Degradation Characteristics Of Sulfamethoxazole(SMX) And Influencing Factors During Composting Of Sewage Sludge

In recent years,ecological effects caused by pharmaceuticals detected in the environment have raised much concern,and wastewater treatment plants are regarded as one of the important sources.Various types of pharmaceuticals have been reported to be adsorbed by activated sludge during biological processes.Pharmaceuticals contained in sewage sludge would cause concerns of their contamination of food,soil and groundwater in the environment if sewage sludge would be applied to agricultural land as fertilizers.Therefore,treatment of pharmaceuticals in sewage sludge is of great importance.Composting is a commonly used technique for the stabilization of sewage sludge.Composting can transform biodegradable waste into nutrient-rich compost which can be used as a fertilizer or soil conditioner.Some organic chemicals such as pharmaceuticals should be eliminated to reduce a risk.To ensure the safety of the composing products applied to farmlands,affecting factors for the removal of pharmaceuticals during composting should be analyzed.In this study,the mixture of sewage sludge and sawdust was as composting materials,and forced aerated composting was carried out using a lab-scale reactor to investigate the dynamics of sulfamethoxazole(SMX),a kind of antibioticfrequently detected in sewage sludge,during composting of sewage sludge.A series of experiments were conducted to clarify the degradation of SMX during composting.1)The SMX in sewage sludge was extracted by ultrasonic treatment.The recovery of SMX in the sludge under different conditions was compared and the optimal operating conditions were determined.It was found that when the ultrasonic power was 562.5W and the ultrasonic treatment time was 10 minutes,the recovery rate of SMX in the sludge was the highest,which reached at 92.19%.In the step of solid-phase extraction purification,the solution eluted from the solid-phase extraction column was directly made up to ultrapure water,and the recovery of the target was higher than that of the elution solution that was first dried under nitrogen flow and then reconstituted.2)The temperature of the composting process was controlled at30°C to study the removal of SMX during the composting process.It was observed that SMX concentration of SMX in the compost material decreased rapidly with the active degradation of organic matter at a temperature of 30°C and air supply of 1.7 ml/min/g TS.At the end of the second day of composting,the removal efficiency of SMX reached more than 80%.It can be concluded that the aerobic composting process can effectively remove SMX from sewage sludge.3)The sludge is subjected to high temperature sterilization treatment to examine the effect of microorganisms on the degradation of SMX in the sludge at the initial stage of composting.The dewatered sludge from the sewage treatment plant was sterilized at 121°C and then composted.As a result,it was found that the degradation rate of SMX in the sludge is significantly reduced after the high temperature sterilization treatment.At the temperature of 30°C,the degradation rate constant of SMX at the initial stage of composting was 0.7423 d~-11 in the experiment without high temperature sterilization treatment,which was calculated by first-order kinetics equation.While it was 0.1579 d~-11 after high temperature sterilization.Under the condition of the temperature of 45°C,the degradation rate constant was 0.9364 d~-11 in the experiment without high temperature sterilization.However,it was 0.1931 d~-11 in the experiment with high temperature sterilization.This shows that the microorganisms in the sewage sludge play an important role in the degradation of SMX during composting.4)Thecompostingexperimentsunderdifferenttemperature conditions(30°C,45°C,60°C)were conducted,and the effect of temperature on the degradation of SMX during composting was studied.It was found that degradation rate of SMX increased with the the increase of temperature.At 60°C,the degradation rate of SMX in sewage sludge was the highest,followed by 45°C and 30°C.The results indicate that the temperature has an important effect on the degradation rate of SMX during the composting.