Steven T. Summerfelt

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

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

Ozonation and UV irradiation—an introduction and examples of current applications

This paper was written to introduce the 2001 AES Issues Forum’s ‘Ozone and UV Treatment ’ session by providing an overview of ozone and ultraviolet (UV) irradiation technologies as well as several examples of current ozone and UV irradiation applications in aquaculture.

Review of circular tank technology and management

Large cost savings have been achieved in the production of food fish with the use of larger systems and enhanced production management strategies. These trends have also included the use of large circular culture tanks because of their many advantages for food fish production. Circular tanks make good culture vessels because they can provide a uniform culture environment, can be operated under a wide range of rotational velocities to optimize fish health and condition, and can be used to rapidly concentrate and remove settleable solids. The flow inlet and outlet structures and fish grading and/or removal mechanisms should be engineered to reduce the labor requirements of handling fish and to obtain effective tank rotational characteristics, mixing, and solids flushing. This paper reviews and discusses the rationale and criteria needed to design circular culture tanks. In addition, the implementation of continuous production and satiation feeding strategies within circular culture tanks is discussed because of their large and often under-emphasized effect on overall system productivity.

Aquaculture sludge removal and stabilization within created wetlands

The objective of this research was to investigate treatment of the concentrated solids discharge produced during clarifier backwash within an aquaculture facility. Solids removal and stabilization were investigated within two types of created wetlands where water flowed either: (1) vertically, down through a porous substrate; or (2) horizontally, over soil and through plant hedges. Six 3.7×1.2×0.8-m (L×W×H) wetland cells were used to provide three replicates for both types of wetland. Approximately equal numbers of vetiver grass (Vetiveria zizanioides) tillers were planted on both wetlands types in November of 1994. Sludge (7500 mg l−1 solids) was loaded onto both wetland types six times day−1, with no scheduled drying cycle, from 12 May 1995 until 28 February 1996. Sludge was applied at a rate of about 1.35 cm day−1, or about 30 kg dry solids m−2 year−1. Results from this short study indicated that the vertical flow and horizontal flow wetlands, respectively, removed 98 and 96% TSS, 91 and 72% total COD, and 81 and 30% dissolved COD. Both types of wetland cells removed most (82–93%) of the total kjeldahl nitrogen, phosphorus, and dissolved phosphate. Measurements of sludge depths and TVS at the end of the study indicated considerable mineralization occurred in the wetlands; stored sludge at the end of the study had 50% less TVS than untreated sludge.

Ozonation of a recirculating rainbow trout culture system ' I. Effects on bacterial gill disease and heterotrophic bacteria

Ozone was added to water in a recirculating rainbow trout (Oncorhynchus mykiss) culture system just before it entered the culture tanks in an attempt to reduce the numbers of heterotrophic bacteria in system water and on trout gills, and to prevent bacterial gill disease (BGD) in newly stocked fingerlings. During four &week trials, ozone was added to the system at a rate of 0.025 or 0.036-0.039 kg ozone/kg feed fed. In the control, where no ozone was added, and in previously published research, BGD outbreaks occurred within two weeks of stocking, and these outbreaks generally required three to four chemotherapeutant treatments to prevent high mortality. In three of four trials where ozone was added to the system, BGD outbreaks were prevented without chemical treatments, but the causative bacterium, Flacwbacterium branchiophilum, still colonized gill tissue. The one ozone test where BGD outbreaks required two chemical treatments coincided with a malfunction of the ozone generator. Although ozonation did reduce BGD mortality, it failed in all trials to produce more than a one log ,[I reduction in numbers of heterotrophic bacteria in the system water or on gill tissue. Failure of the ozone to lower numbers of heterotrophic bacteria or to prevent the causative BGD bacterium from occurring on gills was attributed to the short exposure time to ozone residual (35 s contact chamber) and rapid loss of oxidation caused by levels of total suspended solids. Rationale for ozone’s success at preventing BGD mortalities are not fully understood but may in part be due to improved water quality. Use of the lower ozone

Review of Ozone Processes and Applications as an Oxidizing Agent in Aquaculture

Abstract Ozone has been used in a range of aquaculture applications related to disinfection and improving water quality. Ozone has seen wide use because it is a powerful oxidizing agent that has a rapid reaction rate and few harmful reaction products. This paper reviews the application of ozone within aquaria and in aquaculture systems that use single-pass or recirculated water. The issues and mechanisms required to use ozone are reviewed, with particular emphasis on the processes of ozone gas generation and gas-to-liquid absorption, the contact time for reaction, and the removal of residual ozone. In addition, the toxicity of ozone to humans and to aquatic organisms is discussed, as well as techniques to monitor or control ozone in both the gaseous and aqueous phases.

Ozonation of a recirculating rainbow trout culture system II. Effects on microscreen filtration and water quality

Ozone was added to water in a recirculating rainbow trout (Oncorhynchus mykiss) culture system just prior to the culture tanks in order to oxidize nitrite and organic material, improve overall water quality, and assist removal of solids across the microscreen filter. Data from four &week studies on ozonation and an &week no ozone control indicated that adding ozone reduced the mean concentration of TSS by 35%, COD by 36%, DOC by 17%, and color by 82% within the water entering the culture tanks. Additionally, ozone reduced the mean nitrite concentration by 82% within the culture tanks. Adding ozone did not affect turbidity. Changes brought on by ozonation, particularly as it affected the characteristics of the suspended solids, also improved suspended solids removal across the Triangel’” filter by an average of 33%. In addition, adding ozone decreased plugging of the microscreen filter panels, as indicated by an average of 35% fewer filter wash cycles, 53% less filter sludge flow produced, and 79% more settled solids volume in the Triangel’” filter effluents. Comparison of two different ozone dosing rates indicated that adding ozone to our recirculating system at a rate of 0.025 kg ozone per kilogram feed was

Diseases encountered in rainbow trout cultured in recirculating systems

Abstract Recirculating systems create unique environments for fish culture which may provide favorable conditions for disease occurrence or the reproduction of opportunistic microorganisms. Stressful conditions in recirculating systems, such as poor water quality or high stocking densities in the culture tanks, may contribute to disease outbreaks. Non-infectious problems, including high levels of ammonia, nitrites, carbon dioxide, suspended solids, or ozone residual levels have also caused mortalities in recirculating systems. The diseases encountered in rainbow trout ( O. mykiss ) cultured in recirculating systems include: those caused by bacteria (bacterial gill disease, furunculosis, bacterial kidney disease, fin rot), parasites ( Gyrodactylus, Chilodonella, Trichodina, Epistylis, Trichophrya, Ichthyopthirius, Ichtyobodo , proliferative kidney disease, amoebic gill infestation, Coleps ), fungi ( Saprolegnia ), and viruses (infectious pancreatic necrosis, viral hemorrhagic septicemia, and infectious hematopoietic necrosis). Treatments with chemotherapeutants in the water or feed in a recirculating system present special considerations; the main one is whether the biofilter will be treated and how the chemicals could affect its function. Management practices designed to prevent the occurrence of diseases or the degradation of water quality are critical to a successful recirculating facility. The introduction of known pathogens with infected fish should be prevented either by hatching eggs at the facility from disease-free broodstock, or by purchasing fingerlings from disease-free certified broodstock and by creating a quarantine period. Each recirculating facility should design a protocol for prevention of and control of fish diseases with the aid of a fish health professional, based on the generally accepted principles of fish health management.

Mechanistic approach to phytoremediation of water

Conventional thinking regarding the use of food crops to clean aquaculture effluents has been that plants cannot remove nutrients in water to low levels without a reduction in productivity and quality. Because greenhouse space is expensive, productivity is critical for a profitable operation. A production strategy, called the conveyor production system (CPS), was developed using thin-film technology for plant production in dilute aquaculture effluents. With the CPS, young plants were positioned near the solution inlet in a gutter receiving the effluent and moved progressively, like along a conveyor belt, towards the outlet as they grew. Luxury consumption by lettuce plants (Lactuca sativa L. cv. Ostinata) enabled them to store P in their tissues early in their growth cycle for use later as water P levels decreased and influx could no longer meet current demands. If water is distributed in a horizontal plug-flow pattern, without the CPS, all nutrients will be luxury consumed at the inlet, making nutrients limiting at the outlet and significant greenhouse space will be dedicated to growing plants that have no market value. The object of this study was to construct and operate a pilot-scale CPS, collect data demonstrating its potential to clean effluent and produce a marketable product, and develop a mechanistic model describing the process. Greenhouse studies demonstrated that by using the CPS, phosphorus could be reduced from 0.52 to <0.01 mg l−1 by lettuce without an apparent reduction in production or quality. The mechanistic model described in this paper simulated experimental data collected during the operation of the CPS growing lettuce and defines critical data necessary for the general comparison of effluents for treatment.

Distribution of Off-Flavor Compounds and Isolation of Geosmin-Producing Bacteria in a Series of Water Recirculating Systems for Rainbow Trout Culture

Abstract Preharvest off-flavor in aquaculture products results in large economic losses to producers due to delayed harvest. The common off flavors “earthy” and “musty” are due to the presence of geosmin and 2-methylisoborneol (MIB), respectively. Although certain species of cyanobacteria are responsible for these problems in pond-cultured fish, the microbial sources of geosmin and MIB in recirculating aquaculture systems (RASs) are still being explored. In this study, we investigated (1) the distribution of geosmin and MIB within six replicated RASs producing rainbow trout Oncorhynchus mykiss and (2) the microorganisms responsible for earthy off-flavor in the flesh of RAS-cultured trout. Water, biosolids, and fish samples were collected when fish were at maximum feed levels and before harvest. Each RAS contained a fluidized-sand biofilter, a cascade aeration column, a low-head oxygenation (LHO) unit, an LHO sump, a 5.3-m3 culture tank, a drum filter, a pump sump, and a heat exchanger. Solid phase microex...