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

Microbial diversity across compartments in an aquaponic system and its connection to the nitrogen cycle

Aquaponics combines hydroponic crop production with recirculating aquaculture. These systems comprise various compartments (fish tank, biofilter, sump, hydroponic table, radial flow settler and anaerobic digester), each with their own specific environmental pressures, which trigger the formation of unique microbial communities. Triplicated aquaponic systems were used to investigate the microbial community composition during three lettuce growing cycles. The sampling of individual compartments allowed community patterns to be generated using amplicon sequencing of bacterial and archaeal 16S rRNA genes. Nitrifying bacteria were identified in the hydroponic compartments, indicating that these compartments may play a larger role than previously thought in the system's nitrogen cycle. In addition to the observed temporal changes in community compositions within the anaerobic compartment, more archaeal reads were obtained from sludge samples than from the aerobic part of the system. Lower bacterial diversity was observed in fresh fish feces, where a highly discrete gut flora composition was seen. Finally, the most pronounced differences in microbial community compositions were observed between the aerobic and anaerobic loops of the system, with unique bacterial compositions in each individual compartment

Bioponics—An Organic Closed-Loop Soilless Cultivation System: Yields and Characteristics Compared to Hydroponics and Soil Cultivation

Sustainable food production has become increasingly important. Soilless cultivation systems offer several advantages, such as water and nutrient use efficiency, and can be implemented where traditional agriculture is impossible. Bioponic systems use locally or regionally available nutrient sources from organic waste streams (either fluid or solid) and can thus contribute to closing nutrient cycles locally. Bioponics harnesses the metabolic processes of microorganisms which release nutrients from organic matter. This study aimed to set up a bioponic system, by using biogas digestate concentrate and biochar as nutrient sources, and promoting nutrient release from the organic sources by including a biofilter in the system. The development of water quality, plant growth, and quality was monitored extensively. In addition, the influence of either the fungal biocontrol agent Trichoderma atrobrunneum or UV-C treatment of the nutrient solution on plant health and growth was investigated. Three cultivation cycles with Lactuca sativa (“HAWKING” Salanova®) in bioponic (BP), hydroponic (HP), and soil (SO) cultivation were performed. The study showed that healthy lettuces could be produced in BP systems, using a biogas digestate concentrate and biochar as nutrient sources, despite salt accumulation in the nutrient solution. In plant sap analyses, lettuces cultivated in BP systems contained less nitrate but more ammonium and chloride. The yield of the lettuces grown in the BP systems was intermediate, compared to the HP and the SO. The fungus, T. atrobrunneum, strain, T720, survived in soil and soilless cultivation systems. Compared to the HP and the SO systems, the shoot height of lettuces grown in the BP system, with the application of Trichoderma, was significantly increased. In SO systems with Trichoderma application, a significantly higher chlorophyll and flavonoid content, but significantly lower shoot height was observed. The fresh weight of lettuce roots was significantly higher in HP systems with Trichoderma treatment. Cultivating plants by using organic waste streams requires commitment and experience from producers. In BP systems, a biofilter (either within the system or externally, to increase nutrient levels) can help to rapidly convert the ammonium-rich fertilizer to plant-available nutrients. Unlike conventional HP systems, in BP systems, nutrients are released slowly over time, requiring close monitoring and adjustments. In conclusion, healthy lettuces for human consumption can be produced in BP systems, and the application of the biocontrol agent used has some beneficial influence on plant growth

Lessons learned from introducing aquaponics to higher education curricula

Aquaponics is an innovative and sustainable food production technology which has the potential to make a significant contribution to 21st century food systems, especially if there is an adequately trained workforce. In this chapter we review the efforts of an international consortium to develop a curriculum for teaching the basics of aquaponics to final year undergraduates and Masters students. As a nature-based solution which addresses a number of socio-environmental challenges, including food and water security, water pollution, human health, and climate change, aquaponics combines aquaculture and horticulture in an ecologically balanced closed-loop system. Teaching aquaponics promotes ecological literacy among students, thereby enabling future professionals of various careers whose activities are affected by – and have consequences for – environmental issues, and provides a pathway for introducing the concepts of sustainable development and the circular economy to higher education curricula

Microbial diversity across compartments in an aquaponic system and its connection to the nitrogen cycle

Aquaponics combines hydroponic crop production with recirculating aquaculture. These systems comprise various compartments (fish tank, biofilter, sump, hydroponic table, radial flow settler and anaerobic digester), each with their own specific environmental pressures, which trigger the formation of unique microbial communities. Triplicated aquaponic systems were used to investigate the microbial community composition during three lettuce growing cycles. The sampling of individual compartments allowed community patterns to be generated using amplicon sequencing of bacterial and archaeal 16S rRNA genes. Nitrifying bacteria were identified in the hydroponic compartments, indicating that these compartments may play a larger role than previously thought in the system's nitrogen cycle. In addition to the observed temporal changes in community compositions within the anaerobic compartment, more archaeal reads were obtained from sludge samples than from the aerobic part of the system. Lower bacterial diversity was observed in fresh fish feces, where a highly discrete gut flora composition was seen. Finally, the most pronounced differences in microbial community compositions were observed between the aerobic and anaerobic loops of the system, with unique bacterial compositions in each individual compartment.ISSN:0048-9697ISSN:1879-102