|Other Abstract||The intensive use of antibiotics in aquaculture have seriously polluted the water environment. This research aimed to develop cost-effective biochar techniques for use in reducing antibiotics in water by screening low-cost biochars and improve its performance. Here, a variety of biochars were produced via the oxygen-limited and aerobic carbonization methods developed, and their physical and chemical properties and antibiotic adsorption properties were determined and assessed to screen out the biochar. Then, the preferred biochar (BC) was used as a carrier and catalyst to systematically explore the performance and mechanism of OTC adsorption and degradation by nano-manganese dioxide (nano MnO2) - BC composite and BC-peroxymonosulfate (PMS) system. The main outputs are as follows:
1) The bamboo willow biochar prepared via aerobic carbonization had the largest specific surface area (262.2 m2/g) and carbon content (60.30%), the lowest H/C value, and the best antibiotic adsorption performance. It adsorbed 11.98 and 10.12 mg/g of OTC and SMX, respectively, from a solution with an initial concentration of 50 mg/L of the antibiotics. The reed biochar and cotton stalk biochar prepared by oxygen-limited method also showed good antibiotic adsorption capacity. Taken together, reeds and cotton stalks were suitable for preparation under oxygen-limited conditions, while bamboo willow was suitable for preparation under aerobic conditions. The π-π electron donor-acceptor (EDA) interaction was the primary mechanisms for the adsorption of neutral and acidic pH. Electrostatic attraction further promoted OTC adsorption on BC at pH 8–10, whereas pore filling could contribute to SMX adsorption.
2) As Mn-loading increased (MnO2/BC mass ratios of 1:40–10), C and N contents of MBC decreased, whereas ash and O content regularly rose. The maximum adsorption capacity of MBC for OTC, obtained from the Langmuir model, reached 292.53 (MBC40), 360.50 (MBC20), and 383.39 mg g−1 (MBC10), which were about 19, 24, and 25 times higher than that of BC (14.56 mg g−1), respectively. MBC20 achieved maximum OTC adsorption at pH=5, little affected by NaCl (2, 10 mM) or NOM (0–20 mg L−1) concentrations, but enhanced by NaHCO3 (2, 10 mM, complexed the Mn2+ in the solution). The OTC removal was accompanied by Mn2+ release. After 24 h reaction at pH 5.0, OTC degradation rate was 58.5% and Mn2+ release reached 2.97 mg L−1. OTC removal was the combined result of its adsorption onto MBC20 and its degradation by nMnO2. The π-π EDA interaction between BC and OTC promoted the adsorption of MBC20 to OTC, and nMnO2 acted as an oxidant during the removal process.
3) BC had excellent PMS catalytic activity. At the experimental OTC dose (300 mL, 30 mg/L), the optimal process conditions for the OTC removal by the BC-PMS system were: pH = 8.0-9.0, BC dosage was 0.33g/L, and PMS dosage was 10 µM. Under such conditions, the removal rate of OTC was about 76.0% within 2 h. The system was little influenced by NaCl (0-50 mM) and NOM (0-20 mg L−1), but accelerated by NaHCO3 due to an increase in pH. The process of BC-PMS degradation of OTC was jointly promoted by free radical and non-free radical process. Among them, SO4·− was the main free radical affecting degradation. The excellent ability of BC-PMS system to remove OTC from simulated solutions and aquaculture water was little affected by water turbidity, pH, electric conductivity, and DOM. In addition, the BC in the system can be reused, which can effectively repair the OTC in the wastewater for many times.
In conclusion, biochar produced from local bamboo willow via aerobic carbonization was a cost-effective material for use either as a carrier of nano-MnO2 or along with PMS for the adsorptive removal and catalytic degradation of OTC. BC has the potential for commercial use in alleviating antibiotic contamination from aquaculture.|