Degradation of Typical PPCPs During Anaerobic Digestion and in Soil

Degradation is a key natural attenuation mechanism governing the fate of PPCPs during anaerobic digestion (AD) and subsequent soil exposure. Nevertheless, the combined impact of this sequential treatment (AD followed by land application) remains poorly understood. This study evaluated the degradation characteristics of nine PPCPs during mesophilic AD in three distinct soil types. The concentration changes in the nine PPCPs were monitored after 0, 5, 10, 15, 20, 25, and 30 days of anaerobic incubation at 38 °C, as well as after 0, 2, 5, 8, 10, 12, 15, 20, and 30 days of dark incubation at 25 °C with humidity at 75% in three soils. AD effectively removed sulfamethoxydiazine, ciprofloxacin, and oxytetracycline (>80%). The removal efficiencies for carbamazepine, progesterone, triclosan, naproxen, and megestrol acetate were relatively poor, with the removal rates ranging from 50% to 80%, while gemfibrozil exhibited minimal degradation (<50%). The degradation behavior of nine PPCPs fits well with first-order kinetic equations. Calculated half-lives (days) in the three soils were as follows: sulfamethoxydiazine (20.39 to 23.10), carbamazepine (36.48 to 77.02), megestrol acetate (11.18 to 20.39), progesterone (6.08 to 23.90), ciprofloxacin (11.75 to 63.01), oxytetracycline (13.08 to 30.14), naproxen (7.79 to 40.77), gemfibrozil (8.45 to 30.14), and triclosan (14.75 to 46.21). The corresponding R² values ranged from 0.8882 to 0.9320 for sulfamethoxydiazine, 0.8579 to 0.9248 for carbamazepine, 0.8745 to 0.9658 for megestrol acetate, 0.9026 to 0.9560 for progesterone, 0.8147 to 0.9571 for ciprofloxacin, 0.8136 to 0.9063 for oxytetracycline, 0.8961 to 0.9156 for naproxen, 0.8802 to 0.9497 for gemfibrozil, and 0.9099 to 0.9457 for triclosan. Soil physicochemical properties significantly influenced PPCP degradation rates. Gemfibrozil warrants immediate attention due to its poor degradation; the five PPCPs presenting moderate concern-namely carbamazepine, ciprofloxacin, oxytetracycline, naproxen, and triclosan-require further risk assessment, while sulfamethoxydiazine, megestrol acetate, and progesterone pose low persistence risk according to current evidence.