جذب سطحی آنتی بیوتیک های کینولون توسط سلولهای میکروبی در لجن
Abstract
1- Introduction
2- Materials and methods
3- Results and discussion
4- Conclusions
References
Abstract
Traditional wastewater treatment plants cannot completely remove trace pharmaceutical and personal care products. In particular, quinolone antibiotics are mainly adsorbed on microbial cell surfaces in excess sludge and are released into the water environment during agricultural supplementation, mainly due to the exfoliation of extracellular polymeric substances (EPS) caused by changes in environmental conditions. Here, the occurrence of seven typical quinolone antibiotics from three generations in excess sludge was investigated at trace concentrations using ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). EPS facilitated adsorption independent of pH and quinolone antibiotic type, and the solid-liquid distribution coefficient decreased markedly as pH increased (pH 5–9, range of municipal wastewater). Metal ions bound in EPS were predominantly responsible for the adsorption of antibiotics in sludge, rather than the macroscopic size of the sludge floc. pH affected patterns of quinolone antibiotics, the zeta potential of sludge floc, and the contents of metal ions contained in sludge. The adsorption capacity of antibiotics first increased and then decreased with increasing pH in the range of pH 3–11, reaching a maximum (20,506, 14,458, 10,689, 22,854, 20,302, 8494, and 29,547 L/kg for CIP, ENR, LOM, MOX, NOR, OFL, and SAR, respectively) near pH 5, at which the cationic bridging of Ca2+ and Mg2+ bound in EPS played a major role owing to their larger ion radius and higher contents in excess sludge. Due to high surface heterogeneity of sludge, the Freundlich model was more suitable than the Langmuir model for describing the adsorption behavior of quinolone antibiotics. These results provide further insight into the release of quinolone antibiotics adsorbed in excess sludge, with potential implications for the agricultural use of sludge.
Introduction
Trace pharmaceutical and personal care products (PPCPs) have been detected in environmental media such as surface water, groundwater, and soil. Although the concentration of PPCPs related to human activities is usually on the order of nanograms to micrograms per liter in the water environment [1–5], many PPCPs are discharged continuously into the environment, causing potential risks for human health and the environment due to their ongoing utilization [6–9]. Wastewater treatment plants (WWTPs) are one of the main point sources of PPCP discharge into the environment [10], as it is difficult to biochemically degrade these substances during the conventional wastewater treatment process [11]. As a result, except for a small amount of PPCPs that are released into the atmosphere by escape, some portion of PPCPs remains in the effluent of the wastewater treatment plant, with the remainder present in excess sludge due to adsorption or dissolution [12]. The Water Pollution Prevention Action Plan promulgated in April 2015 in China stipulates that treated sludge cannot contain potential environmental pollutants [13]. When excess sludge containing PPCPs is used for land use and agricultural production activities such as fertilization, PPCPs in the sludge may be released into the environment as the external environment changes [10,14–19], thereby contaminating surface water and groundwater [4,12,18–20]. In recent years, quinolone antibiotics have been one of the most widely used antibiotics in veterinary and medical applications [21]. In China, they are widely used in human clinical settings and livestock breeding for disease prevention, with livestock and poultry farming accounting for about 50% of their use [22]. Moreover, the consumption of quinolone antibiotics has increased significantly; for example, the annual consumption of quinolone antibiotics in humans and animals in 1998 was 1,350 and 470 tons respectively [23], while the annual consumption of ciprofloxacin, norfloxacin, ofloxacin, lomefloxacin, and enrofloxacin in China in 2013 for both humans and animals reached 5340, 5440, 5110, 1250, and 5180 tons, respectively [22].