Physical filtration of nutrients utilizing gravel-based and lightweight expanded clay aggregate (LECA) as growing media in aquaponic recirculation system (ARS)

Abstract

The aquaponic recirculation system (ARS) combined aquaculture and hydroponic systems in a mutually beneficial environment. In this study, African catfish, Clarias gariepinus with Butterhead lettuce, Lactuca sativa were cultivated to evaluate gravel-based media and lightweight extended clay aggregate (LECA) as a physical filtration in the nutrient's removal. The performance of both tested growing media was assessed through the reduction of nutrient concentrations in the circulated water, which were total ammonia nitrogen (TAN), nitrite-nitrogen (NO2--N), nitrate-nitrogen (NO3--N), and phosphorus (PO43--P). Statistically, there were significant differences in the percentage of nutrient removal between gravel-based media and LECA treatment for TAN, NO2--N, NO3--N, and PO43--P. TAN removal efficiency achieved 92.47 ± 1.03% in LECA compared to 61.26 ± 2.69% in gravel-based media. For NO2--N, the removal efficiency was 77.25 ± 1.47% and 22.43 ± 6.84% in LECA and gravel-based media. The removal efficiency of NO3--N on LECA was two times more than gravel-based, 60.03 ± 1.58% and 30.77 ± 1.54%. The removal efficiency of PO43--P was 64.29 ± 1.82% for LECA while 27.43 ± 1.62% for gravel-based media. In addition, L. sativa yield was significantly higher in LECA with 64,961.71 ± 1295.61 g/m² as compared to 31,0582.82 ± 877.07 g/m² in gravel-based media. Significantly higher SGR of C. gariepinus in LECA with 3.94 ± 0.11%/day compared to 3.10 ± 0.12%/day in gravel-based media. LECA is an adsorptive substrate with a high removal capacity for phosphorus and nitrogen in aquaculture wastewater, increase its use as growing media in ARS or hydroponics.