Domoic acid

Microalgae-based biotreatment offers a sustainable and efficient solution for managing pig manure anaerobic digestion effluents (PMADE), a byproduct of intensive agricultural practices. Dissolved organic matter (DOM) in PMADE significantly influences microalgal physiological responses; however, the underlying mechanisms remain poorly understood. Here, we reveal a hormetic effect of DOM in PMADE on Chlorella sp. Moderate DOM concentrations (1000-1500 mg/L of COD) alleviated ammonium toxicity and promoted microalgal growth, whereas higher concentrations (>2000 mg/L of COD) exerted severe inhibitory effects. Through cascade extraction and targeted screening, we identified distinct impacts of five DOM fractions on Chlorella sp. Notably, low-molecular-weight acids and nitrogenous compounds, primarily dipeptides in the fractions, exhibited a promoting effect on growth by serving as carbon sources to enhance energy metabolism and protein synthesis. Among the fractions, antioxidant-active compounds further supported the growth by scavenging reactive oxygen species (ROS) and maintaining redox homeostasis. In contrast, fractions rich in alkanes and alkaloids, induced excessive ROS production under high concentrations, leading to impaired photosynthesis and severe DNA damage. Additionally, the substances such as humic acid and fulvic acid, as key components of PMADE, exhibited hormetic effects: at specific concentrations (humic acid<200 mg TOC/L; fulvic acid<100 mg TOC/L), they enhanced ROS scavenging, growth, photosynthesis and pigment accumulation, whereas exceeding these thresholds shifted their role from promotion to inhibition. Collectively, this study elucidates the dose-response relationship between DOM concentration and composition in relation to microalgal growth, identifies key DOM components influencing growth, and proposes targets for the selective removal of inhibitory DOM in PMADE.

Previous studies have shown that O₃/Peroxymonosulfate (PMS) outperforms O₃ alone in treating refractory pharmaceuticals and personal care products. However, research on the removal of antibiotics using O₃/PMS remains limited, and the effectiveness of this process in removing antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) remains unclear. In this study, the treatment performance of O₃ and O₃/PMS for antibiotic-containing wastewater were comprehensively compared, particularly on the effectiveness of O₃/PMS in inactivating ARB and reducing ARGs abundance compared with O₃. Within 15 min of treatment, O₃/PMS removed up to 52.3 % more targeted antibiotics, 4.8 % more dissolved organic carbon, 2.7 % more UV₂₅₄, and 18.8 % more dissolved organic matter (DOM) than O₃. For ciprofloxacin-resistant and chloramphenicol-resistant bacteria, both O₃ and O₃/PMS showed a continuous decrease in concentration with increasing treatment time. For amoxicillin-resistant, tetracycline-resistant, and sulfamethoxazole-resistant bacteria, O₃ showed an initial increase followed by a subsequent decrease, while O₃/PMS showed a similar trend for tetracycline- and sulfamethoxazole- resistant bacteria, but a continuous decrease for amoxicillin-resistant bacteria. For ARGs, before 8 min, O₃ treatment showed a higher relative abundance of targeted ARGs (0.01-0.31 ARGs/16S rRNA), mainly due to tetQ. After 8 min, O₃/PMS treatment exhibited a higher relative abundance of ARGs/16S rRNA (0.04-0.05), primarily due to floR. At the phylum level, PMS addition increased Bacteroidota abundance while reducing Proteobacteria, Chloroflexota, and Myxococcota_A_473307. At the class level, PMS specifically promoted Alphaproteobacteria and Bacteroidia while inhibiting Gammaproteobacteria and UBA9160. Finally, the acute toxicity of O₃/PMS-treated wastewater was 14.6 % lower than that of O₃-treated wastewater at 2 min. However, after 6 min, the toxicity of O₃/PMS-treated wastewater became significantly higher, with the largest difference (23.6 %) observed at 8 min. The results indicated that O₃/PMS had an advantage over O₃ in removing antibiotics, DOM, and controlling ARB. However, prolonged treatment increased ARGs diversity and concentration compared to O₃ and significantly enhanced the acute toxicity of antibiotic-containing wastewater.