PHOSPHORUS DYNAMICS MODELING AND MASS BALANCE IN AQUAPONICS

Aquacultural effluents are known to be rich in phosphorus (P) and nitrogen (N), being a growing concern worldwide due to their potential of environmental pollution. Hence integrating aquaculture with agriculture, e.g. aquaponics, has potential to enhance nutrient and water use efficiency and overall environmental sustainability. Little is known about the dynamics and mass balance of P in aquaponics. It is important to understand nutrient absorption dynamics in order to adapt inputs to extraction rates. This trial was conducted to quantify a P flow and a P budget by using a nutrient mass balance equation and evaluate P production, loading, and removal efficiency of hydroponic lettuce integrated with tilapia aquaculture in a NFT-aquaponics system.

15 tilapia juveniles (20g) and four 15-day-old lettuce seedlings comprised each aquaponics experimental unit. Fish were fed 1% of their biomass per day. At days 0, 7, 14, 21 and 28 after transplanting, water samples were taken from each biofilter to determine reactive and total concentration of P. Lettuce, fish and feed samples were oven dried and ground for P content analysis. The model was validated by comparing simulated to observed values of dissolved P over time. The linear regression equations between simulated and measured values were compared with the 1:1 line for statistically significant differences (p < 0.05) in slope and intercept values. The adequacy of the model was determined by testing if intercept equals zero and slope equals one separately using the one sample Student T-test. Comparison of simulated and measured values of dissolved P dynamics (Fig. 1) showed a good fit around the 1:1 line with the slope (b = 1.005) and intercept values (a = 0.0189) being not statistically different (p > 0.05) from 1.0 and 0, respectively. The assimilation of P in the fish and plant components comprised 74.2% of the total P input, indicating high P utilization by the system (Fig. 2).