The Need for Systems Design for Robust Aquaponic Systems in the Urban Environment

Aquaponics – the co-production of fish and plant products – is gaining interest both by entrepreneurs and researchers. This article evaluates both the technical setup as well as the economic potential of aquaponic systems and is aimed at identifying relevant knowledge questions for further improvements. Using system requirements for hydroponic systems and aquaculture, the aquaponic system was compared to a typical Dutch rockwool system. Aquaponics was found to be an improvement on current practices when using Deep Flow Technique (cultivation in a flowing thick water layer), resulting in better nutrient availability for the plants and re-use of nitrate. However, the technical challenges of the direct linkage between the two production systems in terms of needed technology and disease management was found to make the total system suboptimal when compared to conventional practices. The technological advantages of efficiency in use of land and energy and re-use of nutrients were found to be a marginal cost reduction of 1.2%. The article concludes that the added value of aquaponics can be found in the total business concept of producing in an urban environment with direct relationship with consumers. Further improvement of aquaponics can be found in improved disease management of the system – through management or improved design. INTRODUCTION Urban farming creates value through the production of small scale, sustainable and local produce, often in direct interaction with the consumer. Sustainability is achieved through the re-use of waste streams of water, nutrients and energy by combining different (agricultural) activities. A sustainable, applicable and small scale system for such re-use is the combination of fish production in Recirculating Aquaculture Systems (RAS) and horticulture – so called Aquaponics. For professional aquaponics to take off in Europe the production systems need to have added value, be robust and easy to use. Research has focused on plant aspects (nutrients and quality; Pantanella et al., 2012) and fish production (densities, diseases) and technology. But less on the business rationale and design structure. However, designing for such complex systems requires a systematic approach, where an analysis of functions and quantified requirements is used to select and improve on the technical lay-out. Functions and requirements are based on insights and needs from both researchers and experts as well as users and stakeholders – in the case of urban farming city planners and the general public. However, such analysis has only recently been developed for both hydroponic systems and aquaculture, but not for the combination of the two nor the application in an urban setting. This paper describes the system requirements for both aquaculture as well as horticulture that would apply for aquaponics in an urban environment. SYSTEM TO BEAT For aquaponics to be developed in the northwestern European context, it will have to compete with the current food system for fresh produce. The development of the horticultural cluster in the North-West of Europe has resulted in the availability of fresh produce at relatively low price at close proximity. The logistical systems allow for fresh stock being delivered multiple times a day at local supermarkets. Likewise the logistical Proc. IS on Soilless Cultivation Eds.: Weimin Zhu and Qiansheng Li Acta Hort. 1004, ISHS 2013 72 hub of harbours like Rotterdam, Antwerp and Hamburg make it possible to supply mainland Europe with frozen fish from all over the world, while marine fish is caught locally or imported through these same harbours. Development of aquaculture in RAS has been slow and difficult (Martins et al., 2010). Table 1 showed that at high production levels the current agricultural system is able to produce at low costs. Largest contributors to the costs in horticulture are the costs for energy, labour and investment (land and facilities). PROMISE OF AQUAPONICS In order for aquaponics to be a profitable solution to current northern European agriculture and aquaculture sector, the system has to be better at reducing costs and/or delivering added value. Where cost reduction is relatively easy to calculate, value adding can be viewed as a product-characteristic (taste, appearance, traceability), a logistical benefit (volume, just in time, local) or a (paid) societal value. On-farm integration of aquaculture with other agriculture production systems has a long tradition in Asia (Prein, 2002) and comes world-wide in many different varieties. Recently, the application of Integrated Multi Trophic Aquaculture (IMTA) in modern fish farming is studied seriously (Bunting and Spighel, 2009). Aquaculture in closed systems (RAS) has developed strongly during the last decades (Martins et al., 2010). This production system is ideally suited for urban environments (Costa Pierce, 2005). RAS produces a relatively small flow of nutrient rich effluent which can technically be utilised in a hydroponics production system. From an environmental point of view, the integrated system is seen as more sustainable through the re-use of nutrients (N and P), the higher efficiency in use of land and energy. Technically it promises a local, robust and smarttech solution to fresh produce, while economically it is presented as a viable system (Rakocy, 1999; Rupasinghe and Kennedy, 2010; Seawright et al., 1998). DESIGN APPROACH Aquaponic systems need to meet well the requirements of both the crops as the fish, and the added requirements for joining the two. Using design approaches earlier developed for production systems (Kroonenberg and van den Siers, 1999; Van Henten et al., 2006) first drafts of systems can be made and evaluated on paper. These approaches apply a systematic definition of requirements, functions and quantified evaluation criteria for the system. Using these quantified criteria a design can be evaluated. For the separate systems of horticulture and aquaculture as well as the combination of the two aspects, crucial system requirements and evaluation criteria are given in Table 2. The requirements and criteria are a set of optimal and critical values for production factors for both crop and fish. The table shows quantified values such as minimal O2-concentrations in the water basins as well as indicators that are species specific and require further quantification. Optimisation of aquaponic systems has been achieved over the past years through 1) applying Deep Flow Technique (DFT – systems with a water level generally more than 5 cm deep, with the water kept in circulation, while plants float on the water in styrofoam plates or otherwise held in position) for the crop production and 2) availability of other fish species apart from tilapia. Deep flow systems buffer imbalance in the nutrient solution through the larger quantity of nutrient solution per plant than in other systems. The roots are replenished continuously as opposed to substrate systems where refreshment of the root zone is limited by the water holding capacity of the substrate. Because of the ability of delivering high yields using a sub-optimal nutrient solution, the development of Deep Flow systems has been more beneficial for aquaponic systems than conventional hydroponic systems. Recent findings in the positive effect of keeping the plant base above the water level (made commercial through concepts like ‘Dry Hydroponics’; Cultivitation Systems, 2012) make it possible for more herbaceous plants to grow on deep flow. Optimisation of crop rotation has been shown to be an important tool in nutrient utilisation (Adler et al., 2003).