Recovery of nutrients from fish sludge in an aquaponic system using biological aerated filters with ceramsite plus lignocellulosic material media

The recovery of nutrients from residual fish sludge in aquaponics could achieve zero solid waste discharge and supplement additional nutrients to hydroponics, thus yielding environmental and economic benefits. In this study, novel biological aerated filters (BAFs) with ceramsite plus different lignocellulosic materials (corn straw, wheat straw, and sawdust) are designed and installed in aquaponic systems. The BAFs performed the fish sludge separation and nutrient conversion in a single equipment without the necessity for backwashing. The potential for nutrient recovery from fish sludge is evaluated by comparing four BAFs filled with different media. The BAF with ceramsite plus sawdust achieves the highest mineralization capacity based on nitrification and dissolved total phosphorus. The average concentrations of N, P, K, Ca, Mg, and S macronutrients reach 12.3%, 11.8%, 4.5%, 26.4%, 22.6%, and 46.0% of those of Hoagland nutrient solution, respectively. The recovered Fe, Mn, and B micronutrients are 10.0%, 12.0%, and 18.0%, respectively, whereas Cu, Zn, and Mo are 1.5, 1.8, and 1.0 times, respectively, of those of Hoagland nutrient solution. The estimated nutrient recoveries of Ca, Mg, and S have good performance efficiencies, followed by K and Cu; those of N, P, Fe, Mn, and Zn have potentials for further improvement. The modified aquaponics with BAFs are proposed for the recovery of both dissolved and solid nutrients.