Simulation and assessment of the nitrogen cycle in a constant-head, one pump (CHOP) aquaponics system

Abstract

Aquaponics, or the co-culture of fish and plants, has been widely regarded as a solution to the growing food requirement of an increasingly urban landscape. However, difficulties in scaling up arise particularly for start-up growers due to the lack of reliable models to describe the nutrient balance in an aquaponics set-up. In this study, a comprehensive model for the products of the nitrogen cycle is presented in a constant-head one pump (CHOP) aquaponics assembly in order to have a picture of their concentrations in the system, thereby eliminating expensive trial and error adjustments. The growth rate and rate of waste generation of Nile Tilapia, Oreochromis niloticus (Linnaeus, 1758) was mathematically represented alongside the growth rate and rate of nitrogen assimilation of lettuce (Lactuca sativa L.). The evolution of nitrifying bacteria in the biofilter was also modelled. The condition of high recirculation rates was assumed to eliminate the spatial variation of concentration in small-volume modular tanks. The results of the simulation suggest that a linear propagation of both fish and plant through time will result to a deficiency of nutrients for the plants in the beginning of the fish growing cycle, and an excess of nitrates towards the end. To manage rising nitrate levels, the adoption of a staggered growing system was suggested instead of changing water. Overall, the developed model performed satisfactorily in providing a reference to the grower, and is hoped to be extended to other nutrients as well in the future.

Modeling aquaponics: a review on available models and simulation tools

“…This model uses empirical equations calibrated on South-African data within an accessible dimensioning tool for growers. Pamintuan & Doma (2019) focused on the growth of fish, plants and bacteria and their interactions with nitrogen. They produced a model that assesses the nitrogen cycle in a constant-head, one pump aquaponic system.…”