Removal Of Ciprofloxacin And Trimethoprim In Soil Infiltration System And Its Effect On The Quality Of Reclaimed Water

The secondary effluent output of the urban sewage treatment plant is large and the quality of water and water is relatively stable.The secondary effluent of the urban sewage plant is recharged underground,which is an effective way to solve the problems of water shortage and excessive groundwater exploitation in China.In the process of percolation treatment of reclaimed water,micro-trace organic pollutants will have an important impact on the quality of the reclaimed water obtained,which is a research hotspot in this field.Soil percolation,as an advanced treatment and regeneration technology of reclaimed water widely used abroad,has a good effect in the removal of various pollutants.As an important antibiotic production and consumption country,China has a large number of antibiotics that are not used by humans and animals every year to enter the water environment and eventually enter urban sewage treatment plants.In the secondary effluent of the actual sewage treatment plant,although antibiotic substances are usually present in concentrations of μg/L or even ng/L,trace amounts of antibiotics enriched in the soil infiltration system will have an effect on the treatment effect and the resulting reclaimed water quality.influences.This paper aims to reveal the removal efficiency and degradation mechanism of ciprofloxacin(CIP)and trimethoprim(TMP)in soil infiltration systems,and to establish a soil infiltration system in the laboratory.The study found that the removal rate of CIP in soil infiltration system was about 97.4%,and the removal rate of TMP was about 92%.From the contribution of soil infiltration system at different heights to the removal of antibiotics,the surface soil layer 50 cm contributed a lot to the removal of CIP,accounting for 70.79% of the total soil column removal efficiency of CIP.For TMP,the 25-75 cm segment is the main contributor to TMP removal.57.39% of the TMP removed from the reactor was removed during this period,and the 75-100 cm layer removal contribution was 35.06%.Adsorption of pollutants by soil in soil infiltration system and microbial degradation in soil are very important for the removal of pollutants.The results of the equilibrium oscillation adsorption experiment indicated that the saturated adsorption capacity of CIP in soil was about 55 mg/g,and it took about 30 min to reach the saturation of adsorption.The adsorption amount of CIP in soil was the highest at p H 5.The saturated adsorption capacity of TMP in soil was about 60 mg/g,adsorption saturation occurs within 10 min,and the amount of TMP adsorbed by soil decreases with increasing p H.Organic matter has a catalytic effect on adsorption,and the adsorption of CIP and TMP by soil is an endothermic process.Adsorption kinetics simulation results show that the soil CIP and TMP adsorption results are consistent with the pseudo second-order reaction kinetics equation.Both the Freundlich model and the Langmuir model can better fit the adsorption isotherms of CIP and TMP in the soil,but fitting with the Langmuir model is better.At the same time,the removal effects and mechanisms of CIP and TMP under aerobic conditions,nitric acid reduction conditions,sulfuric acid reduction conditions and anaerobic conditions under four different redox conditions were studied in depth.The results showed that the removal effect of CIP under aerobic conditions was the most obvious.The final stable removal rate of the cartridge reached 70.75%;TMP under anaerobic conditions had the best degradation effect and the removal rate was close to 59%.Residual antibiotics in the effluent of the percolation system will generate certain carbon-containing and nitrogen-containing disinfection by-products during the reprocessing of the reclaimed water.In this dissertation,the chlorination disinfection experiments of CIP and TMP were conducted.The effects of different factors on the formation of new nitrogen-containing disinfection by-products chloronitromethane and dichloroacetonitrile were investigated.Studies have shown that during the chlorination reaction of CIP and TMP,the time for chlorination,the dosage of disinfectant,and the p H of the solution all have a certain influence to the production of nitrogen-containing disinfection byproducts(chloronitromethane and dichloroacetonitrile).