ReseaRch PaPeR Journal of Agricultural and Marine Sciences Vol. 23 : 52– 57 DOI: 10.24200/jams.vol23iss1pp52-57 Reveived 1 Mar 2018 Accepted 18 May 2018 Integrated aquaculture in arid environments 1Stephen Goddard, 2Fatma S. Al-Abri *1Stephen Goddard, ( ) stephen@waterfarmers.ca Water Farmers, Rue de Libin, Hatrival, Belgium 6870. 2Fatma Saif Al-Abri, Centre of Excellence in Marine Biotechnology, Box 50, Sultan Qaboos University, Al-Khod 123, Sultanate of Oman. Introduction Global population growth, coupled with increas-ing water demands, present a major challenge in the provision of future food security. It has been predicted that by 2050 50% more food will be needed to feed a world population exceeding 9 billion (Godfray et al., 2010). This will necessitate intensification of food production, sustainable practices and more efficient use and protection of natural resources. Aquaculture plays a key role in eliminating hunger, promoting health and creating economic benefits and expanded at an average annual rate of 5.8% in the period 2005-2014, to a total of 73.8 million tonnes (FAO, 2016). Inland aquaculture is a major sector although its development in desert and arid regions faces considerable obstacles, particularly with regard to feed and water supplies. The combined production of fish and vegetable crops in integrated sys- tems, with multiple use of water and other resources, holds the potential to increase food productivity in such regions ( Crespi and Lovatelli, 2011). Aquaponics Whilst aquaponics may have ancient antecedents it was likely first developed in its modern form in the mid- 1970’s by scientists researching methods for treating re- cycled water in fish culture systems (Love et al., 2015). In these studies edible plants, including tomatoes and االستزراع السمكي املائي املتكامل يف البيئات القاحلة ستيفن جودرد¹ وفاطمة العربي² Abstract. Around one third of the globe is classified as desert or arid (<200 mm rain annually) and most such re- gions lack food security. Traditional freshwater aquaculture is often a marginal activity and competes with agriculture for limited water resources. Developing technologies offer new opportunities to increase farm productivity through integration with vegetable production in aquaponic systems and to reduce water requirements through the application of biofloc technology. Aquaponic systems combine aquaculture and hydroponic plant production and are integrated within a re-cycled water system. Fish waste metabolites provide the nutrients for plants grown in soil-less, hydroponic systems. Biofloc fish production systems operate with minimum or zero water exchange. Suspended biofloc particles develop in fish tanks under conditions of full aeration and controlled carbon to nitrogen ratios. They comprise algae, bacteria, protozoa and particulate organic matter held in a loose matrix. They provide in-situ treatment of harmful fish metabolites, are protein rich, contain essential fatty acids, vitamins and minerals and supplement the diets of fil- ter-feeding farmed species. The integration of fish culture with vegetable production provides new opportunities for small and medium enterprises. Integrated farms occupy a small footprint, optimise the use of resources and can be built close to population centres. This paper reviews current developments in aquaponics, including recent research into the incorporation of biofloc technology in aquaponics, against the background of food security needs in arid regions. Keywords: water conservation; food security; aquaponics; bioflocs املســتخلص: يصنــف حــوايل ثلــث الكــرة األرضيــة علــى أهنــا صحــراء قاحلــة او شــحيحة املــاء )>200 مــم مــن االمطــار ســنويا( وتفتقــر معظــم هــذه املناطــق إىل األمــن الغذائــي. غالبــاً مــا يكــون االســتزراع الســمكي التقليــدي للميــاه العذبــة نشــاطاً ويتنافــس مــع الزراعــة حمدوديــة ملــوارد امليــاه. حيــث ان التكنولوجيــا املتقدمــة توفــر فرًصــا جديــدة لزيــادة اإلنتاجيــة الزراعيــة مــن خــال نظــام املتكامــل مــع إنتــاج اخلضــروات يف أنظمــة االســتزراع الســمكي املائــي وتقليــل متطلبــات املــاء مــن خــال تطبيــق التقنيــة احليويــة الــي جتمــع بــن تربيــة األمســاك وإنتــاج النباتــات املائيــة يف نظــام إعــادة تدويــر امليــاه. حيــث اهنــا توفــر مــن خملفــات األمســاك العناصــر املغذيــة للنباتــات الــي تــزرع يف النظــام املائيــة مــن دون تربــة. كمــا ان خملفــات األمســاك املوجــودة يف خــزان األمســاك حتــت ظــروف التهويــة الكاملــة والكربــون املتحكــم فيهــا يتحــول إىل عنصــر النيرتوجــن. وكمــا ان الطحالــب والبكترييــا والكائنــات األوليــات واجلســيمات للمــواد العضويــة املوجــودة يف خــزان األمســاك تنتــج خملفــات ســامه وغنيــة بالربوتــن حيــث اهنــا تتحــول هــذه املخلفــات إىل مســاد مغــذي للنباتــات وهــذا ممــا يوفــر مثــن التســميد كمــا ان النباتــات تنقــي امليــاه مــن خملفــات األمســاك الــي قــد تضــر هبــا، حيــث اهنــا حتتــوي علــى األمحــاض الدهنيــة األساســية والفيتامينــات واملعــادن املتكاملــة يف النظــام الغذائــي لتغذيــة النباتــات. كمــا ان هــذا النظــام يعــد متكامــل الــذي يدمــج بــن تربيــة األمســاك وإنتــاج اخلضــروات ويوفــر فرًصــا جديــدة للمؤسســات الصغــرية واملتوســطة. ويشــجع هــذا النظــام علــى اســتغال املســاحات الصغــرية والــي ميكــن بناؤهــا بالقــرب مــن اجملمعــات الســكانية. تســتعرض هــذه الورقــة التطــورات احلاليــة واملســتجدات يف النظــام االســتزراع الســمكي مــع النباتــات، مبــا يف ذلــك البحــوث األخــرية الــي تدمــج التكنولوجيــا يف االســتزراع الســمكي مــع الزراعــة املائيــة بــدون تربــة، والــذي يتماشــى مــن احتياجــات األمــن الغذائــي يف املناطــق القاحلــة. الكلمات املفتاحية: احملافظة على املاء، االمن الغذائي، الزراعة التكاملية بن األمساك والنبات 53Research Article Goddard, Al-Abri lettuce, were used to remove waste products from carp and tilapia production tanks (Naegel, 1977). Early pi- oneering work on aquaponics was pursued by various university research groups, most noteably the group led by James Rakocy at the University of the Virgin Islands in the USA. Aquaponics combines the benefits of fish production (aquaculture) with the soil-less production of plants (hydroponics) using the same water. It operates within a closed-loop system where fish feed provides most of the nutrients required for healthy plant growth. These nutrients, excreted directly by the fish, or gener- ated by the microbial breakdown of organic wastes, are absorbed by growing plants. Research is generally aimed at refining methods for improved output (Rakocy, 2006). The use of soil-less culture techniques and water re-cycling provide considerable benefits for long-term sustainability (Bernstein, 2013). Water consumption is less than 10% of normal levels for horticultural pro- duction and can be provided from potable supplies or pathogen-free groundwater (Somerville, 2015). There are no direct mineral or fertilizer costs since the primary mineral source is the fish feed provided to support fish growth. Some small additions of alkaline salts, to main- tain a stable, neutral pH and ferrous salts, to maintain the necessary iron content, are the only mineral addi- tives used in aquaponics. The intensive nature of aqua- ponic production greatly reduces the amount of land necessary for commercial production units and there is no requirement for arable land. Water recirculation technology has seen significant progress in recent years with some standard methods emerging and equipment supplies becoming more available and cost efficient (Martins et al., 2010; Bregnballe, 2015). The combina- tion of aquaponics with water recirculation technolo- gy has opened the way for aquaponic developments on large commercial scale. Further possibilities exist to conserve water through the application of biofloc technologies. These are zero or minimum water exchange systems production sys- tems in which the carbon nitrogen ratios are adjusted to provide optimal conditions for the growth of bioflocs: small aggregates (<1 mm) of waste food, fecal material, phytoplankton, zooplankton and bacterial communities (Hargreaves, 2013). In well balanced systems the bacte- rial communities take up the nitrogenous compounds, which are otherwise harmful to fish, and produce micro- bial protein, lipids, vitamins and minerals. Fish produc- tion, using biofloc systems, linked to hydroponic plant production in aquaponic systems holds the potential to minimise water use and to reduce feeding costs through improved food conversion ratios. Initial trials have demonstrated the availability of minerals from bioflocs in integrated fish and vegetable production (Chappell and Brown, 2010) and the potential to develop aquapon- ics, based on fish production in biofloc systems, is being researched, with positive results (Pinho et al., 2017). Figure 1. Al-Arfan Farms, Oman. A commercial aquaponics farm operating in a hot arid environment. The farm is protect- ed by a shade house and the fish unit produces 4-5 tonnes of Nile tilapia each year. A wide variety of vegetables, fruits and culinary herbs are grown throughout the year in a combination of deep water culture and media filled beds. Picture credit: Arvind Venkataraman 54 SQU Journal of Agricultural and Marine Sciences, 2018, Volume 23, Issue 1 Integrated aquaculture in arid environments Vegetable production A wide range of vegetables and fruits are grown in aquaponic systems, including include lettuce, chard, pak choi, spinach, kale, basil, tomatoes, peppers and micro-greens. Three systems are available for hydro- ponic plant production. These are described in detail by Somerville et al., (2014) and are summarised below. Nutrient film systems (NFT) These are based on conventional hydroponic systems in which plants grow in long narrow channels. Water flows down each channel, providing plant roots with water nutrients and oxygen. NFT Systems must also in- clude tanks for settlement of solids and a bio-filter for the breakdown of ammonia. The systems are prone to blockage with circulating organic materials and are less commonly used in aquaponics than deep water culture and media-filled systems. Media-filled systems In these systems crops are produced in shallow grow- beds (50 cm), using media to provide support for root systems. Expanded clay balls or graded gravel are com- monly used. The system is typically operated with a flood and ebb system controlled by a bell siphon, where each bed is filled with nutrient-rich water and drained 2-3 times each hour. The media provides large surface area which promotes biological filtration, reducing ammonia to nitrite and nitrate. The media also provides support to plant root systems and enables relatively tall plants to be grown. All of the organic waste is broken down in the grow beds and worms are often added to enhance the breakdown. The overall productivity of plants is general- ly less than in NFT and floating raft systems, although a greater variety of plants can be grown. Deep water culture systems This method is used for smaller plants such as herbs and salads, which grow floating in a styrofoam raft. The plants are initially contained in small coir pots and re- ceive their necessary minerals from the fish tank via the water which circulates around their exposed roots beneath the floating rafts. The fish are held in a sepa- rate tanks and water from the fish tank circulates con- tinuously through the system. Beneficial bacteria live throughout the system and the extra volume of water in the grow beds provides a buffer for fish, reducing stress and potential water quality problems. Deep water culture and media-bed systems are most commonly used in aquaponics. They may be used sin- gly or in combination. Deep water culture methods are commonly used in large commercial units for the pro- duction of large quantities of mono-crops, such as let- tuce, salad greens and culinary herbs. Fish production A limited range of freshwater fish species is grown in aquaponics. Tilapia (Oreochromis spp) is most common- ly grown since it is hardy, readily available, grows rapidly under optimal conditions and is familiar to consumers (Bernstein, 2013). Other warm-water species include Asian seabass, catfish and carp, including ornamental varieties of koi carp. The volume and value of food fish grown in aquaponics is small in comparison with plant production. Plants reach harvest faster, which permits multiple plantings and have higher value per unit weight than fish. Typically, profits are gained on plant yield rather than fish production and fish are primarily used as a source of bio-available plant nutrients. Water re-use and treatment The essential requirements for treatment of recycled water depend primarily on the plant growing system se- lected. Small scale, media-filled grow beds will remove solids and function as biofilters. In contrast deep water culture systems require additional solids separation and biofiltration. Water flows from the fish tanks in a cycle through solids separation equipment, followed by biofil- ters and then through the plant grow beds. It is then col- lected in a sump and pumped back to the fish tanks. Air, generated by blowers and delivered through fine bubble diffusers, is applied directly in the fish tanks and in deep water culture beds. More efficient oxygenation using ox- ygen generators or stored liquid oxygen is necessary for fish cultured at high stocking densities. Solids removal Separating solids from fish tank effluent is a key part of water management in commercial deep water culture aquaponics. Accumulation of solids in the water can cause irritation and gill damage in most fish species and within the hydroponic system can accumulate around the root systems of growing plants impairing the uptake of water and dissolved nutrients. A range of sizes of sol- id particles are excreted by feeding fish and various sys- tems are available to separate the various solid fractions (Table 1). Settleable and supra-colloidal solids form the bulk of solids excreted by fish and can be removed by grav- itational devices and micro-screens. Circular fish tanks with flat bottoms are generally used in large installations. Water circulates uniformly and centripetal forces trans- port solid wastes to the centre from where they can be Table 1. Solids waste in fish tank effluent Solids type Size (µm) Treatment Dissolved < 0.001 Ozone Colloidal 0.001 – 1 Foam fractionation Supra-colloidal 1 – 100. Screen filter or sand/bead filters Settleable > 100 Swirl filters or radial flow settlers 55Research Article Goddard, Al-Abri separated in a small separate drain pipe from the main flow of cleaner water. Additional suspended solids can then be removed by a combination of swirl separators, radial flow filters or rotating drum filters fitted with mi- cro-screens (40-100 µm), depending on the nature and volume of solids to be removed. Biofiltration The finest particles will pass through separators and micro-screens along with dissolved compounds, such as phosphorus and nitrogen. Nitrogen in the form of nitrite and free ammonia (NH3) is toxic to fish and is oxidised by nitrifying bacteria growing in films on the biofilter surface to harmless nitrate, which is then avail- able for plant growth. Biofilters units are designed to contain as large a surface area as possible to support the growth of bacterial films. Light, plastic media giving a high specific surface area (SSA, m2/m3) is commonly used (Harwati and Jo, 2011). Biofilters can be configured in varioius ways and many designs are currently used in aquaponics (Table 2). The size of biofilters is calculat- ed based on various parameters. These include the total ammonia-nitrogen (TAN) released by the fish, hydraulic loading, water flow rates and the relative surface area of the selected filter media. TAN calculations are based on the nitrogen content of the fish feed, daily food con- sumption, digestibility and nitrogen content of protein. Calculating biofilter size should also take into account the available surface areas of the grow beds and styro- foam floats which will be in contact with water and will also support the growth of bacterial films. Metrics based on feed use are fundamental to aqua- ponics. Determination of the quantity and quality of food used daily are used to calculate both scope of water treatment necessary and the scale of hydroponic plant growth which can be supported by the treated effluent from fish tanks. Routine monitoring of water chemistry is vital to maintain a balanced water re-use system (Colt, 2006). Recycled systems accumulate acidity which must be adjusted by base additions to maintain optimal pH for fish, bacteria and plant growth growing in the same system. Safety Food safety is a critical component of food production and aquaponic farmers should follow codes of good practice and apply biosecurity protocols for both aqua- culture and horticulture components. Food safety and levels of food safety indicator organisms from both pro- duce and water in aquaponic systems have been exam- ined (Chalmers, 2004; Fox et al., 2012; Goddard et al., 2015). The bacterium Escherichia coli is the most widely studied potential contaminant in aquaponics. This bac- terium is found in the intestines of warm-blooded an- imals, including birds and cattle, and has been used in developing human health-based regulatory standards as a common indicator of fecal contamination and micro- bial water quality in agricultural water systems. Indica- tor microbes and pathogenic bacteria, such as E. coli and Salmonella spp., if present in aquaponic systems, most probably originate from warm-blooded animals, such as birds, since these enteric bacteria are transient in fish gut microflora (Sugita et al., 1996). As in all crop pro- duction systems cross-contamination is possible, but the risk in aquaponics is greatly reduced when compared with field crops (Sirsat and Neal, 2013). Studies from Oman (Goddard et al., 2015), USA (Fox et al., 2012) and Canada (Chalmers, 2004) have reported negative tests across numerous aquaponic farms for E. coli and Salmo- nella spp. Biofloc farming systems The application of biofloc technology in intensive aqua- culture is in its early stages (Avinmelech, 2007). The technology is based on waste nutrient recycling, par- ticularly nitrogen into microbial biomass. This biomass can be used directly by filter feeding species such as tila- pia, carp, catfish, marine shrimp and freshwater prawns (Bossier and Ekasar, 2017). On a dry matter basis, micro- bial biomass has been shown to contain 20-45% crude Table 2. Characteristics of 4 biofilter types used in aquaponic systems Type SSA (m2/m3) Characteristics Trickle filter 200 Water enters from an overhead spray pipe and cascades through a media column (e.g. corrugated plastic sheets) where nitrification occurs. Relatively inexpensive and simple to construct and operate. They self-aerate and de-gas excess CO2 Rotating bio-con- tactor 200 Filter media comprises circular plates or discs attached to a horizontal shaft. The media is half submerged in the fish tank or a separate container. As the filter rotates the media is alternately submerged and exposed to the air. Passive aeration and CO2 degassing occurs and head loss is low. Simple to operate and can powered by a small motor or air-lift. Higher initial purchase and maintenance cost than trickle filters but more compact. Moving bed bio- film reactor 500 Filter media (small plastic spheres with surface sculpting) is held in an open tank (50% water and 50% media). The bottom of the tank is fitted with an air distribution system designed to give continuous turnover and aeration of the submerged media. Head loss is low. Various adaptations of this filter are commonly used in aquaponics on both small and large-scale. Bead filter 3000 Filter media (tiny glass beads) is held in a pressurised vessel through which the water is pumped. Combines solids removal and nitrification. Automatic backwash. Compact but high initial cost. 56 SQU Journal of Agricultural and Marine Sciences, 2018, Volume 23, Issue 1 Integrated aquaculture in arid environments protein, 1-5% lipids and various bioactive compounds including essential fatty acids, carotenoids, vitamins and minerals (Kuhn et al., 2009). The availability of in situ nutrients has opened the way for reformulation of spe- cial aquafeeds for use in biofloc systems. Protein content can be reduced and fish meals can be replaced with plant meals. This both improves sustainability and reduces cost (Martinez-Cordova et al., 2015). In practice biofloc tanks or ponds must be continuously mixed and aerated and the carbon nitrogen ratio (C:N) carefully maintained (12-20:1) to support the formation and stabilisation of a heterotrophic microbial community (Perez-Fuentes et al., 2016). Carbon content is balanced using available carbohydrate sources such as molasses or grain pellets. Total suspended solids content is monitored through- out the fish production cycle and maintained at optimal levels of 100-300 ppm. Excess biomass can be harvested and processed into feed ingredients (Kuhn et al., 2009). Biofloc farming systems operating with zero or mini- mum water exchange offer greatly enhanced biosecurity, which is particularly valuable for shrimp farmers in the control of transmissable viral diseases. The role of nat- ural probiotics and immunostimulants on survival and growth have also been reported from studies on the mi- crobial ecology of bioflocs (Rani et al., 2017) Planning and economics A detailed review of planning, construction, operation and economics of small-scale aquaponic farms has been provided by FAO (Somerville et al., 2014). Capital costs can be high in relation to income and a recent survey suggest that the majority of aquaponic farms operate on small commercial scale (Love et al., 2015). Farm de- sign should be optimised for the targeted production levels and fish species (limited choice) and plant vari- eties (wide choice) should be selected based on local and regional consumer demand and value. Some fail- ures of large projects have been reported where profits could not match the demands of initial investment plans (Somerville et al., 2015). Aquaponics in urban environments is taking the lead in large-scale developments. Disused industrial space, including rooftops, is attracting developments in many European and North American cities. They are typically based on the use of a temperature and light-controlled greenhouse structures designed to support year-round production and incorporate space-saving stacked and vertical horticulture systems (Kyaw and Ng, 2017). Cap- ital and operating costs are high but operators benefit from a large consumer base and demand for organical- ly produced fresh products from local suppliers. Urban projects also play an important role in education and public awareness. Future prospects Aquaponic developments hold great potential to con- tribute to food security and support sustainable devel- opment goals in hot arid and regions. They benefit from efficient water use, high productivity and low environ- mental impact. In these regions costly heating systems and greenhouse structures are not necessary and solar energy can be used to generate electricity supplies for water pumps, aerators and other equipment. This re- duces capital and operating costs and supports the de- velopment of aquaponic enterprises as small or medium enterprises or ever large commercial ventures. Integration of aquaponics with biofloc technologies has the potential to reduce the costs of water treatment, improve feeding efficiency and scale-up fish production. Early research indicates the bio-availability of plant nu- trients in biofloc tanks and ponds. Systems will howev- er require modification for efficient handling of solids waste and excess biofloc. Further potential exists to apply aquaponic tech- niques in arid regions, where salinization of ground water restricts traditional agriculture. 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