| Phthalate esters (PEs) are one of the most frequently detected persistent organic pollutions in the environment. As a primary plasticizers, They are already extensively used in industry and personal care productions. Due to the non-covalently bonded to the substrate material, PEs are easily released and then accumulated in the environment, interfering the biological processes inhumans and wildlife as endocrine disrupting chemicals. The removal and degradation of PEs have recently received an increasing negative attention. Constructed wetland system (CWs) is one kind of special ecosystem with the ecotone of water aquatic ecosystem and the terrestrial ecosystem, and it gathers PEs from different pathways, including atmospheric deposition, rainfall, wastewater and surface runoff. The biodegradation of PEs by PEs-degrading bacteria in CWs was analyzed, and the mechanism of the increased PEs removal efficiency was clarified during the formation of PEs-degrading bacteria biofilm on CWs substrate material, accompanied with PEs adsorption on substrate material.This study has investigated the adsorption mechanism of PEs to vermiculite and the effects of environmental factors on the adsorption process, especially humic acid (HA), using DEHP as a representative PEs. DEHP molecules were adsorbed on the surface of vermiculite in a monolayer and the acting force was mainly hydrophobic interactions. The adsorption isotherms were described quite well by Langmuir model (r>0.99), and the adsorption process was exothermic and spontaneous. The presence of HA in The system consistently inhibited the adsorption of DEHP to vermiculite by the competition for adsorption sites and the co-transport function. However, an excess of both HA and acidity weakened the inhibition of HA.PEs-degrading bacteria were isolated from CWs soil and the ability to degrade PEs and phthalic acid (PA) were evaluated. The biodegradation characteristics and relative degradation gene were also analyzed.15PEs-degrading bacteria were isolated from CWs soil, and they mainly belonged to Gammaproteobacteria and Actinobacteridae in Bacteria, involved in eight bacterial genus, in which, the biodegradation of PEs by Klebsiella sp. has not been reported. Arthrobacter sp. C21is capable of utilizing PEs with different alkyl-chains and PA. Kinetic analysis indicated that the strain C21cell growth on DBP fitted well with haldane-Andrew model (r>0.98) with μmax, Ks and Ki of0.12h-1,4.2mg/L and204.6mg/L, respectively. When DBP initial concentration was lower than100mg/L, DBP biodegradation reaction fitted with the first-order kinetics.Arthrobacter sp. C21could form biofilm on the surface of vermiculite in shorter time, and vermiculite is often used as CWs substrate materials. The formation of biofilm could strengthen DEHP elimination. There were three ways could be responsible for DEHP elimination during the formation of biofilm, and these three parts were adsorption of vermiculite, the biodegradation and the adsorption effect of biofilm, respectively. At the beginning of the formation of biofilm (0-5h), the bacteria adhesion was observed, Arthrobacter sp. C21biodegradation and vermiculite adsorption were the main mechanism for PEs remove. With the development of biofilm, bacteria C21gathered and replicated on surface of biofilm (5-36h), PEs remove mainly relied on biodegradation. Do research into the cause for increased DEHP degradation efficiency in biofilm system than suspension, found that the increase of biomass is one of the main factors. In addition, through the calculation specific substrate degradation rate, the results indicated that the degradation activity was enhanced obviously in biofilm. At the mature stages of biofilm (36-54h), biofilm adsorption was the main reason for PEs remove in the liquid pHase, and a small amount of PEs was used to maintain living organisms. Plenty of EPS were linked together and constituted the basic skeleton of biofilm, The hydropHobic components protein of biofilm was helpful for DEHP adsorption on biofilm. The analysis showed that EPS production and DEHP removalhad a significant positive correlation in biofilm system (rp＞0.86). In addition, the addition of carbon source into the system or adjusting pH also had influence on the biofilm activity. |
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