Simultaneous Adsorption Performance Of Sulfamethoxazole,Cr(Ⅵ) And Dimethyl Phthalate Onto Different Substrates

Contamination by pharmaceutical and personal care products（PPCPs）,trace metals and endocrine disrupting chemicals（EDCs）,such as SMX,Cr（Ⅵ） and DMP,becomes more serious caused by a large number use of these compounds.The environmental effect from various pollutants is no longer single and forms complex contamination.Adsorption technology has been widely used in control pollution of PPCPs,heavy metals and EDCs.In this study,new adsorbents were successfully synthesized based on MgAl-layered double hydroxides（LDH） and biochar（BC） derived from Pennisetum sinese Roxb.Some natural substrates,such as vermiculite,zeolite,river sand,feldspar,limestone,volcano rock,diatomite,blast furnace slag,paddy soil and peat,were also used to adsorb SMX and Cr（Ⅵ） by batch experiments.Column shaped biochar,zeolite,vermiculite,peat and river sand were chose to adsorb SMX and DMP by batch experiments and simulated vertical flow constructed wetland,according to the performance for adsorbing SMX and Cr（Ⅵ）.The study purposes are to find promising adsorbents for the simultaneous removal of trace SMX and Cr（Ⅵ）,as well as simultaneous removal of SMX and DMP.The main conclusions are as follows:（1）To optimize adsorption performance of Mg Al-layered double hydroxides（LDH） and biochar（BC） derived from Pennisetum sinese Roxb,the composites were synthesized based on the above two adsorbents by mass ratios as 2:1,3:1 and 4:1 and characterized the composites.The results showed that the composites were successfully prepared with properties of both LDH and BC.The BC reserved pore structure,large surface area and enough oxygen-containing functional groups.The LDH remained high crystallinity layer structure,and the composites obtained adsorption ability of both BC and LDH.（2）The adsorption performance of the composites for adsorbing trace SMX and Cr（Ⅵ） was investigated by batch experiments.The results showed that adsorption of SMX and Cr（Ⅵ） was well-described by the pseudo-second-order model and the Freundlich model rather than the pseudo-first-order model and the Langmuir model.The fitted adsorption model indicated that SMX and Cr（Ⅵ）adsorbed on the composites by the comprehensive effect of surface chemical adsorption and distribution.In the neutral solution,Efficient adsorption of SMX onto LB3 is synergistic effect of π-π EDA,hydrophobic interaction,hydrogen bonding and electrostatic interaction.Electrostatic effect was the smallest part in synergistic effect.However,LB3 adsorbed Cr（Ⅵ） by anion exchange,electrostatic interaction and hydrogen bonding,of which electrostatic interaction was the largest part.The main factor affecting electrostatic adsorption was solution pH,which promoted electrostatic interaction between adsorbates and adsorbents at low pH,and limited the electrostatic interaction at high pH.（3）According to the performance of BC and LDH for adsorbing SMX and Cr（Ⅵ）,the performance of ten different substrates in constructed wetlands for adsorbing SMX and Cr（Ⅵ） was evaluated.The substrates included vermiculite,the same as LDH,which is also the clay mineral,and peat which has enough surface functional groups.The results suggested that the adsorption of SMX and Cr（Ⅵ） onto the ten substrates was well-described by the pseudo-second-order model and Freundlich model.The fitted model indicated that there was occurred chemical action between adsorbates and adsorbents in multilayer adsorption.SMX and Cr（Ⅵ） adsorption capacity decreased with the increase of pH which caused by electrostatic interaction.The electrostatic attraction increased in the binary solution,especially between Cr（Ⅵ） and the substrates.The optimized substrate was peat,which had higher adsorption capacity of SMX,as well as higher adsorption capacity of Cr（Ⅵ）which was just below the volcano rock.Besides,vermiculite,zeolite and river sand could be the optimized substrates for adsorbing SMX and Cr（Ⅵ） due to their faster adsorption rate and stable adsorption performance.（4）SMX and DMP were further selected to be adsorbed onto five optimized substrates including biochar,vermiculite,zeolite,peat and river sand by batch experiments,excluded Cr（Ⅵ） due to its lower adsorption capacity onto all the substrates.The performance of five substrates including biochar,zeolite,vermiculite,peat and river sand for adsorbing SMX and DMP were investigated by batch experiments.The results revealed that the adsorption of SMX and DMP onto the five substrates was well-described by the pseudo-second-order model and Freundlich model.The adsorption capacity of SMX decreased,while the adsorption capacity of DMP increased obviously in the binary solution than that in the single solution.Increasing the initial p H of the solution is beneficial to DMP adsorption onto each substrate,which is not conducive to SMX adsorption.When the solution p H was 7,the river sand could simultaneously adsorb 6.04 mg/g SMX and 9.97 mg/g DMP,while biochar can simultaneously adsorb 6.06 mg/g SMX and 9.99 mg/g DMP,both of which have advantages over other substrates in simultaneous adsorption of SMX and DMP.（5）Simulated columns were constructed to remove SMX and DMP,which filled by the above five substrates according to their high performance on adsorbing SMX and DMP.The results showed that the presence of other pollutants in sewage could promote the simultaneous removal of SMX and DMP with effective removal 92.94%SMX and 94.99% DMP.SMX and DMP could promote the removal of COD_Cr and TN,but inhibited the removal of TP and NH₄⁺-N,especially NH₄⁺-N.