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BIOFILTERS IN RECIRCULATION AQUACULTURE SYSTEM

NATHAPORN AREERACHAKUL

Faculty of Industrial Technology, Suansunandha Rajhabhat University, Bangkok, Thailand E-mail: nathaporn.ar@gmail.com

Abstract - Biofilter can be an effective solution for producing high quality water and saving water for recirculation aquaculture system. This paper gives an overview on the concepts, merits and demerits of the typical biological filtrations for aquaculture such as submerged filter, trickling filter, rotating filter, bead filter and fluidized bed filter. In this paper, a concept design of a trickling biofilter for barramundi (Lates Calcarifer) recirculation systems in New South Wales Fisheries is discussed in details. Keywords - Recirculation aquaculture system, biofilter, concept design I. INTRODUCTION Aquaculture industry has been growing rapidly. The industry had increased worldwide by 9.2% from 1970 to 2000. In Australia, the value of aquaculture production has increased by more than 15 per cent each year between 1989 and 1999 (ABARE, 2004). Basically, aquaculture is classified into intensive and extensive aquaculture system. While extensive aquaculture system depends mostly on natural condition with no or a little input and low production level, intensive aquaculture refers to systems in which most of environmental conditions are controlled (Ladon, 1992). Recirculation system is a typical sample of intensive aquaculture system which plays an important role in aquaculture industry to supply aquatic products under controlled cultivation condition. In aquaculture, the productivities of aquaculture depend significantly on the quality of feeding water. The production of an aquaculture system can be influenced by both physical and chemical characteristics of water such as suspended solids, temperature, dissolved gas, pH and potential toxic substrates (Laden, 1993). Chen et al. (1994) showed that the suspended particles on the recirculation system can damage fish gills, mechanical clogging of filter, mineralization to produce ammonia and increasing oxygen demand when the particles decay. In order to assess the quality of water in the fish farms, many parameters are employed. Dissolved oxygen (DO) is considered as the most critical and limiting factor in small scale aquaculture. The proper level of DO in water warrants to the survival and development of fish and for aerobic decay of organic matters. In addition, Biochemical Oxygen Demand (BOD) and Total Organic Carbon (TOC) are among the most popular parameters used to measure the amount of organic presented in water. The high concentration of organic matter in water impairs turbidity, odour and increases the growth of pathogens. According to the guideline of the Australian and New Zealand Environment and Conservation Council (ANZECC) for Fresh and marine Water quality (2000),

DO level should be more than 5 mg/L and BOD5 less than 15 mg/L. To control the quality as well as to save water in the aquaculture recirculation, especially in the small scale farm, several water treatment processes are applied such as screening, filtering, floating, settling and disinfection processes. Screening and settling techniques are simple and usually used in the primary treatment for removing large suspended solids. Filtration, especially biofilter is used in the latter stage of water treatment in recirculation system. Deep bed filtration with sand and activated carbon was used globally for many years in which micro-organisms grow on the filter media and form a biological layer. However, activated carbon is used widely due to their capacity of adsorption. Different kinds of biofilter media are used such as sand, granular activated carbon and bead etc. II. TYPICAL BIOFILTER IN RECIRCULATION AQUA SYSTEM Many types of biofilter have been applied in recirculation aquaculture system. Each of them has both advantages and disadvantages that should be considered in the design of the fish farm. Some typical types of biofilter are submerged filter, trickling filters, rotating filter, bead filter and fluidised bed filter. Submerged filter is versatile, resilient and easy to operate, build and maintain. Submerged filter is usually used for small scale aquaculture systems. Filter media in the submerged filter is fully submerged under the water surface, thus the oxygen supplied for the development of biofilm comes from water. The efficiency of the filter depends on retention time and media type. Therefore, Smith (2003) suggested that the flow path through a submerged filter should be as long as possible with a long thin raceway as the best option. A potential problem of submerged filer is the “dead zones"- an area that microbial population do not receive enough nutrient and oxygen. However, this problem can be overcome by increasing flow rate to make sure even water distribution throughout the filter.

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Trickling filter is another form of biofilter in which the media is wet but not submerged and provides the interface for the growth of the biofilm. Filter media is usually highly porous with a large surface for colonized bacteria. Trickling filter is effective in treating nutrient. The treatment efficiency depends on the filtration rate. The main cost of operating the filter is the energy to pump water to the top of the filter. This expense can be reduced by using a wider low filter but more space is required.

Table 1 Comparison of different types of biofilters for

aquaculture Water for aquaculture system can be effectively treated by rotating contactor. A cylinder with the biofilm fixed on its surface is partially submerged in the influent, and is rotated at a constant rate. The biofilm will alternately contact to the air and then submerge when the cylinder rotates. This kind of biofilter has a high efficiency in removing biodegradable particles, requires little energy to operate and can be placed in the culture tank to save space (Smith, 2003). However, the commercial

systems are costly and the biofilm can be dry if there is a power or mechanical failure.

Figure 1. Five typical biofilters in recirculation aquaculture

system Bead filters are a quite new and popular type of biofilter that using small bead of plastic (polyethylene or polypropylene) as filter media. The beads float in the wastewater that flows in an upward direction with air, water jets or mechanical means (Wheaton et al., 1994). The advantages of beads are their large surface area to volume ratio to support the development of biofilm and small enough to trap most of the large suspended solids. A potential problem with the bead filter is that the presence of large amounts of carbonaceous solids can encourage the growth of heterotrophs at the expense of nitrobacteria (Smith, 2003). Besides, bead filter operation requires high energy consumption and skilful operators. In the fluidized bed filter, filter media is sand that is kept suspended in the influent by the force of water loading upward. The filter velocity is related to the shape, size and density of the particle (Smith, 2003). The biological active surface in to a given volume is greater than any other type of biofilter. It is also self cleaning, tolerant of different type of nutrient loading. However, it is difficult to keep water distributed evenly and the bed depth can be changed when the density of particle increase. A comparison of different types of biofilters in terms of technical and economical aspects is summarized in Table 1. A. Concept design of biofilter for a small scale recirculation aquaculture system To design a biofilter for a recirculation aquaculture system, it is essential to predict the system parameters including fine and dissolved solids, total ammonia nitrogen (TAN), dissolved oxygen and pH. TAN is the vital design parameter for choosing the size and type of biological filter. Mass balance is analysed to determine the rate of feed intake and digestion in the aquaculture system. Mass balance approach is adopted to estimate oxygen consumption and ammonia production (Wheaton et al., 1994). There are plenty of options of filter media to be selected for biological filtration. The filter media

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ranges from sand, rocks, carbon to synthetic materials such as plastics. The selection of the media is based on the specific area, cost, availability and weight per unit. Sand and rock are cheap and easily available but they are quite heavy per unit volume. They are usually used for fluidized bed because of its small diameter, high specific area and resistance to water flow rate. Plastic media has high specific area, light weight but is expensive and can be degradable in direct sunlight. They are generally used for rotating contactors due to their lightness. For trickling and submerged filters, there is no special requirement so that the media can be varied from sand, activated carbon to plastics depending on the availability and cost. The criteria for choosing filter media includes the price for the low largest surface area and high specific surface area, low weight, high mechanical strength, flexibility to different vessel shape, low energy requirement and low maintenance cost. The void fraction of filter media for aquaculture application should be greater 90% (Smith, 2003). Lupatsch et al.(1998) designed a model to calculate the waste production from sea cage culture by measuring nitrogen and phosphorous level at various sites in the system. The Fisheries Western Australia (2004) has developed a waste output model to predict amount, composition of waste from the recirculation system. In this model, the required input data consists of fish species, feed type, cost, initial fish weight, days, temperature and number of fish. The information is essential because each species has specific metabolic rate and it varies at different development stages. To design a biofilter for aquaculture, hydraulic loading rate is determined based on the type of the biological filtration. For trickling and submerged filter, hydraulic loading rate is designed at maximum loading rate that do not scour biomass off the media while for fluidised bed, the hydraulic loading rate is set to keep the media in the filter. B. Design of tricking biofilter for Barramundi (Lates calcarifer) cukture: A sample design calculation

Table 2 Characteristics of the Barramundi culture (Fisheries

NSW, 2004 and Fisheries WA, 2004).

The characteristics of the barramundi culture in New South Wales (NSW) and Western Australia (WA) are summarised in Table 2. Based on the W.A. Fisheries waste output Model (Fisheries W.A., 2004), the waste production of the aquaculture system including carbon, TAN and phosphorous are estimated in Table 3. Oxygen consumption for fish respiration, nitrification and carbonaceous BOD and ammonia production were also estimated by using a mass balance approach.

Table 3 The estimated parameters for biofilter design at the

Barramundi culture (Fisheries NSW, 2004 and Fisheries WA, 2004).

In this system, the operation conditions were assumed steady with the pump capacity at 600 L/minute or 865m3/day, hydraulic loading rate about 100m3/m2.day, pH at 7 and temperature at 280C. The filter media selected for designing is Bio Ball produced by Aquatic Eco systems Inc. The media has a diameter of 25 mm and a specific surface area of 320m2/ m3. Bio Ball is selected because it is light and easily available. For this system design, the ammonia removal rate is assumed at 0.25g TAN/m2day. This assumption was based on the average of the average of the gathered trickling filter data from previous studies (Twarowska et al, 1997; Lekang et al, 1999 and Shnel et al, 2002). The system design is summarized in Table 4 and Figure 2.

Table 4 System design of trickling biofilter for Barramundi

(Lates calcarifer) culture (modified from Wong, 2004)

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Figure 2 Trickling biofilter for Barramundi (Lates calcarifer)

culture (Wong, 2004)Conclusion

Recirculation aquaculture systems have great potential to produce aquatic products under controlled conditions. The most important factor for the operation of an aquaculture system is quality control of feed water. Biofilter has been proved to be an effective system in treating water in an economical manner. The characteristics of the aquaculture system such as its size, ammonia concentration, oxygen consumption, etc. play a major role in selecting and designing a suitable biofilter. The design of the barramundi aquaculture system based on the WA Fisheries waste output model and the mass balance approach. This design was based on the need of ammonia removal to meet the standard of water quality for recirculation system.

REFERENCES [1] Australian and New Zealand Environment and Conservation

Council (2000). Guidelines for Fresh and Marine Water Quality. Chapter 4. Vol 1. ANZECC and ARMCANZ.

[2] Australian Bureau of Agriculture and Resource Economics and Fisheries Research and Development Corporation (2004). Australian Fisheries Statistics 2003. ABARE

[3] Chen, S., Stechey, D. Malone, R. F., (1994). Suspended Solids Control in Recirculation Aquaculture Systems. Aquaculture Water Reuse Systems: Engineering Design and Management. 3rd ed. Elsevier.

[4] Fisheries N.S.W.(2004). Fisheries N.S.W. website. Available at http://www.fisheries.nsw.gov.au. [Accessed on 11/06/2004]

[5] Fisheries W.A.(2004). Government of Western Australia. Available at

[6] http://www.fisheries.nsw.gov.au. [Accessed on 11/06/2004] [7] LaDon, S.(1992). A Basic Overview of Aquaculture History

- Water Quality - Types of aquaculture - Production Methods. Purdue University. West Lafaette. IN

[8] Lekang, Odd-Ivar, Kleppe, Helge (1999) Efficiency of nitrification in tricking filters using different filter media. Aquacultural Engineering. Elsevier.

[9] Lupatsch, Ingrid, Kissil, George (1998). Predicting aquaculture was from gilthead sea bream culture using a nutritional approach. Aquaculture Engineering, Elsevier.

[10] Shnel N., Barak Y., Ezer T., Dafni Z., Rijn J. V. (2002). Design and performance of a zero discharge tilapia recirculation system. Aquacultural Engineering. Elsevier.

[11] Smith, M. (2003). Biological filters for Aquaculture, L.S. Enterprises, USA.

[12] Twarowska J. G., Westerman P. W., Losordo T. M. (1997). Water treatment and waste characterization evaluation of an intensive recirculation fish production system. Aquacultural Engineering. Elsevier

[13] Wheaton F.W., Hochheimer J. n. Kiser G.E., Malone R. F., Krones M. J., Libey G. S. and Easter C.C. (1994). Nitrification Filter Design Methods. Aquaculture water reuse systems: Engineering Design and Management, 3rd ed. Elsevier.