Novel maricultural-solid-waste derived biochar for removing eutrophic nutrients and enrofloxacin: Property, mechanism, and application assessment

Land-based seawater aquaculture accompanied by high stocking density usually involves producing excess eutrophic nutrients, residual baits, excrement, and antibiotics. Because of limited technology and salinity, proper and efficient treatment of these wastes is still an unsolved issue. In this study, the feasibility of maricultural fish residual bait and excrement-derived biochar as water pollutant remover and saline–alkaline soil amendment were firstly assessed. The biochar was pyrolyzed at 300, 500, 700, 800, 900 ℃ (marked as BC300, BC500, BC700, BC800, BC900) and modified by zirconium or iron (BC700-Zr or BC700-Fe). BC700-Zr had the highest specific surface area. BC700-Zr and BC700-Fe exhibited higher nitrogen removal efficiency. The biochars exhibited nitrogen and phosphate desorption, while we observed no obvious phosphate desorption in BC700-Zr or BC700-Fe. Adsorption kinetics analysis indicated that adsorption processes of nitrate, nitrite and enrofloxacin were consistent with pseudo-second-order model, while ammonium and phosphate adsorption processes fitted pseudo-first-order model better. The biochar showed nitrogen and phosphate nutrients release effects, indicating potential application in saline–alkaline soil improvement. Multi-linear regression analysis indicated that nitrogen release was closely related to biochar nitrogen content, pH and average pore width. Phosphate release was inversely related to pH and positively related to average pore width.