Enhancing nutrient recovery from fish sludge using a modified biological aerated filter with sponge media with extended filtration in aquaponics

An effective strategy for the nutrient recovery from fish sludge in aquaponics is critical for cleaner and sustainable production. The modified biological aerated filter (MBAF) is applied as an effective approach for the collection and conversion of fish sludge to nutrients in one reactor. Nutrient conversion would be synchronized during the filtration of fish sludge if the filtration time is sufficient, which is significant for the nutrient recovery. To test the hypothesis, in this study, modified biological aerated filters filled with polyurethane sponge media were equipped to the fish tank of a pilot aquaponic system to examine the effect of extended filtration time on the nutrient conversion with respective extended filtration time of 11 d (MBAF-1) and 36 d (MBAF-2). The MBAF-2 collected more fish sludge than the MBAF-1 by ca. 57.0%. The duration time of filtration was limited by total ammonia nitrogen in the fish tank. Most of the fish sludge was transformed into soluble nutrients in both MBAFs. In MBAF-2, higher macronutrient and micronutrient concentrations were achieved than that in MBAF-1, especially N and P (4.0 and 2.1 times greater, respectively). MBAF-2 had a high nutrient recovery efficiency (NRE), namely 22.6% for N, 62.1% for P, 17.1% for K, 39.7% for S, 18.5% for Mg and 79.1% for B, respectively, indicating the N and P recoveries in MBAF-2 were 6.1 and 3.0 times of those in MBAF-1, respectively. Based on the results, an optimized aquaponic system with two-stage MBAFs is proposed, and each stage consists of two filter columns to conduct the extended filtration of fish sludge and the nutrient conversion alternately