Towards understanding the dynamic behaviour of bioflocs in a fish tank culture: Integration of fish growth and activated sludge modelling

Biofloc can improve the nutrient use efficiency of an aquaculture system. However, knowledge of the dynamic behaviour of biofloc related to the nutrient concentration in the water is limited. This study combined the fish growth model with the activated sludge model (ASM), later called fish-ASM, to understand the dynamic behaviour of biofloc in Nile tilapia culture. Fish were fed two types of diets that differ in fiber content. One of the diet contains three times higher fiber, which was formulated by incorporating more non-starch-polysaccharides (NSP). NSP is expected to increase carbon content in the water and promote more biofloc growth. Initial model parameter values were gained from experiments and ASM number 1. In fish-ASM, waste comes from uneaten feed, fish faeces, decay of heterotrophic and autotrophic biomass, and fish gill excretion (ammonia). Heterotrophic and autotrophic biomass then utilize the waste as substrates for their growth and part of the biomass is consumed by fish as natural food. The main model outputs in this study are hourly dynamics of fish, biofloc, and nitrogen in water. After trial and error calibration process, the model was fit to the fish, biofloc, and nitrogen dynamics of the lower fiber diet datasets with relative mean square error of 3 %-34 % to the corresponding average observations. However, future improvement was needed in the higher fiber diet simulation, especially related to biofloc and ammonia dynamics. The study shows that the development of biofloc was strongly influenced by organic matter availability. • An activated sludge model (ASM) was coupled to a fish growth model (fish-ASM). • The effect of dietary fiber content on activated sludge formation was simulated. • The model best predicted the biofloc formation in a system with a fiber-poor diet. • Model improvement is needed to predict biofloc dynamics for a fiber-rich diet. • Biofloc development was strongly influenced by organic waste availability.