Progress 10/01/00 to 09/30/06
Outputs
The broad goal of this project has been to develop systems to use water in aquaculture more efficiently. In doing so, more aquacultured product is produced with less water and less impact on the environment. This project has focused on the characterization, treatment and reuse of water and wastewater coming from intensive aquaculture production systems. Early in the project, long term (changes over the production cycle) and short term (changes over 24 hours) studies were conducted to characterize the water and solid waste coming from a commercial scale recirculating aquaculture production systems. These wastes were found to be high strength and low volume flow's coming from the sludge collectors and drum screen filters of the system. Treatment options for thickening and removing the solids from the waste were investigated. These treatment options included drum screen filters, bead filters and settling basins. While settling basins were the simplest solution tested,
reduction of solids in the effluent was not optimum as the concentrations declined from input to outflow from 750 mg / L to 205 mg / L. While drum screens were able to reduce solids concentrations from 500 mg / L to below 100, the results were not consistent and maintenance of the system was a problem as the screens on the filter became overwhelmed with bacterial growth. The bead filters suffered the same fate as the filter bed clogged and became overwhelmed with bacterial solids preventing adequate backwashing. An improved technology was tested in 2005 that consisted of a geotextile bag and liquid polymer for coagulation of fine waste solids. Early results from this work indicate that over 97% of solid waste in the effluent flow stream can be removed with this technology. Suspended solids concentrations coming out of the geotextile bag are routinely below 30 mg / L and can be as low at 10 mg / L. Progress was made during this reporting period with the completion of a Masters Thesis
and graduation of a graduate student. This research evaluated wood chips and wheat straw as inexpensive and abundant resources for biofilter media in denitrification reactors. Nine 3.6-liter laboratory reactors filled with Kaldnes plastic media, wood chips, and wheat straw were built for treating both synthetic and real aquaculture wastewater in a series of experiments. The synthetic wastewater was formulated for 50, 120, and 200 mg NO3-N/L. Methanol was added as carbon source with amounts based on the nitrate concentration, while other chemical constituents were determined by characterizing actual wastewater and comparing with previous studies. The study showed that both wood chips and wheat straw were comparable to Kaldnes in terms of reducing nitrate. Approximately 99 per cent of nitrate (with influent as high as 200 mg/L) was essentially removed at pseudo-steady state. Denitrification rates averaged 1326 g NO3-N /m3/day for wheat straw, 1365 g N/m3/day for wood chips and 1361 g
NO3-N /m3/day for Kaldnes media. A manuscript has been accepted (with revisions) for publication detailing this research study.
Impacts
The aquacultural engineering program at NC State University provides design and technology development services to the agribusiness community in North Carolina. Technology from this program has also been implemented in other states. Results from this research allowed us to design an upgrade of the biofilter and oxygenation systems for six of the nine commercial tilapia production systems in North Carolina. As a result, feed rates to the production systems were increased while oxygen utilization by the systems was reduced by 50%. These design changes were implemented in similar facilities in Delaware and Georgia. The geotextile bag technology system assembled and tested in this project is being implemented on the tilapia production farms in North Carolina. The system, including supplies for one year will cost approximately $17,000 to install. Ongoing operating costs are estimated to be less than $3,000 per year. The process has been evaluated and approved by NC agencies
as a Best Management Practice (BMP). For the foreseeable future, farmers will land apply the water from this process. However, after further testing at the NC State Fish Barn, reuse of the water will save the farmers a significant amount of money by reducing the loss of salt, bicarbonate and heat that would be discharged in the effluent. We estimate these savings in salt and bicarbonate purchases alone could amount over $2,000 per month per farm.
Publications
- No publications reported this period
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Progress 10/01/04 to 09/30/05
Outputs
Progress was made during this reporting period with the completion of a Masters thesis and graduation of graduate student Willie Jones Saliling. This research evaluated wood chips and wheat straw as inexpensive and abundant resources for biofilter media in denitrification reactors. Nine 3.6-liter laboratory reactors filled with Kaldnes plastic media, wood chips, and wheat straw were built for treating both synthetic and real aquaculture wastewater in a series of experiments. The synthetic wastewater was formulated for 50, 120, and 200 mg NO3-N/L. Methanol was added as carbon source with amounts based on the nitrate concentration, while other chemical constituents were determined by characterizing actual wastewater and comparing with previous studies. The study showed that both wood chips and wheat straw were comparable to Kaldnes in terms of reducing nitrate. Approximately 99 per cent of nitrate (with influent as high as 200 mg/L) was essentially removed at
pseudo-steady state. Denitrification rates averaged 1326 g NO3-N /m3/day for wheat straw, 1365 g N/m3/day for wood chips and 1361 g NO3-N /m3/day for Kaldnes media. These values were not the maximum potential since the nitrate profile along reactors showed substantially higher rates in the lower half of the reactors. Treatment of real wastewater also showed comparable performance with that at the 50 mg NO3-N /L synthetic experiments. Carbon requirement was estimated by determining COD removed per nitrate reduced. COD/NO3-N ratios were: Kaldnes media (3.41 to 3.95) compared to wood chips (3.34 to 3.64) and wheat straw (3.26 to 3.46). COD/NO3-N ratios for the real wastewater were low (Kaldnes, 1.90; wood chips, 1.60; wheat straw, 1.44) compared to synthetic experiments. Effluent ammonia concentrations were near 0 mg NH3-N/L, and nitrite concentrations on the average were around 2.0 mg NO2-N/L. There was alkalinity production as a result of denitrification. Synthetic experiments yielded
alkalinity/NO3-N ratios between 3 and 4 while real wastewater had values near 6. Effluent pH ranged on the average from 8 to 9.5 while the oxidation-reduction potential declined to as low as -150 mV. Wood chips lost 16.2% of its initial mass while wheat straw mass was reduced by 33.7%. There were physical signs of degradation like discoloration and structural transformation (some wood chips easily broke into smaller pieces and wheat straws reduced to fibrous strands). Both wood chips and wheat straw exhibited reduction of C/N ratio. Changes of lignin were also observed for both media. The reactors also maintained diverse bacterial communities. A denaturing gradient gel electrophoresis (DGGE) showed several ribotypes that differed with media types and with height in each reactor column.
Impacts
Biological Filtration media is expensive. Currently available plastic media such as the one used in this study as a control costs in excess of US$1,500 per cubic meter. In comparison, the wood chips used in this study cost US$19 per cubic meter and the wheat straw cost US$6 per cubic meter. Results of this study suggest that wood chips would be a cost effective alternative to the more expensive plastic media. Low-cost, large-scale denitrification reactors will make the removal of nitrogen from wastewater possible in a simple on-farm application. The removal of nitrogen from the wastewater will reduce the land required to dispose of waste effluents and in turn significantly reduce the cost of waste treatment for intensive aquaculture farms.
Publications
- Saliling, W.J.B. 2005. Denitrification of aquaculture wastewater using agricultural by-products as biofilter media. Masters Thesis, North Carolina State University, Raleigh, NC, USA.
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Progress 10/01/03 to 09/30/04
Outputs
Eight thousand yellow perch were reared in a recirculating system located in a greenhouse. A twice replicated study of yellow perch growth of two diets was completed. The control diet was a 42% protein, 10% fat formulation. The test diet was a 38% protein, 8% fat. Two tanks each of 2000 fingerlings were grown to market size. No statistical difference in growth was detected in these feed trials. A graduate research assistant is conducting a study in the use of agricultural byproducts for use as biofilter media in denitrification processes. The student has created 9 identical bench-scale reactors that tested three different media's in triplicate. The control media was a commercially available plastic media. The two test medias were hard wood chips and wheat straw. After a 5 month trial, very high denitrification rates were achieved in all reactors. The denitrification rates in the reactors with wheat straw and wood chips were equal to that of the commercial control
media. Analysis of degradation of the agricultural byproducts and further data analysis are ongoing and will be reported in the students thesis by May 2005. An on farm test of a large scale denitrification trench filled with hard wood chips has been ongoing. Experience with this system indicates that the wood chips are susceptible to clogging from solid wastes that may enter with the wastewater. Efforts to remove these wastes with bead filter technology have failed. Further research will look for simple, low cost means for removal of these solids.
Impacts
Feeds are one of the largest single costs in the production of fish. Diets containing higher levels of protein and fat cost more than those with less. The results of this study will directly impact the current yellow perch industry with cost savings in the diets used. Additionally, diets with higher protein levels will produce more ammonia nitrogen in the wastewater. Higher levels of ammonia produced by the fish require larger biofilters to be used in the culture system. Results from this study will save farmers the initial investment in larger biofilters. The results from the denitrification study provide encouragement that a lower cost biofilter media can be used for this purpose. Wood chips can be purchased at a fraction of the cost of the commercial plastic media. The results from this study indicate that very high rates of denitrification are possible with agricultural byproducts (with the addition of a carbon source). As such, the size of the reactors needed to
treat whole end of pipe waste flows may be far smaller than originally anticipated. The on farm application of this technology will also save space within the overall waste treatment system. Removal of the inorganic nitrogen from the waste stream allows the irrigation field for water disposal to be smaller. That is, the field is sized to retain the available water, not sized to uptake the available nitrogen.
Publications
- Losordo, T.M., Ray, L.E. and DeLong, D.P. (2004). Flow through and recirculating systems. Chapter 18 In: Tucker, C. and Hargreaves, J. eds., The Biology and Culture of Channel Catfish. Elsevier Scientific, Amsterdam, The Netherlands.
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Progress 10/01/02 to 09/30/03
Outputs
Progress this year has been made on many fronts; evaluating biofilters, evaluating diets for yellow perch, and improving wastewater treatment technology. A media, commonly used in the ornamental industry (Matala Mat), is being tested as a trickling filter biofilter media and a submerged upflow biofilter media. No published data exists for the nitrification capacity of this media. To date the media has been tested as a trickling filter media. The results are comparable with other media available to the industry. These results will be compared with the nitrification resulting from the same material used in a submerged upflow configuration. These experiments will be conducted in 2004. Yellow Perch were grown on two diets in a recirculating system in a well-shaded greenhouse. Four tanks were used with replicates of two diets, 42% protein, 16% fat, and 40% protein,10% fat. Growth rates, feed conversion and visceral fat deposition were compared. These studies were just
coming to a close at the end of this reporting period. Results to date indicate no better performance from the higher protein and fat diet in either growth rate or FCR. Visceral fat deposition results were not available at the writing of this report. The waste treatment project continued this year with an effort to develop end-of-pipe technology to reduce or completely eliminate nitrate nitrogen from the effluent entering the storage pond. In preliminary tests, a newly commercialized Drop Bead Filter was tested as a pretreatment option for reducing suspended solids. Results indicate that bacterial growth was too fast for this technology as the bead filter clogged with heterotrophic bacteria. On a more encouraging note, low cost agricultural byproducts were tested as a biofilter media for use in denitrification filters. A preliminary test was conducted with wheat straw and hard wood chips. Results will be available in the next reporting period.
Impacts
Feeds are the single largest variable cost in the aquaculture production of finfish. The findings of the yellow perch diet study will save money for our existing and future yellow perch farmers as the lower protein and fat formulation is the less expensive diet. The results of our study on end-of-pipe denitrification were put into use in the development of a prototype denitrification trench on a commercial Fish Barn site in North Carolina. Tests of this full scale (118 ft) reactor were encouraging. Nitrate nitrogen was reduced by 98% in preliminary sampling. This type of technology will allow current and future farmers to meet or exceed state and federal environmental regulation for the foreseeable future.
Publications
- Losordo, T.M., D.P. DeLong, and P.W. Westerman. 2003. Appropriate designs for the on-site treatment and utilization of wastes in rural, farm-based, freshwater recirculating systems: An overview of critical considerations with an emphasis on economic viability. An extended published abstract of a keynote presented at the European Aquaculture Society Annual Meeting, Trondheim, Norway, August 8 through 12, 2003.
- Copeland, K.A., W.O. Watanabe, P.M. Carroll, K.S. Wheatley, and T.M. Losordo. 2003. Growth and feed utilization of captive wild black sea bass Centropristis stiata at four different densities in a recirculating tank system. Journal of the World Aquaculture Society. Vol . 34, No. 3.
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Progress 10/01/01 to 09/30/02
Outputs
We have made progress in a number of focus areas during this reporting period. We have begun a wastewater characterization and treatment effort that focuses on end of pipe treatment of wastewater coming from our large-scale recirculating fish production system. Our focus this year has been to evaluate methods for the reduction of suspended solids and organic nitrogen leaving the facility and emptying into a storage pond. Waste water sampling has shown the suspended solids concentration leaving the fish production system to average 457 mg / L (sd= 112). The organic nitrogen measured as Total Kjeldhal Nitrogen (TKN) averaged 26.5 mg / L (sd = 4.8). Last year, a settling basin was evaluated for it's capacity to remove and retain suspended solids and organic nitrogen. This year a drum screen filter with a 60 micron screen was used in place of the settling basin. The drum screen filter has been found to reduce the suspended solids concentration over this reporting period
by 77% (sd = 12%). Similarly, TKN concentrations have been reduced by an average of 64% (sd = 10%). Another area of focus is the continued development and evaluation of biological filters for marine fish production. This work was completed at the New South Wales Fisheries Centre as a follow on study to work completed last year. The results of this years study showed that in this project, mixed bed biofiters used in this project were fully mature and functional only after a period in excess of 300 days. The results of this years study showed that the biological filters in full strength seawater had only 20% of the nitrification capacity of a similar filter used in freshwater.
Impacts
Results of research efforts in this project have been applied at a new fish production facility in North Carolina. The project investigators have designed and overseen the construction of North Carolina's first large-scale, indoor, recirculating Yellow Perch production facility. This facility is the first of a two phase project that is designed to produce 200,000 pounds of yellow perch per year. Results of our study on marine biological filters have significant implications for the sizing of biofilters for use in salt water. Our data suggests that these filters will need to be as much as 5 times larger than those used in similar freshwater applications.
Publications
- Watanabe, W.O., T.M. Losordo, K. Fitzsimmons, and F. Hanley. 2002. Tilapia Production Systems in the Americas: Technology Advances, Trends, and Challenges. Reviews in Fisheries Sciences, 10(3&4):465-498.
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Progress 10/01/00 to 09/30/01
Outputs
Recirculating aquaculture fish production systems are used in water limited areas of North Carolina (NC) and the USA. In 2001, nine large-scale commercial aquaculture facilities in NC used this type of technology. Improved nitrifying biological filters and waste removal components are needed to enhance the biological and financial performance of these systems. During the reporting period, the investigators on this project began evaluation of the nitrifying characteristics of moving bed biological filters. A site in NC for freshwater systems is currently under construction. A site in Australia was developed and experiments were run in fully saltwater conditions. The results of the marine moving bed biofilter studies indicate that nitrification rates in salt water are nearly 1/10 of that reported in freshwater systems. Nitrification rates in the range of 0.01 - 0.05 grams of TAN per square meter of media surface area per day were measured. Similar fresh water systems
routinely exhibit nitrification rates of 0.25 - 0.50 grams of TAN per square meter of media surface area per day. Freshwater nitrification rates for this type of filter will be developed during 2002 in North Carolina.
Impacts
The results of this work will provide baseline data for improvements in the management of these types of filters. Additionally, the results of this study will directly impact on the design and sizing of moving bed reactors for marine finfish production. The implications of these results are that biofilters for marine production systems must be significantly larger than for freshwater systems of similar production capacity. These results, once published, should keep designers of such systems from under-sizing biological filtration components in the future.
Publications
- No publications reported this period
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