Remediation of Field Agricultural Soil Contaminated with Both Heavy Metals and Veterinary Antibiotics by a Degrading Strain-biochar Composite at Different Temperatures and Combinative Conditions

Coupled effects of biochar and antibiotic degrading bacterial strain on remediating contaminated soils with both heavy metals and antibiotics are poorly understood. A novel bio-based material combing an antibiotic degrading bacterial strain Herbaspirillum huttiense (HHS1) with biochar derived from spent mushroom substrate (BSMS) was developed, and an orthogonal test was conducted on soil contaminated with heavy metals and veterinary antibiotics. The stabilization of copper (Cu) and zinc (Zn) and the removal of oxytetracycline (OTC) and enrofloxacin (ENR) by the novel material at different temperatures were determined. Results indicated that the combination of BSMS and HHS1, along with temperature, was vital for pollutant treatments. The immobilized HHS1 (2 wt%)-BSMS (10 wt%) pellets achieved great stabilization efficiencies of Cu (69.2%) and Zn (59.72%), whereas higher removal of OTC (41.87%) and ENR (42.91%) was observed using HHS1 liquid and BSMS without entrapment at 35 ℃. The degradation of OTC and ENR by HHS1 accounted for 44.7% and 50.0% of their total removal, respectively. Oxytetracycline and ENR could be broken into small molecule products under low pH and high temperature through mechanisms including carbonylation, dihydroxylation, and piperazine ring-opening etc. When considering Cu and Zn stabilization, together with OTC and ENR removal in soils simultaneously, immobilized HHS1 (2 wt%)-BSMS (10 wt%) pellets are suitable for animal farms, even at low temperature (15 ℃), acting as an important bioresource for effectively stabilizing Cu and Zn and removing OTC and ENR in soil.