Study On The Microbial Response Mechanism Of Ibuprofen And Cadmium Wastewater Treated By Activated Sludge Process

Ibuprofen?IBU?is a class of non-steroidal anti-inflammatory drugs,because of its low toxicity,good curative effect and small side effects,it has become one of the most widely used analgesic antipyretic and anti-inflammatory drugs.Divalent Cadmium?Cd?II??,as one of the most valuable heavy metals,has been widely used in various industrial processes.However,IBU and Cd?II?entering the water can cause certain human diseases while poisoning aquatic organisms.Therefore,in this study,the activated sludge method was used to treat the IBU-and Cd?II?-containing wastewater for 60 days respectively to study the overall performance of the reactor,the evolution of the extracellular polymeric substances?EPS?and the microbial community.In addition,the abundance of Cd?II?resistance gene CzcA and its potential host bacterial changes were also investigated.The results are as follows:?1?IBU-containing wastewater was treated by activated sludge process,with the increase of IBU concentration?0-5 mg/L?,the removal efficiencies of COD and ammonia nitrogen?NH₄⁺-N?are all maintained over 95%and relatively stable.The removal efficiency of total nitrogen?TN?decreased slightly,but was always higher than 80%,while total phosphorus?TP?fluctuated around 75%.The removal efficiency of IBU showed a downward trend firstly,then stable at about 40%.The content of EPS?mainly proteins and polysaccharides?from sludge samples was determined,the results showed that the protein content?in 1 g MLSS?increased significantly from 3.49±0.22 mg on day 0 to 8.06±1.03 mg on 30th day and 11.49±0.40 mg on 60th day?p<0.05?,indicating bacteria was more prone to release proteins to protect cells from IBU damage.Determination of the chemical composition of EPS by three-dimensional fluorescence spectroscopy?3D-EEM?,showing the fulvic acid-like substances in the chemical composition of EPS increased from the 30th day to 60th day.?2?With the increase of IBU concentration,the diversity of microbial community first showed a significant decrease?days 0-30?and then gradually increased?days 30-60??p<0.05?.The dynamic changes of the microbial community were studied,and the results showed that at the genera level,Acinetobacter was the dominant genera under IBU stress.The research on functional bacteria showed that the significant proliferation of some denitrifying bacteria?such as Acidovorax?and polyphosphate?such as Pseudomonas?in activated sludge was an important reason for the high nitrogen and phosphorus removal efficiency in this study.Studies on the gene prediction of functional proteins and enzyme have found that the expression of the large subunit of nitric oxide reductase under IBU pressure increased significantly from 1393±186 on day 0 to 3537±3 on 30th day and 8388±147 on 60th day?p<0.05?,indicating that this functional enzyme can resist IBU stress and play a role in nitrogen removal.?3?Activated sludge was used to treat Cd?II?-containing wastewater,with the increase of Cd?II?concentration?0-20 mg/L?,the removal efficiency of COD was all greater than 85%.The removal of NH₄⁺-N and TN always display a decreasing trend,the average removal efficiency of NH₄⁺-N and TN is even as low as 24%and 40%respectively in the stable operation stage.The average removal efficiency of TP is 71.08%±0.37%,the higher TP removal may be related to the large proliferation of denitrifying polyphosphate?including Dechloromonas and Candidatus_Accumulibacter?in activated sludge.The removal efficiency of Cd?II?has always maintained above 80%during the whole operation,the EPS biosorption and the efflux pump function of microorganisms may play an important role in coping with Cd?II?stress.With the addition of Cd?II?,the protein content?in 1 g MLSS?in the EPS increased significantly from0.76±0.10 mg on day 0 to 3.39±0.75 mg on 30th day and 1.07±0.64 mg on 60th day,however,the polysaccharide content decreased significantly from 20.91±0.78 mg to 10.33±0.45 mg?days 0 to 60??p<0.05?,indicating that bacteria prefer to release protein to adsorb Cd?II?and protect bacteria from Cd?II?damage.The analyze of 3D-EEM showed that fulvic acid-like substances were the most abundant chemical components of EPS.?4?After the addition of Cd?II?,the diversity and richness index of microbial community in activated sludge showed a significant decreased trend?p<0.05?.Analysis of the dynamic evolution of microbial communities revealed that Flavobacterium was the dominant cadmium-resistant genus with the relative abundances of 43.84%?30th day?and 36.62%?60th day?.The results of functional microorganism showed that Cd?II?stress can inhibit the reproduction of most denitrifying bacteria?such as Thauera,Paracoccus,Hyphomicrobium,Comamonas,Rhodobacter,Pseudomonas?,ammonia oxidizing bacteria?such as Nitrosomonas?and nitrite oxidizing bacteria?such as Nitrospira?,which is also an important reason for the low removal efficiency of nitrogen compounds in this study.In the study of functional prediction,it was found that the expression of the predicted metal-dependent hydrolase and Cd²⁺/Zn²⁺output ATPase on 30th day and 60th day were significantly higher than on day 0?p<0.05?,indicating that these enzymes play an important role in Cd?II?resistance.In addition,qPCR was used to perform quantitative analysis of Cd?II?resistance gene CzcA,showing that CzcA gene abundance decreased as the Cd?II?concentration increased significantly during acclimation stage,however,the abundance of the CzcA gene increased slightly in the stable operation phase?p<0.05?.Analysis of the dynamic changes in the bacterial community in which the CzcA gene is located,showing that the majority of CzcA gene sequences were carried by Pseudomonas,making it the dominant host bacteria of CzcA gene.