On the Aquaponic Corner section of our Journal

The Editorial explains why we felt it is important to dedicate a section of the journal to aquaponics, the new, emerging food production technology

Influence of pH change on the phosphorus cycle in aquaponics

In fish farming, large amounts of phosphorus (P) are accumulating in the discharge, which on one side poses a problem due to eutrophication potential, but on the other side opens a chance for recycling of this critically limiting nutrient. In aquaponics (AP), which is the combined cultivation of fish (aquaculture) and plants (hydroponic) in one water cycle, plants assimilate P present in aquaculture discharge. The aim of this study was to investigate the P-cycling in aquaponic in order to be able to further optimise P utilisation. For this, the effect of pH manipulation on the system was examined. Three replicates of semi-commercial size aquaponic systems, stocked with Nile tilapia (Oreochromis niloticus), and planted with lettuce (Salanova® Batavia) were monitored from 22th September to 8th November 2017. The pH was adjusted to 6.0±0.2 by adding acid (HCl) during weeks 1 and 2, and to 7.3±0.3 by adding bases (KOH and Ca(OH)2) during weeks 3 and 4. Ortho-P and total-P from different sampling points in the system (system water, sludge, and deposits) were analysed. In addition, biomass production of fish and lettuce, and its nutrient content was compared between the triplicates. The P balance showed that 41% and 8% of the total P inputs provided by feed and water were absorbed by fish and plants, respectively. 27% of P accumulated in the system water, and 24% in form of deposits (biofilm on sump and fish tank surface and deposits on digester heater). Furthermore, digested sludge contained more ortho-P (14-55% of total-P) than fresh sludge (5-10% of total-P). In addition, around 90% of total-P was present as ortho-P in a system water. The ortho-P concentrations after the manipulations of pH in the aquaponic system water surprisingly increased with increasing pH. This is probably due to the complex dynamics between P and Ca. The established P mass balance identified and quantified several P pools, demonstrating that aquaponics systems can maximize overall P utilization if a digester is included into the loop

Redefining ecological engineering in the context of circular economy and sustainable development

In the past decades, the search for a more sustainable way of global development has increased in importance in international politics and economy. A driving force is the continuing degradation of the environment in many areas of the world, often caused or accelerated by population growth and climate change. Sustainable development is seen as key approach to mitigate these processes. It has been defined as “development that meets the needs of the present without compromising the ability of future generations to meet their own needs.” But how can this ambitious goal be achieved in the light of numerous global challenges? Engineering is a very influential human practice and must be addressed in this context. Engineers are crucially involved in design and construction of our built environment and thus in shaping almost its entire development. However, when designing a solution for a given problem, effects caused outside of the system borders are often not considered. If this is combined with a narrowly confined linear problem-solving approach, it is inherently prone to create new environmental challenges. We postulate that the development of a new design paradigm for engineering must be part of the progress towards sustainable development. We think that this new paradigm needs to integrate a sound understanding of ecological principles, processes, and interdependencies as well as thorough system thinking. We call this ecology-inspired approach to engineering “ecological engineering” and redefine it as follows: Ecological Engineering integrates ecological principles, processes, and organisms with existing engineering practice to a holistic approach for problem-solving. In this paper, we explore the historical development of earlier definitions of Ecological Engineering in the light of their underlying value systems. Based on this analysis, we propose a new conceptual approach for Ecological Engineering and define seven principles that point the way towards a future label that can be conferred to Good Ecological Engineering Practice

Importance of nickel as a micronutrient in aquaponic systems : some theoretical considerations

This Note paper calls the attention to the important role the microelement nickel plays is the decomposition of urea in aquaponic systems. Since fish feeds do not contain nickel (it is not included in the list of micronutrients essential to fish growth and development) trace amounts of its soluble salts or complexes need to be added to aquaponic systems in order to achieve the systems' stable operation

Global trends and current status of commercial urban rooftop farming

The aim of this study was to analyze current practices in commercial urban rooftop farming (URF). In recent years, URF has been experiencing increasing popularity. It is a practice that is well-suited to enhancing food security in cities and reducing the environmental impact that results from long transportation distances that are common in conventional agriculture. To date, most URF initiatives have been motivated by social and educational factors rather than the aim of creating large sustainable food production systems in cities. The commercial operation of urban rooftop farms, should they become profitable, is likely to attract notable private investment, allowing a significant level of high quality urban food production to be achieved. There is a reasonable amount of literature available on urban farming that deals with its potential, and its limitations. However, it does not focus on commercial operations. In contrast to other surveys and theoretical papers, this study of URF focuses on large and commercial operations. The analysis showed that commercial URFs can be grouped into two main types: Firstly, hydroponic systems in greenhouses where mostly leafy greens, tomatoes, and herbs are grown; secondly, soil-based open-air farms that grow a large variety of vegetables. Hydroponics is frequently seen as the key technology for commercial urban food production. While the technology is not in and of itself sustainable, hydroponic farms often make an effort to implement environmentally friendly technologies and methods. However, there is still untapped potential to systemically integrate farms into buildings. The findings of this study identified where future research is needed in order to make URF a widespread sustainable solution

Energy toolbox : framework for the development of a tool for the primary design of zero emission buildings in european and asian cities

This paper discusses the framework for the development of an Energy Toolbox (ETB). The aim of the ETB is to support the design of domestic Zero Emission Buildings (ZEBs), according to the concept of net zero-energy buildings during the early architectural design and planning phases. The ETB concept is based on the calculation of the energy demand for heating, cooling, lighting, and appliances. Based on a building’s energy demand, technologies for the onsite conversion and production of the specific forms and quantities of final and primary energy by means of renewable energy carriers can be identified. The calculations of the ETB are based on the building envelope properties of a primary building design, as well as the physical and climate parameters required for the calculation of heat transfer coefficients, heat gains, and heat losses. The ETB enables the selection and rough dimensioning of technologies and systems to meet, and, wherever possible, reduce the thermal and electric energy demand of a building. The technologies included comprise green facades, adaptable dynamic lighting, shading devices, heat pumps, photovoltaic generators, solar thermal collectors, adiabatic cooling, and thermal storage. The ETB facilitates the balancing of the energy consumption and the production of renewable energies of a primary building design

Physiological responses of carp (Cyprinus carpio L.) to dietary exposure to zearalenone (ZEN)

Zearalenone (ZEN) is a frequent contaminant of animal feeds, but systemic effects on fish and possible metabolic costs have not yet been investigated. In order to fill this gap a feeding trial with juvenile carp was conducted. The fish were fed ZEN-contaminated diets at three concentrations (low: 332 μg kg−1, medium: 621 μg kg−1, and high: 797 μg kg−1 final feed, respectively) for four weeks. Possible reversible effects of ZEN were evaluated by feeding an additional group with the mycotoxin for four weeks period and the  uncontaminated diet for further two weeks. After that possible ZEN effects on enzyme activities in kidney, spleen, liver and muscle tissue were investigated to get an organism-wide aspect of ZEN effects. Most organs appeared to (over)compensate ZEN effects during the exposure to this mycotoxin, which caused metabolic costs. Oxygen consumption increased in fish treated with the two higher ZEN concentrations via the diet. The differences between the treatments persisted also after the recovery phase of two weeks. Thus, the present study provided evidence of effects of ZEN on carbohydrate metabolism, lipid peroxidation in organs and metabolic oxygen demand. This is the first evidence for increased metabolic costs in a fish species due to exposure to the mycotoxin ZEN

Wastewater treatment in the urban environment

Constructed wetlands are a valid option for wastewater treatment even in urban areas. In the city, they can be implemented in roof tops, abandoned industrial areas, vertical surfaces of buildings, backyards, porches and public parks. In the suburbs, greywater can be treated in private gardens and reused for irrigation. The performance and control restraints often found disappointing in nature-based systems have been overcome in the past two decades: current systems achieve effluent qualities similar to conventional sewage treatment plants. With area requirements expected to come down to 2.0 m2 per p.e. they would need only two or three times more space. To the core task of treating wastewater they add valuable ecosystem services like micro-climate regulation, rainwater retention, production of renewable energy and/or food, air filtering, noise reduction and recreational values as biotopes with flora and fauna. They represent a new philosophy of dealing with wastes: recycling of nutrients from a valuable resource instead of mere disposal. The new concepts of closing loops call for a more integrated approach represented by the ecological engineer. With its expertise in landscape design and plant usage, horticulture is a key science to promote ecological engineering

Nutrient management in aquaponics : comparison of three approaches for cultivating lettuce, mint and mushroom herb

Nutrients that are contained in aquaculture effluent may not supply sufficient levels of nutrients for proper plant development and growth in hydroponics; therefore, they need to be supplemented. To determine the required level of supplementation, three identical aquaponic systems (A, B, and C) and one hydroponic system (D) were stocked with lettuce, mint, and mushroom herbs. The aquaponic systems were stocked with Nile tilapia. System A only received nutrients derived from fish feed; system B received nutrients from fish feed as well as weekly supplements of micronutrients and Fe; system C received the same nutrients as B, with weekly supplements of the macronutrients, P and K; in system D, a hydroponic inorganic solution containing N, Ca, and the same nutrients as system C was added weekly. Lettuce achieved the highest yields in system C, mint in system B, and mushroom herb in systems A and B. The present study demonstrated that the nutritional requirements of the mint and mushroom herb make them suitable for aquaponic farming because they require low levels of supplement addition, and hence little management effort, resulting in minimal cost increases. While the addition of supplements accelerated the lettuce growth (Systems B, C), and even surpassed the growth in hydroponic (System C vs. D), the nutritional quality (polyphenols, nitrate content) was better without supplementation