Real-time monitoring and control of an aquaponic system to ensure sustainability

Abstract

In recent years, climate change awareness, with resultant potential dwindling water resources and strain on existing food production infrastructure, has grown. Establishing a sound scientific basis for the creation, operation, and maintenance of alternative sustainable food production methodologies is thus essential. The ‘closed system’ nature of aquaponics promises high yield versus surface area as compared to traditional agriculture and is inherently sustainable.

Since aquaponics systems may be set up in cities and suburbs, there is potential to establish food ‘cells’ that benefit the population in the immediate area. Such benefits include fresh produce, reduced storage, pollution and transportation costs, and increased employment and food security. In a climate that features freezing winter temperatures (such as in Bloemfontein, South Africa), sustainable thermal supplementation is required to maintain the viability of aquaponics systems. Monitoring and controlling thermal supplementation in real-time is necessary to mitigate thermal losses and prevent bio-filter micro-biota mortality related to extreme cold winter temperatures and to ensure sustainability.

The dynamic interrelated nature of thermal interaction between aquaponics subsystems and the large volume of water typically present in main aquaponics reservoirs further inform the necessity of implementing such a monitoring and control system. Presenting the aquaponics system and subsystems’ thermal interaction in a conceptually simplified manner, which may be applied to other aquaponics systems and topologies, also promotes integration of aquaponics into the African agricultural paradigm. The subsystem contributions, as conceptually described via water mass-flow energy transfer, may be readily quantified by differential temperature measurement and volumetric flow determination.

Furthermore, presenting a grid-equivalent energy- purchase estimation methodology to maintain sustainability potentially motivates entrepreneurs and investors by offering investment confidence, thus further incentivising adoption of aquaponics as technology. This study was conducted during an unusually severe 2020 winter season in Bloemfontein, South Africa, and fortuitous occurrence of uncommonly closely spaced cold fronts enables challenging the hypothesis expounded in the presented methodology. Offsetting midwinter temperature loss in the 42 kl main aquaponic reservoir, as further detailed in Annexure F, a 1.3°C temperature loss mitigation over a period of three days was realised. Employing the daily temperature recovery slope metric (as more examined in Annexure G), an average positive temperature recovery slope of 0.278°C was noted. The real-time nature of the online data as collected by the monitoring and control system additionally promotes adoption of such electronically enhanced aquaponics systems into the concept of ‘Sustainable Smart Cities’. The method presented, utilising the concept of mass-flow energy transfer to quantify the subsystem energy contribution to the main aquaponics reservoir, is inherently scalable and may be readily incorporated for use in different aquaponics system topologies. As such, it represents a useful tool for further research in the field and compares favourably against the established epistemological approach of using a thermodynamic description, which is complex and computationally taxing, and can be difficult to realise for systems also containing a biological component.