Ronald F. Malone

Use of floating bead filters to recondition recirculating waters in warmwater aquaculture production systems.

Abstract Floating bead filters (FBFs) are expandable granular filters that display a bioclarification behavior similar to sand filters. They function as a physical filtration device (or clarifier) by removing solids, while simultaneously encouraging the growth of bacteria that remove dissolved wastes from the water through biofiltration processes. Presently, there are two classes of FBFs that exist. Hydraulic and air washed units fall into the ‘gently washed’ category, which display reduced biofilm abrasion during backwashing and must be washed at a high frequency. Conversely, propeller-washed and paddle-washed filters inflict damage to a relatively heavy biofilm during backwashing, and are considered ‘aggressively washed’. FBFs capture solids through four identifiable mechanisms: straining, settling, interception, and adsorption. In the biofiltration mode, bead filters are classified as fixed film reactors, where each bead becomes coated with a thin film of bacteria that extracts nutrients from the recirculating water as it passes through the bed. In this paper the authors first establish application categories and parameters for recirculating system use, then give criterion for the sizing of recirculating system components in tabular form. Sizing variables for FBFs are normalized to the feed application rates, and the primary method for the sizing is based on a volumetric organic loading rate. Evaluation parameter equations are also given for comparison of bioclarifier performance. These equations include volumetric TAN conversion rate (VTR), the volumetric nitrite conversion rate (VNR), and the volumetric oxygen consumption rate of the bioclarifier (OCF).

A Sodium Bicarbonate Dosing Methodology for pH Management in Freshwater-Recirculating Aquaculture Systems

Abstract High-density water-recirculating aquaculture systems with hydraulic retention times above about 5 d must be monitored for alkalinity, and in the vast majority of cases, the alkalinity must be adjusted upwards to assure maintenance of desirable pH levels. Sodium bicarbonate is the preferred additive for increasing alkalinity because it is inexpensive, dissolves rapidly, and is safe for both personnel and fish. The high rate of carbon dioxide production in such systems requires significant stripping capabilities and dictates the appropriate alkalinity concentrations in this CO2-enriched environment. The methodology presented for alkalinity adjustment uses measurements of pH and alkalinity to obtain an estimate of the system CO2 level, which, in turn, is used to define the alkalinity concentration required to reach a targeted pH. A dosage table facilitates determination of the amount (g) of sodium bicarbonate to be added to reach the targeted pH for a variety of system sizes. The charts, which are d...

Algae removal by fine sand/silt filtration

Abstract A laboratory scale study was undertaken to determine the potential of a method of filtering algae from water using fine sand/silt as the filter media. Five median sand sizes (0.064–0.335 mm) and four bed depths (3.175–12.700 mm) were examined in constant head experiments with the algae Scenedesmus quadricauda. A total of 46 experiments were conducted with continuous measurements of filtration rate, head loss and effluent quality. All media with median sand sizes at or below 0.200 mm gave consistently high algae removal rates. The average removal was 97.27% (based on fluorescence) with a low average initial head loss across the filter media of 7.3 cm (median grain size diameter of 0.200 mm with the bed depth of 3.175 mm). Initial filtration rates obtained in the experimental apparatus were as high as 226 m3 m−2–day−1 (3.84 gpm ft−2), comparable to conventional sand units. Run times were short due to surface clogging of the media. No chemical addition was required to obtain high removal levels.

Evaluation of air-lift pump capabilities for water delivery, aeration, and degasification for application to recirculating aquaculture systems

Abstract A methodology is demonstrated for evaluating the feasibility of using air-lift pumps for water movement, aeration, and degasification in a recirculating aquaculture system. A set of empirical equations are presented modeling the performance of a 5.08-cm (2″) diameter air-lift submerged 91.44 cm (36″) with a 15.24-cm (6″) lift operated at 28–142 l min −1 (1–5 scfm) of air injection. A steady state mass balance on oxygen and carbon dioxide, equating the system requirements to the air-lift capabilities is illustrated. Using the empirical relationships developed and standard methods to estimate system O 2 demand and CO 2 production, equations are derived to calculate steady state DO and DC concentrations for any number of air-lifts used in a given recirculating system. The predicted air-lift performance in a typical system indicates the water delivery capacity for low head applications is significantly above the gas exchange capabilities. It is recommended that air-lifts be designed for water delivery and that the demonstrated methodology be used to estimate their supplemental aeration and degasification performance. Open-water aeration is shown to be more energy efficient than aeration using air-lifts. The data suggests that, for blown air systems, when the aeration requirements are met, the carbon dioxide stripping requirements are also. Suggestions for designing recirculating systems utilizing air-lifts are also presented.

Effect of Feeding Strategies on Production Characteristics and Body Composition of Florida Pompano Reared in Marine Recirculating Systems

Abstract The effect of feeding strategies on production characteristics and body composition of Florida pompano Trachinotus carolinus reared using marine recirculating systems was evaluated in three growth trials (water temperature, 27–29°C; salinity, 23–28‰). A commercial diet (53% protein, 13% lipid) was fed in each trial. In trial 1, mean final weight of juveniles fed 5% of body weight per day (bw/d) in two, three, or six feedings for 38 d was significantly greater than that of Florida pompano fed once daily. In trial 2, Florida pompano that were fed twice daily to apparent satiation (AS) were significantly larger after 54 d than fish fed a fixed ration of 5% bw/d, regardless of initial stocking density (1.3 or 2.6 kg/m3). In trial 3, mean final weight of Florida pompano fed to AS four times daily for 133 d was significantly greater than that of fish fed to AS twice daily. Feeding rate and frequency did not affect feed conversion efficiency or body composition and had minimal effects on specific growth...

Modeling the major limitations on nitrification in floating-bead filters

A model was developed and calibrated to experimental data, to formulate a theoretical description of nitrification in bead filters. The model results were consistent with the literature, indicating that the inverse relationship between solids accumulation and nitrification is mediated by an oxygen limitation. This result was central to an explanation of why differing optimal backwash intervals in gently- and aggressively-washed filters are related to: (1) differences in harvest fraction, which fixes the relationship between backwash interval and interstitial solids concentration and (2) differences in biofilm retention, which controls the average biomass age thereby determining total biomass concentration.

Nitrification performance of a bubble-washed bead filter for combined solids removal and biological filtration in a recirculating aquaculture system

Laboratory studies were conducted to evaluate the nitrification performance of a bubble-washed bead filter as affected by backwashing frequency and feed loading rate. The bubble-washed bead filter was used for combined solids capture and biological filtration in a recirculating tilapia (Oreochromis niloticus) culture system. The filter was tested at feed loading rates of 16, 24, and 32 kg day−1 m−3 beads. Backwashing frequencies varied and had to be adjusted at each feed loading rate for satisfactory nitrification, to maintain total ammonia nitrogen (TAN) and nitrite–nitrogen (NO2–N) at concentrations below 1.0 mg l−1. In general, more frequent backwashing improved filter performance, and was necessary at higher feed loading rates. It was essential to provide adequate flow through the bead filter (at least 50 l min−1 kg-feed−1 day−1) to keep the effluent DO greater than 2 mg l−1 just prior to backwashing. At the highest feed loading rate tested of 32 kg day−1 m−3 beads, favorable performance was observed at five backwashes in a 24 h period, achieving average areal TAN and NO2–N conversions of 331 and 451 mg m−2 day−1, equivalent to volumetric conversions of 380 g TAN day−1 m−3 beads and 518 g NO2–N day−1 m−3 beads.

Chemical addition for accelerated biological filter acclimation in closed blue crab shedding systems

Abstract Heavy loading of commercial crab shedding systems is a major problem at the beginning of the softshell crab season if the biological filters are not properly acclimated. Thus methods that can be used to accelerate filter acclimation in a commercial setting are desirable. Experimental shedding systems with submerged rock filters impacted by media size, commercial additives containing nitrifying bacteria, and chemical addition were examined. Filters acclimated with crabs took 35 days to adjust to base line water quality conditions. The filters demonstrated the ability to be increased to full design loading if acclimated with 25% of the shedding system design. Filter media size and addition of concentrated nitrifying bacteria did not have any significant effect on acclimation time of the nitrification beds. Addition of ammonia to simulate loading acclimated a biological filter without the use of animals, but did not shorten the acclimation time. The most promising avenue of research is the addition of ammonia and nitrite in combination to stimulate growth in both species of nitrifying bacteria simultaneously. Nitrite addition during startup of a biological filter reduced the acclimation period by 10 days (or 28%).

Microalgal production using a hydraulically integrated serial turbidostat algal reactor (HISTAR) : a conceptual model

Abstract A hydraulically integrated, serial turbidostat algal reactor (HISTAR) was mathematically modeled and developed for the mass production of microalgae. HISTAR, which hydraulically links precisely controlled turbidostats with continuous-flow stirred-tank reactors (CFSTRs) into a single production technology, was conceptualized emphasizing contaminant mitigation at the design stage to maintain system stability. This paper discusses the conceptual basis for the development of HISTAR and presents a theoretical overview of the CFSTRs. Mathematical modeling, using first-order algal growth kinetics combined with CFSTR reactor kinetics, was used to investigate the effects of system dilution rate, D s ; net algal specific growth rate, U a ; number of reactors, N ; input algal biomass, X i ; and contaminant concentration, C n , on algal productivity, as well as local dilution rate, D n , on suspended contaminant washout. The simulation results allowed the determination of preliminary design ranges for prototype development.

Submerged rock filter evaluation using an oxygen consumption criterion for closed recirculating systems

Abstract The supply of dissolved oxygen for the bacteria has been observed to be the principal factor limiting the carrying capacity of submerged rock filters used in high density recirculating culture systems. Oxygen concentrations in a submerged rock filter must not fall below 2 mg liter−1 if complete nitrification is to be assured. A mass balance on oxygen is used to develop relationships defining the rock volume and flow rates required for the nitrification beds used in blue crab (Callinectus sapidus Rathbun) shedding systems. These relationships are used to examine the impact of various filter configurations on performance. Of the six designs evaluated, those employing recirculation with supplemental aeration are shown to be the most successful. Under the conditions imposed in this analysis, it was observed experimentally that 1 m3 of 2 cm limestone could support bacterial consumption of 1·2 kg O2 day−1 without limitations from other parameters. Elimination of oxygen limitation leads to filter failure by physical clogging or pH decline. Further improvements in carrying capacity can be realized by solids removal which is shown to reduce oxygen demand in a submerged rock filter tested on blue crabs by approximately 30%. The criterion developed is applicable to a wide variety of culture systems.