Synergistic experimental study by a solar pilot evaporation system for the volume reduction and antibiotics photocatalytic degradation of liquid digestate

Abstract

The challenges posed by the large volume, low nutrient content, and high antibiotic concentrations in the liquid digestate from anaerobic digestion are becoming increasingly prominent. In this study, a solar pilot system was used for the evaporation and volume reduction of the liquid digestate and the photocatalytic degradation of antibiotics in the liquid digestate. First, given the difficulty in recovering the powdered catalyst, dolomite-supported g-C3N4 (DCN) was synthesized using a simple one-pot method, and its photocatalytic properties were investigated. The results indicated that the photocatalytic performance of DCN was excellent when the urea-to-dolomite doping ratio was 1:8, and the degradation efficiency of tetracyclines (TCs) in the real liquid digestate reached 90.65 % when the amount of DCN/1:8 was 0.625 g/mL. The TCs degradation efficiency increased as the initial pH of the liquid digestate decreased, reaching 95.33 % at an initial pH of 4, which could be attributed to the acidic conditions that are favorable for the generation of hydroxyl radicals and excited oxygen. Furthermore, the DCN was filled directly into a solar pilot system, which was employed for the evaporation reduction treatment of the liquid digestate as well as the photocatalytic degradation of antibiotics under optimal process conditions. The pilot experiment showed that the average TCs degradation efficiency rose from 57.54 % to 95.27 % with the addition of DCN/1:8 to the solar evaporation system. After a 4-day replicated experiment, the average TCs degradation efficiency reached 90.64 %. Importantly, DCN/1:8 had less of an effect on the evaporation efficiency of the liquid digestate and the recovery of key nutrients, such as NH4+-N. This study aims to demonstrate the engineering, theoretical, and technological feasibility of sunlight photocatalytic degradation of antibiotics in complex water quality systems and to provide a reference for the reduction and harmless treatment of liquid digestate.