer, or through a drum filter and a protein skimmer. Seawater quality was characterized and tested on algal growth rate, egg development and larval activity. Tests were performed under winter and spring conditions (March, April and May 2009). Both seawater treatments reduced the dissolved organic carbon concentrations in the inlet seawater. The total bacterial number was stable in both seawater treatments, except for an increase in the drum filter in March. The bacterial community showed seasonal development: Actinobacteria and Alphaproteobacteria dominated in March, while Gammaproteobacteria dominated in April and May. In a cluster analysis, samples from both seawater treatments showed high similarity on similar sampling dates. Vibrio spp. occurred, but was never observed in seawater coming from the skimmer after the drum filter. This sampling point was often clustered as most similar to the incoming seawater. The fraction of scallop eggs that developed into veliger larvae increased from 10% to 50% during the sampling period, and no significant differences were found between the two seawater treatments. The fraction of 8 day old active larvae was lowest in March, in experiments with both undiluted and diluted (1:10, 1:100) seawater from both treatments. No significant difference in activity was found between the treatments, except for undiluted (April) and 100-fold dilution (April and May) from the drum filter, when the larval activity was significantly higher. The effect of both seawater treatments was tested by growing the diatom Chaetoceros muelleri in small volumes for 4-5 days. Daily growth rates (μ) varied between 0.75 and 1.15, and were highest in May. No significant difference in cell concentration was found between the treatments. The results showed that the skimmer attached to the drum filter had the best performance overall in reducing dissolved organic carbon and potentially lethal bacteria. These findings have important implications for hatchery seawater management protocols.

Ozone Application in Recirculating Aquaculture System: An Overview

In recirculating aquaculture systems (RAS), particulates (including feces, uneaten feed, bacteria, and algae) can cause several problems, in that they may harbor pathogens, can physically irritate the fish, and upon decomposition, release ammonia and consume oxygen. Mechanical filters, foam fractionators, and other engineered devices are used to remove particles quickly from aquaculture systems, in order to improve fish health and decrease the load on biofilters and oxygenators. Ozone is used in RAS as a disinfectant, to remove organic carbon, and also to remove turbidity, algae, color, odor and taste. Ozone can effectively inactivate a range of bacterial, viral, fungal and protozoan fish pathogens. But the effectiveness of ozone treatment depends on ozone concentration, length of ozone exposure (contact time), pathogen loads and levels of organic matter. In spite of ozone is a very effective oxidizing agent, higher ozone concentrations are a risk to cultured fish stocks causing gross tissue damage and stock mortalities, and also are a risk to bacterial films on the biofilter.

Nitrogen stable isotopes in recirculating aquaculture for super-intensive shrimp production: Tracing the effects of water filtration on microbial nitrogen cycling

To understand how filtration affected microbial community nitrogen (N) cycling, natural abundance stable isotope ratios of suspended particles and nitrate (NO3−) were measured in recirculating aquaculture systems (RAS) for the super-intensive culture (425shrimpm−2) of Pacific white shrimp, Litopenaeus vannamei. Samples were collected throughout a trial during which triplicate RAS were equipped with either a foam fractionator (FF) or a propeller-washed bead filter (BF) to determine solids removal and inorganic N cycling efficacy of each filtration technique. Shrimp performance was unaffected by filtration technique. The time course of DIN concentration was consistent with rapid full nitrification (NH4+ to NO2− to NO3−) in the BF treatment. Persistent, elevated NO2− suggested a slower onset of NO2− oxidation in the FF treatment. However, NO3− began to accumulate at approximately the same time in both treatments and NO3− accumulated more rapidly in the FF treatment even though feed N input to the FF treatment was slightly lower than in the BF treatment. Consistently depleted δ15N–NO3− in the FF treatment illustrated isotopic fractionation of the NH4+ pool attributable to NH4+ oxidation. After an initial depletion, δ15N–NO3− in the BF treatment remained significantly enriched relative to the FF treatment, consistent with isotopic fractionation due to denitrification where the filtration mechanism promoted sub-oxic conditions. The latter is supported by significantly lower NO3− and N budget analyses which indicate the potential for N loss. Together these results suggest that, despite identical inocula, the microbial community responded differently to the filtration technique and as a result natural abundance isotopes revealed distinct dominant N cycle pathways.

Effects of two different ozone doses on seawater recirculating systems for black sea bream Acanthopagrus schlegeli (Bleeker): Removal of solids and bacteria by foam fractionation

Foam fractionators, with and without additional ozonation, were evaluated for their effect on solids removal (suspended solids, SS; volatile suspended solids, VSS; dissolved organic carbon, DOC), particle size distribution of the foam in seawater recirculating systems during a 44-day experimental period. The effect of ozone on heterotrophic bacteria was also quantified in the entire system. Three separate but identical recirculating systems (4.5m3 system volume) with foam fractionators (300mm in diameter, 3m in height) were used in this study. One system (Control: CS) did not receive ozone, while the other two systems were ozonated at a rate of either 20g ozone/day (T 20) or 40g ozone/day (T 40) per kg of feed applied, respectively. A total of 107kg of black sea bream Acanthopagrus schlegeli (Bleeker) with an average weight of 334.5g was stocked into each system. Daily feeding rate was 1% of total body weight. The solids enrichment factor (EF=Cc/Ci, where Cc=concentration in foam condensate, Ci=concentration in inlet water) in T 40 was 10 times more dilute than the factors in CS and T 20. However, due to the higher volume of the foam (>10 times) in T 40, the removal rates of SS, VSS and DOC were the highest in T 40, but were not significantly different from T 20 (P>0.05). The mean particle sizes at the 90% cumulative removal point decreased with ozonation, 71.2±15.9, 57.9±10.2 and 48.0±10.2μm in CS, T 20 and T 40, respectively. The overall mean particle diameter of solids in the foam decreased as ozonation increased, with values of 29.4±4.4, 23.9±3.8 and 20.5±3.7μm in CS, T 20 and T 40. Numbers of heterotrophic bacteria in the inlet were 6.21±4.93×105CFU/mL, 0.29±0.19×105CFU/mL and 0.30±0.29×105CFU/mL in CS, T 20 and T 40, declining sharply with the addition of ozonation. As the number of the bacteria in the inlet decreased, the bacteria in the foam and the removal rate greatly decreased with increasing ozonation. However, EFs in T 20 (76.4) and T 40 (14.5) were higher than that in CS (12.2), and the T 20 showed significantly higher EF (P<0.05). Therefore, based on the EF, ozonation improved the removal efficiency of heterotrophic bacteria, even at the lowest concentration.