Sorption Characteristics And Mechanisms Of Phenanthrene, Lindane And Ofloxacin Onto Biofilms From Natural Waters

Polycyclic aromatic hydrocarbons and organochlorine pesticides are two typical persistent organic pollutants.Because they are difficult to degrade,they can accumulate and persist in the environment and behave as"persistent."Their residues in the environment can cause three-effects on organisms and negatively affect the ecological environment.For a long time,polycyclic aromatic hydrocarbons and organochlorine pesticides have been the classical environmental organic pollutants.Their behaviors such as migration and transformation in the environment have always been one of the research hotspots in the environmental field.As an emerging environmental pollutant,antibiotics have a generally short half-life in the environment.However,due to its high production volume,usage,and emissions,it be continued to import from the various sources of pollution into the environment,and exhibits"pseudo-persistent"characteristics in the environment.In recent years,the transport and transformation of antibiotics in the environment have received increasing attention.Sorption of pollutants in water environment at the water-solid interface is usually one of the key steps affecting the migration and transformation behavior of pollutants,which greatly influences the subsequent processes such as bioaccumulation,degradation,transformation,and fate of pollutants.Biofilm from natural water is a natural solid material widely existing in water environment.It can influence the water environment behavior of pollutants through sorption and other effects.Most previous studies focused on the sorption characteristics of biofilms or their extracellular polymers on trace pollutants.It was found that natural solid materials such as soils/sediments,and their different types of organic carbon components have different effects on the mechanism and contribution of different types of organic pollutants.What types of organic carbon components are contained in natural water biofilms,and the sorption mechanism of these components on classical and emerging organic pollutants is not yet clear.Therefore,this study collected water samples from different natural waters in different seasons and cultured different batches of biofilms in the laboratory.Sorption characteristics of phenanthrene,lindane,and ofloxacin by different biofilms were studied by batch sorption experiments to determine the corresponding sorption isothermal models and parameters.The organic composition of the biofilm was characterized by ¹³C Nuclear Magnetic Resonance?NMR?,combined with infrared spectroscopy and X-ray photoelectron spectroscopy?XPS?.Based on the sorption parameters and the structure and composition of the biofilm,the effects of different organic components in the biofilm on the sorption of organic contaminants by the biofilm,and the relationship between the different organic carbon components and the K_OC values were analyzed.And the sorption mechanisms were also discussed.The results showed that the dominant organism in biofilm was algae.The carbohydrates,protein and total organic carbon?TOC?content in biofilms have obvious seasonal characteristics and all exhibited maximum values in summer.Elemental analysis and XPS analysis showed that the organic carbon in the biofilm penetrated the entire biofilm instead of only in the biofilm surface layer.Solid-state ¹³C NMR analysis showed that there are three types of organic carbons in the biofilm:aliphatic carbon,aromatic carbon and polar carbon.The content of aliphatic carbon is the highest?>74.6%?,indicating that the biofilm is a kind of natural organic matter rich in aliphatic carbon.The sorption data of biofilms on phenanthrene,lindane,and ofloxacin can all be fitted by a linear model.The sorption coefficient?K_d value?of biofilm sorption of phenanthrene,lindane,and ofloxacin was related to:phenanthrene?58.96 g/L?>lindane?5.31 g/L?>ofloxacin?2.68 g/L?.This is consistent with the relative size relationship of the octanol/water partition coefficient(K_OW value)of the three organic contaminants,indicating that the physicochemical properties of phenanthrene,lindane,and ofloxacin themselves influence the biofilm sorption capacity.The K_OC values of phenanthrene,lindane,and ofloxacin were positively correlated with the alkyl carbon.Biofilms with a high content of alkyl carbon have a strong ability to sorb organic pollutants.Amorphous structure of the alkyl carbon"solid-phase dissolution"and the distribution of organic pollutants,the performance of linear sorption.It was shown that aliphaticity can be used to predict the ability of biofilms to sorb lindane and phenanthrene,but it cannot predict the ability of biofilms to sorb ofloxacin.Aromaticity can be used to predict the ability of biofilms to sorb phenanthrene and ofloxacin,but it cannot predict the ability of biofilms to attract lindane.In summary,biofilm sorption of phenanthrene,lindane,and ofloxacin is mainly through the amorphous carbon“solid phase dissolution”and the distribution of phenanthrene,lindane,and ofloxacin.The size of the alkyl carbon in the biofilm determines the ability of biofilmto sorb organic pollutants.The results of this study will help to understand in depth the characteristics and mechanisms of the sorption of natural organic water pollutants on different types of environmental organic pollutants.