Foam Fractionator Research Articles

Virtual Sensing of Nitrite: A Novel Control for Safe Denitrification in Recirculating Aquaculture Systems (RASs)

Recirculating aquaculture system (RAS) technology is seen worldwide as a solution for sustainable fish production. However, there are still deficiencies in the process technology imperiling consistent operation and thus economic results. Drawbacks are linked to essential processes of the water treatment systems such as denitrification. Nitrogenous waste needs to be removed from RAS process water to maintain an adequate production environment for fish and to mitigate the environmental impact of discharged process water. At present, denitrification lacks reliable process control, especially regarding the organic carbon feed to heterotrophic denitrification processes. An investigation into heterotrophic denitrification in an experimental RAS resulted in the discovery of a virtual sensor based on measurements of the oxidation reduction potential (ORP). The virtual sensor responds to an insufficient carbon feed to denitrification. It is based on the oxidation of nitrite in an ozone-enhanced foam flotation installed downstream of the denitrification. The sensor essentially delivers a binary signal denoting either a complete or an incomplete denitrification process. The virtual sensor can be used for reliably controlling heterotrophic denitrification. It requires an upgraded process chain employing ozone-enhanced foam flotation (protein skimmer) downstream of the denitrification. However, the virtual sensor does not require any additional instrumentation.

Study on recirculating aquaculture system (RAS) in organic fish production

Abstract The growth of conventional aquaculture has created environmental issues due to excessive feeding, low dissolved oxygen level etc into the water body. Organic aquaculture is a recent development as a solution to these issues. It is a clean alternative to reduce pollution and to produce safer consumable food. In the past few decades, recirculating aquaculture systems (RAS) were introduced to maintain pond water quality through lesser water exchange, by focusing on water reuse after treatment. In this study, the technical viability of RAS was analyzed for introduction in organic aquaculture systems. Indian major carps (IMCs) were cultured through conventional methods in the three tanks of conventional system, while the same species was grown organically in another three tanks in organic system. The stocking density and physical conditions were kept same for both cultured systems. The RAS consisted of fish culture tank with an average volume of each tank was 165 m3, a screen filter, foam fractionator and trickling filter. The various water quality parameters, i.e., solid size distribution in water, and removal efficiencies in biological treatment of both systems were compared. The present study, particle size distribution of solids in water body was measured by filtration, followed by weighing of dry residue solids. Pore sizes of 1000μ, 100μ, 20μ and 3μ were employed for filtration. For organic tanks, a majority of solids are of size between 1 mm and 100 μm. The larger sized particles (> 30 μm) constitute nearly 70 % of the solids and the trait differs from the generalized conclusions of that a major part of sediments will be of sizes less than 20 μm. For the conventional tanks, majority of solids are of size between 3 mm and 20 μm and TAN shows higher removal efficiencies for effluents from organic system rather than conventional system. The results showed that organic aquaculture causes lesser pollution load per weight of fish. The particle size distribution of organic water was better compatible to screening and sedimentation than conventional water. Also the filtration efficiencies in nitrifying trickling filters of both water bodies were comparable, with that of organic water slightly on the higher side. Thus recirculating water treatment systems are introduced in organic aquaculture.

Fine‐solids removal by foam fractionation in a low‐salinity marine recirculating aquaculture system (RAS)

AbstractObjectiveWe sought to evaluate several methods of operation of a foam fractionator for fine‐solids removal (organic matter < 55 μm) in a commercial‐scale, low‐salinity (11–13‰) recirculating aquaculture system (RAS) for marine finfish production.MethodsThe total suspended solids (TSS) concentrations of the RAS microscreen drum filter inflow and outflow and the foam fractionator outflow were obtained under various foam fractionator operating conditions. The outflow TSS concentration of the drum filter also served as the inflow TSS concentration for the foam fractionator. Sample collection for TSS determination was divided into two categories: particles greater than 55 μm and particles less than 55 μm. The difference between inflow and outflow TSS concentrations was used to determine the removal percentage for each particle class of each unit. Additionally, the volume of foammate produced under operating conditions by the fractionator and the amount of solids contained within the foammate were quantified. Flow through the foam fractionator was also obtained to determine the amount of solids removed per volume of influent water treated.ResultThe influent TSS concentration for the seven different operating conditions evaluated ranged from 4.8 to 6.3 mg/L, with the percentage of particles less than 55 μm ranging from 69.75% to as high as 86.1%. The drum filter removed over 90% of the particles larger than 55 μm and removed 8–26% of the particles smaller than 55 μm. No difference was observed in the overall removal efficiency of the drum filter, which ranged from 19% to 44%. There was no significant difference in the foam fractionator overall removal efficiency, which ranged from 6.5% to 38.5%. Operating the foam fractionator at a high water head height (HHH) with the submersible aspirating impeller provided the greatest removal percentage of particles less than 55 μm (26.9%). However, at the HHH, only half the amount of solids was removed compared to using a Venturi injector with ozone, but energy use was roughly 26% greater.ConclusionThe foam fractionator was operated at the HHH, about 0.31 m higher than the low water head height, for production operation. Additionally, Venturi injection of ozone provided the greatest removal of solids for the volume of influent water treated over a 12‐h operational period. The submersible aspirating impeller showed potential for low‐cost use with reasonable solids removal and warrants further evaluation.

Effects of Protein Skimmer Inclusion in an Integrated Aquaponic System Between the Red Tilapia Hybrid (Florida strain) and Mint (Mentha Spicata)

Effects of Protein Skimmer Inclusion in an Integrated Aquaponic System Between the Red Tilapia Hybrid (Florida strain) and Mint (Mentha Spicata)

Evaluating protein skimmer performance in a commercial seawater recirculating aquaculture system (RAS)

Combining protein skimming with ozone (O3) is a common method for removing microparticles in recirculating aquaculture systems (RAS). Nevertheless, there is a limited number of studies that have validated protein skimming's performance at a commercial scale. Additionally, variations in protein skimmer designs and operational variables may yield different performance outcomes. In the present study, the performance of two types of full-scale protein skimmer (S1 and S2) were compared and evaluated under two levels of hydraulic retention time (HRT) (1.8 and 2.2 min) and three levels of O3 doses (0, 7, and 14 g O3/kg feed) in a commercial seawater RAS facility. Samples from the inlet and outlet of the protein skimmers were collected at each combination of operational variables. They were analysed for several relevant water quality parameters to quantify the treatment efficiency. O3 dose significantly improved water quality and reduced the numbers of microparticles and bacterial activity in a single pass. Besides that, doses as high as 14 g O3/kg feed significantly increased total residual oxidant (TRO) concentration. Additionally, an increase in HRT exerted a moderate effect on removing microparticles and a strong effect on redox potential (ORP) and TRO. Finally, the type of protein skimmer only affected the ORP, causing no significant changes to other water quality metrics. The correlations between the investigated water quality parameters defined a clear pattern of the ongoing processes and particle characteristics. Overall, the results demonstrated that protein skimming combined with carefully selected O3 doses can improve general water quality and control critical factors such as bacterial activity and microparticles under commercial operations.

Water level control of small-scale recirculating aquaculture system with protein skimmer using fuzzy logic controller

The recirculating aquaculture system (RAS) is a land-based aquaculture facility, either open-air or indoors, that minimizes water consumption by filtering, adapting, and reusing water. Solid organic matter from fish waste and food waste directly becomes waste that needs to be eliminated because it is a source of increasing total ammonia nitrogen (TAN), total suspended solids (TSS), total dissolved solids (TDS), and also has an impact on reducing dissolved oxygen (DO). RAS requires a water level control system so the fish tank does not experience water shortages or floods, disrupting the aquatic aquaculture ecosystem. In this study, small-scale RAS is modeled using a 3-coupled tanks system approach with a tank configuration that follows the most straightforward RAS water recirculation process (fish tank, mechanic filter, biofilter). Clean water from the reservoir flows into the fish tank through a protein skimmer. This study applies the fuzzy logic controller (FLC) to control the water level in the protein skimmer and biofilter tanks by controlling the position of several valves where the placement positions of the valves have been determined according to system requirements. The study results show that the tuned single-input FLC has the best average output response characteristics with t<sub>s</sub>=50, h<sub>1ss</sub>=49.98, e<sub>ss</sub>=0.02 in protein skimmer and t<sub>s</sub>=4700, h<sub>1ss</sub>=39.75, e<sub>ss</sub>=0.25 in the tank system.

Life support systems and aquatic communities in public aquariums

The Pangandaran Integrated Aquarium and Marine Research Institute (PIAMARI) was developed in Pangandaran, and is equipped with public aquarium facilities. The Main Aquarium is an oceanarium in the form of a box, with a volume of 1.238 million liters, and accommodates various marine biota. This paper aims to provide an overview of the life support system used and the aquatic communities in the Main Aquarium. An inventory of principal components and equipment, the composition of biota, plankton, and ectoparasites was conducted in the oceanarium. The Main Aquarium is supported by filtration using a sand filter, protein skimmer, and an ozone generator. Water quality is maintained using the filtration combined with partial water changes. There are nine species of fish, including sharks and rays, and two species of turtles that are kept in the oceanarium, where most of the collections are omnivores, with IUCN LC conservation status and the rest NT to CR. Seven plankton genera were identified in the oceanarium (H’:1.78 and E: 0.90). There was Cryptocaryon ectoparasite infestation on the gills and skin of Trachinotus blochii with open lesions. Fish collections show different behavior and consume the fresh and artificial feed. Apart from being an edu-tourism facility, the oceanarium can act as a place for living and ex-situ culture for endangered marine biota.

Implementation of Complex Life Support System for Reef Fish Communities in Cylindrical Oceanariums

The schooling aquarium is cylindrical public oceanarium facilities with 137,000 l volume at PIAMARI Aquarium, Pangandaran. There are not many discussions related to oceanariums in Indonesia and this paper describes the live support system design, biota communities, and management of fish keeping in a oceanarium. Inventarisation of fish species composition, plankton, ectoparasites, and diseases was conducted in this oceanarium, The Oceanarium uses artificial lighting and a recirculation system with a sump equipped with physical, biological, protein skimmers, and ozone generators. Partial water change is applied to maintain the water quality. This oceanarium is a place for 16 fish species types of omnivores, planktivores, and herbivorous originate from Pangandaran waters and belong to IUCN LC conservation status. The fish is well adapted to the oceanarium environment, and each species has different behaviors.. Ten genus of plankton were identified in the oceanarium with diversity belonging to the medium category and become the highest compared to other oceanariums in the PIAMARI environment. Trichodesmium sp. was the highest abundance of plankton genus in the oceanarium. There is a low parasite infestation of Neobenedia sp. in 3 fish species from 2 families (Chaetodontidae and Siganidae). The introduction of coral in the schooling aquarium can be considered by increasing the biological filtration of the sump.

Removal of dissolved organic matter from the woodchip bioreactor start-up by foam fractionation.

Denitrifying woodchip bioreactors are passive, low-tech systems primarily designed to remove nitrate from shallow ground waters as well as point source discharges. Despite their capacity to achieve constant nitrate removal over several years, natural aquatic environments may be affected by the leaching of dissolved organic matter (DOM) from fresh woodchips during start-up. Simple on-site measures might reduce the woodchip leachate during start-up and thus add to the overall environmental sustainability of woodchip bioreactor installations. The aim of the study was to investigate whether foam fractionators could provide an effective solution. Water was flowed through fresh laboratory-scale woodchip bioreactors and recirculated through foam fractionators for 11 days. The bioreactors removed nitrate but increased phosphate and ammonia, which were not effectively removed via foam fractionation. However, foam fractionation did remove 37.8 ± 4.7% of the dissolved chemical oxygen demand (CODdiss) leached during the first 11 days of operation. Fluorescence spectroscopy revealed that the DOM composition differed between the foam and water, where the foam fraction contained higher amounts of DOM associated with the highest bioavailability and hence the greatest potential environmental impact. Optimised foam fractionators could therefore help to reduce the environmental impact of DOM leachate from woodchip bioreactors during start-up.

Dye isolation in a foam fractionation column: Optimization of process parameters

The technique of foam fractionation has already been well received in the field of isolation of proteins using a suitable surfactant. The lower operating cost also makes this technique eligible for treating various wastewater streams. In view of this, methylene blue dye was separated and recovered from its solution by employing sodium dodecyl benzene sulfonate as a collector in a foam fractionator operated in a semi-continuous manner. The separation characteristics were accessed at varying aeration rates, dye concentrations and liquid loadings. Prior to this, the values of other operating variables such as operation time, concentration of the surfactant and solution initial pH were fixed. Subsequently, in order to attain maximum removal fraction and enrichment ratio, individually, Taguchi methodology yielded the optimum values of operating variables, which are crucial for the optimal operation of any foam fractionator. The results revealed implementation of foam fractionation technique in isolating methylene blue dye from dyeing wastewater to be fairly good.

Foam fractionation and ozonation in freshwater recirculation aquaculture systems

Foam fractionation is often considered an ineffective way of removing organic matter from freshwater due to the low surface tension of the water. There is, however, a lack of studies testing foam fractionation efficiency in replicated freshwater recirculating aquaculture systems (RAS). Foam fractionation can be applied with or without ozone. Ozone is a strong oxidiser previously shown to improve water quality and protein skimmer efficiency. To test the efficiency of foam fractionation and ozonation (20 g O3 kg-1 feed) separately and in combination in freshwater RAS, a two-by-two factorial trial was conducted with each main factor at two levels (applied or not applied). Each treatment combination was carried out in triplicates using 12 replicated pilot scale RAS stocked with juvenile rainbow trout (Oncorhynchus mykiss) and operated at a feed loading of 1.66 kg feed m-3 make-up water. The trial lasted 8 weeks and samples were obtained once a week. Ozone applied by itself significantly reduced the number of particles (83%), bacterial activity (48%) and particulate BOD5 (5-days biochemical oxygen demand; 54%), and increased ultra violet transmittance (UVT; 43%) compared to the untreated control group. Foam fractionation by itself lead to significant reductions in particle numbers and volume (58% and 62%, respectively), turbidity (62%), bacterial activity (54%) and total BOD5 (51%). A combination of both treatments resulted in a significant additional improvement of important water quality variables, including a 75% reduction in total BOD5, 79% reduction in turbidity, 89% reduction in particle numbers and 90% reduction in bacterial activity compared to the control. The removal efficiencies were within the same range as those observed in previous studies conducted with foam fractionators in saltwater systems (with or without ozone), corroborating that foam fractionation may become a useful tool for controlling organic matter build-up and bacterial loads in freshwater RAS.

Hydrogen peroxide oxygenation and disinfection capacity in recirculating aquaculture systems

Hydrogen peroxide (H2O2) treatment is an alternative for disinfection in aquaculture, which may be advantageous as it dissociates and disinfects while increasing water oxygen concentration. Yet, accurate dosing remains undeveloped in Recirculating Aquaculture Systems (RAS). Dosage requirements can depend on organic burden, stocking density, feeding frequency, salinity, temperature and biofilter performance. The present case study investigated the dual effect of H2O2 application for oxygen enrichment and disinfection when continuously applied to a RAS rearing European seabass. H2O2 addition equivalent to 2.4 and 15.8 H2O2 mg L−1 were applied for 4 h per day in three 5-days experiments. H2O2 was injected at the inlet of protein skimmer and/or the rearing tanks in or without combination with traditional disinfection methods. Water microbial load and oxygen saturation were determined, along with stress markers glucose and cortisol in blood plasma of fish. Doses of 15.8 mg L−1 H2O2 steadily increased oxygen levels in holding tank water from ∼50 % to over 100 % saturation while reducing microbial load (from 604.4 CFU ml−1 in the rearing tanks before dosing to 159.8 CFU ml−1 after application), achieving suitable conditions for commercial fish densities in RAS. The doses used had negligible impact on biofilter performance and did not affect the fish in terms of stress. Overall results indicate H2O2 is effective for disinfection and oxygenation of RAS systems when applied at appropriate dosage and we recommend the protein skimmer as the safest position in order to protect the bacterial community of the biofilters and the reared fish.

The effects of different solids and biological filters in intensive pacific white shrimp (Litopenaeus vannamei) production systems

Biofloc systems rely on suspended solids in the water to house microbes that can remove or cycle nitrogenous wastes; however, nitrogen cycling can be inconsistent. In contrast, external biofilters are used in many recirculating systems to provide a more consistent environment for microbes to process nitrogen. Regardless of the biofiltration approach, solids levels must be controlled to prevent issues in shrimp such as gill fouling, low dissolved oxygen levels, and other negative impacts. The purpose of this study was to examine the effects of settling chambers versus foam fractionators for solids filtration and to compare external biofilters to the biofloc approach as biofiltration strategies. Sixteen 1-m3 round, polyethylene tanks were randomly assigned to four treatments, each of which had four replicate tanks. Eight biofloc systems were established: four using settling chambers for solids control (BF-S) and four using foam fractionators (BF-F). The other eight tanks used external biofilters; four had settling chambers (EB-S) and the other four had foam fractionators (EB-F). All 16 systems were stocked with 250 shrimp at an average size of 4.3 g which were grown for 85 days. There were no significant differences in shrimp production between treatments; however, variability was high in biofloc systems. Nitrite levels were significantly lower in systems with fractionators compared to systems with settling chambers. The concentrations of dissolved Na, Mg, Ca, Sr and Ba in the water were significantly reduced in treatments with settling chambers. The results of this study show that filtration choices significantly impact short- and long-term water quality and reusability but may not have much effect on shrimp production in the short-term.

Inorganic nitrogen compounds reduce immunity and induce oxidative stress in red seabream

In this study, the effect of ammonia derived from different stocking densities on immunological, hematological, and oxidative stress parameters was analyzed in the blood or liver of red seabream. Density- and time-dependent increases in inorganic nitrogen compounds were measured for 20 days by analyzing the three major inorganic nitrogen compounds, total ammonia nitrogen, nitrite nitrogen, and nitrate nitrogen. Three immunity parameters, alternative complement activity, lysozyme activity, and total immunoglobulin content were significantly decreased in the blood at the highest stocking density (10 kg m−3). The concentrations of hemoglobin and white blood cells were significantly decreased at 10 kg m−3, while there was no significant change in red blood cells. The significant increases in cortisol level and the enzymatic activities of alanine aminotransferase, aspartate aminotransferase, and alkaline phosphatase at 10 kg m−3 clearly supported inorganic nitrogen compounds-triggered stress. A significant elevation of lipid peroxidation value and depletion of intracellular glutathione were observed at 5 and/or 10 kg m−3 in the liver tissue. The hepatic enzymatic activities of antioxidant defense enzymes, catalase and superoxide dismutase were also significantly increased. When a protein skimmer removes the inorganic nitrogen compounds at the highest density, most parameters showed no significant change. Taken together, these results suggest that accumulated inorganic nitrogen compounds at the highest stocking density inhibit innate immunity and induce oxidative stress in red seabream. This information will be helpful to maintain homeostasis of red seabream by controlling immunity and oxidative status through inorganic nitrogen compounds removal in intensive culture condition.

Effects of foam fractionation and chemical disinfection on the removal of different microalgae cultures

The recent development of recirculation aquaculture systems (RAS) potentially allows more sustainable and controlled rearing conditions. However, control of suspended microparticles and microalgae in RAS is challenging, as uncontrolled blooms of toxic algae or heterotrophic dinoflagellates can have catastrophic impacts on the production of fish. In this study, we tested the potential of protein skimmers to remove microalgae. In 100 L batch tests, protein skimmers were tested separately and in combination with ozone (O3), ultraviolet (UV) or hydrogen peroxide (H2O2). Three different and distinct microalgae cultures were tested with densities from 30,000 to 120,000 algae cells/ml in a triplicated experimental setup. Trial 1 included twelve 24-hr replicated tests where protein skimmers with air or with two levels of ozone (low and high O3 exposure) were compared. The protein skimmer with air alone had a limited effect on the removal of microalgae compared to the untreated control algae tanks. When ozone and protein skimmers were combined, a clear additive effect was found, and all added microalgae were removed. Low O3 dosage and protein skimmers completely removed the algae cultures within 12 hr, while more than 95% of the algae were removed within 7 hr when a higher ozone dose was used. The second trial compared the removal capacity of protein skimmers in combination with UV, H2O2 and O3. These experiments showed no to limited additive effect of UV combined with protein skimming, but significantly increased removal efficiency (270% and 1,300%, respectively) was found when H2O2 and ozone were combined with a protein skimmer. The study showed an algae species-specific response to a protein skimmer with ozonation and provided information on the transition from reactivity and consumption to accumulation of ozone-produced oxidants.

Study on florfenicol-contained feeds delivery in Dicentrarchus labrax seawater recirculating and flowing aquaculture systems

Florfenicol (FLO) is the most commonly used antibiotic in aquaculture for various fish bacterial disease treatments. To ensure that low amounts of residue occur in cultured aquatic products, it is important to study the depletion of antibiotics in the process of aquaculture. Recirculating aquaculture system (RAS) is a promising aquaculture model with high water utilization that could effectively reduce nutrient concentrations; however, the fate of antibiotics under recirculating conditions is still unclear. In the present study, European seabass (Dicentrarchus labrax) were fed with FLO-medicated feeds at 10 mg/kg body weight/d for 10 d and the FLO depletion from water and tissues in RAS and flowing aquaculture system (FAS) cultures for 20 d were evaluated. The FLO residues in the RAS and FAS outlet peaked at 3 h and decreased to levels comparable to the pretreatment level at 12 h. With prolonged feeding, FLO was prone to accumulate in the RAS and peaked at 2.06 μg/L at 10 d of treatment, which was significantly higher than that in the FAS. To further compare the contributions among the water treatment units in the RAS, protein skimmer showed the most effective depletion of FLO, and then UV disinfection device and biofilter. Moreover, FLO showed the highest bioconcentration factors (BCF) values in the gill and the BCFs in muscle and liver from fish in the RAS were higher than that in the FAS. The present study reports the FLO depletions in a saltwater RAS for the first time and evaluates the contributions of different treatment units of the RAS on FLO depletion. The results showed the preliminary distribution of FLO in the RAS, which is valuable information for applying antibiotics in aquaculture and the designing water treatment units for RASs.

HPLC QUANTIFICATION OF LACTOPEROXIDASE IN THERAPEUTIC DAIRY WASTE ENRICHED BY BUBBLESEPARATION

Objective: The objective of this study was to enrich therapeutic proteins and remove pollutants from dairy wastewater for establishing foam fractionation as a lucrative unit operation.
 Methods: Dairy wastewater collected from dairy industry was processed to fat-free dried protein waste mass diluted to 1-liter feed by distilled water in different concentrations and foam fractionated by sodium dodecyl sulphate (surfactant) to enriched proteins extract (foamate) in a foam fractionator. Foamate were analysed to quantify total proteins and lacto peroxidase respectively. The efficiency was evaluated by varying parameters like pH, initial waste and ionic concentrations, the waste-surfactant mass ratio of feed and flow rate of gas (N2) through feed solution by several experiments. Heat of desorption (λ) and mass transfer coefficient (K) were determined as indicators of adsorptive bubble separation to foam phase governed by Gibb’s equation of adsorption isotherm.
 Results: The process was optimized at pH 5.5, initial feed concentration 500μg/ml, waste–surfactant mass ratio (1.5:1), gas flow rate (350 ml/min) and ionic concentration 0.1 gram-mole of NaCL per litre of feed with enrichment factor (49.09), percent recovery (98.18%) observed in foamate. One natural preservative specifically lactoperoxidase was quantified by RP-HPLC analysis as 0.49% (w/w) of total proteins at optimal condition. Heat of desorption(λ), mass transfer coefficient(K)were determined 3140cal/mol and 12.68* 10-9 mol/cal/cm2/s respectively at pH 8.5, initial feed concentration 500μg/ml and gas flow rate 350 ml/min.
 Conclusion: The method may be a useful unit operation for recovery of biomolecules and removal of toxic pollutants from industrial wastewater for coming days.

Foam fractionator as a tool to remove dissolved organic matter and improve the flocculation of the marine microalga Nannochloropsis oceanica

Microalgae have great biotechnological potential, yet they are difficult to harvest. Flocculation is a promising technology, but the dissolved organic matter (DOM) released by microalgae during growth interacts with the flocculant, hindering the process. This DOM is composed mostly of proteins and carbohydrates which may present a polarity ranging from hydrophobic to hydrophilic. In aquaculture, foam fractionators are routinely employed to remove DOM from cultures, improving the water quality. However, this equipment has never been employed in microalgae cultures. Therefore, the present study aimed to evaluate the use of the foam fractionator to remove DOM from a Nannochloropsis oceanica culture to improve the flocculation process. First, DOM accumulation was monitored for 33 days in a 330 L outdoor culture to characterize the dissolved organic carbon (DOC) and protein and carbohydrate contents. Samples from logarithmic (day 13) and stationary (day 29) growth phases were fractionated by polarity (hydrophobic, transphilic, and hydrophilic), the DOC and protein and carbohydrate contents of each fraction were measured, and flocculation was performed. Then the culture was treated with a foam fractionator at bench (11 L) and pilot scales (1600 L), and the composition and flocculation were compared with the non-treated culture. Proteins strongly hindered flocculation, and the foam fractionator was effective in removing this element and significantly improved the flocculation efficiency. Furthermore, N. oceanica cell integrity was not affected by the foam fractionator. These results indicate that DOM can be efficiently removed by foam fractionation, improving the microalgae harvesting process.

Growth and survival of juvenile Banggai cardinalfish (Pterapogon kauderni) reared under different salinities in recirculating aquaria equipped with protein skimmers

The Banggai cardinalfish (Pterapogon kauderni) is a small marine ornamental fish endemic to the Banggai Archipelago in Indonesia, listed as Endangered in the IUCN (International Union for the Conservation of Nature) Red List, and twice proposed for CITES (Convention on International Trade in Endangered Wild Species of Fauna and Flora) Appendix II listing. In addition to in-situ conservation, the Indonesian Action Plan (2017-2021) calls for ex-situ P. kauderni conservation, including the development of captive breeding. The accumulation of metabolic waste was suspected as a causal factor in high levels of mortality under all treatments in preliminary captive rearing trials. Protein skimmers can minimise the accumulation of potentially toxic nutrients, organic compounds, and pathogens. This research evaluated the effect of salinity on the growth and survival of juvenile P. kauderni in recirculating systems equipped with protein skimmers and periodical siphoning of waste with partial water change. Juvenile P. kauderni were obtained from the introduced population at Mamboro, Palu Bay, Central Sulawesi Province, Indonesia. Initial size range was 1-3 cm standard length (SL) and 0.105-0.329 g weight. Four salinity treatments (27 ppt, 30 ppt, 33 ppt, 36 ppt) with 5 replicates were applied, with 3 fish per experimental unit (aquarium, 20x30x20 cm, 7 litre capacity). Each fish was measured and weighed at the beginning and end of the 30 day experimental period. The fish were fed with mosquito (Culex sp.) larvae twice a day. The protein skimmers maintained high water quality and survival was high under all treatments, Survival was 100% at 27 ppt and 30 ppt. The 27 ppt treatment yielded the highest average growth (0.35 g in weight and 1.15 cm in SL). Our results show that juvenile P. kauderni grow faster at salinity levels lower than the average in endemic or introduced habitats of this species, and indicate that the use of protein skimmers can effective in promoting the survival of captive juvenile P. kauderni.

Design and performance of recirculating aquaculture system for marine finfish broodstock development

Tropical and subtropical climatic conditions in India present an ideal and unique opportunity for being the leader in tropical marine finfish aquaculture. However, the problem persist due to non-availability of marine finfish seed for the culture. In response to this problem, broodstock development of different tropical marine finfishes for seed production was started. The present study was undertaken to design a recirculating aquaculture system (RAS) and studying their performance in managing the various water quality required for the marine finfish broodstock development and breeding. The design of RAS, developed in the present study, included a broodstock tank, egg collection chamber, electrical pump, rapid sand filter, venturi type protein skimmer and biological filter. Two RAS were designed, one was stocked with a demersal fish species, orange spotted grouper (Epinephelus coioides) and the other was stocked with a pelagic fish species, Indian pompano (Trachinotus mookalee) at the rate 1 and 0.5 kg/m3 with a sex ratio of 1:1 and 1:2 (female: male) respectively. Various physio-chemical parameters, viz, total ammonia nitrogen (TAN), nitrite, nitrate, pH, alkalinity, temperature, free carbon dioxide (CO2) and dissolved oxygen (DO) of both tank water were analyzed to assess the performance of recirculating aquaculture system in maintaining the water quality. Gonadal development of the fishes was assessed and the spawning performance was recorded and finally, economic performance of the system was also evaluated. During the entire experimental period, mean monthly total ammonia nitrogen was less than 0.07 and 0.06 mg L−1 and mean monthly nitrite was less than 0.02 and 0.01 mg L−1 in orange spotted grouper and Indian pompano RAS tanks respectively. The pH (7.8–8.2), DO (>4 mg/L) and alkalinity (100–120 mg/L) were found to be in optimum range in both recirculating aquaculture systems. Carbon dioxide was found to be nil during the entire experimental period in both the systems. In fact these levels were comparable or less than that is reported as the permissible limits for broodstock development. Indian pompano and Orange spotted grouper matured and spawning was obtained with production of fertilized eggs round the year. Economic evaluation showed the price of 10,000 fertilized eggs of orange spotted grouper to be US $ 1.33. The design of RAS devised in the present study is efficient in controlling and maintaining optimum water quality for broodstock development of both demersal and pelagic finfishes. The fishes stocked in RAS attained final maturation and round the year spawning was obtained.