Preliminary Study on the Treatment Efficiency of Pasteurized Lime Thermal Alkaline Hydrolysis for Excess Activated Sludge and Reduction of Tetracycline Resistance Genes

Thermal alkaline hydrolysis is a common pretreatment method for the utilization of excess activated sludge(EAS).Owing to strict environment laws and need for better energy utilization,new methods were developed in this study to improve the efficiency of pretreatment method.Direct thermal hydrolysis(TH),pasteurized thermal hydrolysis(PTH),and alkaline pasteurized thermal hydrolysis(PTH+CaO and PTH+NaOH)methods were used to treat EAS.Each method was compared and analyzed in terms of dissolution in ammonium nitrogen(NH_(4)^(+)-N)and soluble COD(SCOD)in EAS.Furthermore,the removal of tetracycline resistance genes(TRGs)and class 1 transposon gene intI1 from EAS was investigated.The NH_(4)^(+)-N and SCOD concentrations in EAS treated by PTH were 1.24 and 2.58 times higher than those of TH.However,the removal efficiency of total TRGs and intI1 between the groups was comparable.The SCOD concentration of the PTH+NaOH group was 4.37 times higher than that of the PTH group,and the removal efficiency of total TRGs was increased by 9.52%compared with that by PTH.The NH_(4)^(+)-N and SCOD concentrations of the PTH+CaO group could reach 85.04%and 92.14%of the PTH+NaOH group,but the removal efficiency of total TRGs by PTH+CaO was 19.78%lower than that by PTH+NaOH.Thus,to reduce the financial cost in actual operation,lime(CaO)can be used instead of a strong alkali(NaOH),and pasteurized steam at 70℃ instead of conventional high-temperature heating to treat EAS.This study provides a reference for the development of alkaline hydrolysis under moderate temperatures along with the removal of TRGs in EAS.

Optimized determination of airborne tetracycline resistance genes in laboratory atmosphere

Antibiotic resistance genes(ARGs)have been detected in various atmospheric environments.Airborne ARGs transmission presents the public health threat.However,it is very difficult to quantify airborne ARGs because of the limited availability of collectable airborne particulate matter and the low biological content of samples.In this study,an optimized protocol for collecting and detecting airborne ARGs was presented.Experimental results showed that recovery efficiency tended to increase initially and then declined over time,and a range of 550-780 copies/mmz of capture loading was recommended to ensure that the recovery efficiency is greater than 75%.As the cell walls were mechanically disrupted and nucleic acids were released,the buffer wash protects ARGs dissolution.Three ratios of buffer volume to membrane area in buffer wash were compared.The highest concentrations of airborne ARGs were detected with 1.4μL/mm^2 buffer wash.Furthermore,the majority of the cells were disrupted by an ultrasonication pretreatment(5 min),allowing the efficiency ARGs detection of airborne samples.While,extending the ultrasonication can disrupt cell structures and gene sequence was broken down into fragments.Therefore,this study could provide a theoretical basis for the efficient filter collection of airborne ARGs in different environments.An optimized sampling method was proposed that the buffer wash was 1.4 nL/mm and the ultrasonication duration was 5 min.The indoor airborne ARGs were examined in accordance with the improved protocol in two laboratories.The result demonstrated that airborne ARGs in an indoor laboratory atmosphere could pose the considerable health risk to inhabitants and we should pay attention to some complicated indoor air environment.