生物降解对黑碳及土壤上苯酚脱附行为的影响

农业土壤和黑碳(BC)两种不同的吸附剂吸附苯酚平衡后分离,每组一部分不做处理,另一部分通过加入无酚灭菌溶液脱附平衡后分离,制备得到在不同吸附位点上吸附有苯酚的两类不同类型的4种吸附苯酚的吸附剂,研究了在不同Pseudomonasputida ATCC 11172菌密度条件下吸附在这4种吸附剂上的苯酚的脱附行为.结果表明,土壤及BC对苯酚的吸附均呈现明显的非线性,可用Freundlich模型描述.吸附态的苯酚能否被微生物利用取决于微生物及吸附剂的性质,BC具有发达的微孔结构,微孔小于假单胞菌细胞尺寸,导致假单胞菌无法直接利用吸附在BC上的苯酚；土壤基本无微孔结构,微生物较易与吸附的苯酚发生表面接触,直接利用吸附态苯酚.BC和土壤上的吸附态苯酚的脱附行为能用三元位点模型很好地描述,模型计算结果表明BC上的苯酚脱附主要受慢速脱附和极慢速脱附控制,微生物降解速率受脱附控制,降解可加速BC上的慢速脱附和极慢速脱附；土壤上的苯酚脱附主要受快速脱附控制,微生物降解不受脱附速率限制,对土壤上的脱附行为基本无影响.

Impacts of biodegradation on desorption of phenol adsorbed on black carbon and soil

Desorption from natural absorbents is an underlying process affecting the transport, chemical activity, and biodegradation of organic compounds in the environment. It is commonly understood that biodegradation of sorbed organic compounds involves at least two rate processes of desorption and biodegradation. These two rate processes, desorption and biodegradation, are both controlled by the concentration of organic compounds in liquid phase, thus the liquid-phase concentration of substrate is both the result of, and the driving force for, the two rate processes. In most natural environments, however, this situation may be further complicated by the interactions of the two processes. Previous studies mainly focused on the effects of desorption on biodegradation and bioavailability of organic contaminants, little is known about how the biodegradation process affects the desorption process. In the present study, twelve desorption systems derived from four adsorbents of two different types, prepared by treatments after adsorption equilibrium of phenol on agricultural soil and black carbon (BC), were used to investigate the desorption behavior of the phenol on the four adsorbents under the different bacterial densities of Pseudomonas putida ATCC 11172. The majority of phenol were adsorbed within the micropores of BC which was characterized to possess more micropore structures compared to the soil. All the sorption isotherms of phenol by the adsorbents were nonlinear, which were well fitted by Freundlich adsorption model. The results demonstrated that the biodegradation of phenol was rate-limited, depending on desorption rate of phenol from BC, while desorption was controlled by the biodegradation rate for the phenol sorbed on soil. The desorption data were fitted to a three-compartment model which divided the desorption into rapidly, slowly and very slowly desorbing compartments, and the respective parameters were calculated. As expected, desorption rate constants for three-compartment model followed the progression of rate constant of rapid desorption (r_q) > rate constant of slow desorption (r_s) > rate constant of very slow desorption (r_vs). Accompanied with cell density increasing in BC desorption systems, the rapidly desorbing fractions and slowly desorbing fractions increased by approximately 2-10 times, the very slowly desorbing fractions decreased by 40%-60%, and the rate constant of desorption for each fractions approximately maintain stable for the phenol adsorbed by BC. In contrast, for the phenol sorbed by soil, the three desorbing fractions did not change notably while the respective rate constant of desorption increased. These results indicated that the three desorbing fractions of phenol were related to surface structure of the adsorbents. For phenol sorbed on BC, the overall desorption was dominated by slowly and very slowly desorbing compartments and biodegradation rates were limited by desorption rates. Biodegradation could accelerate desorption rates of slowly and very slowly desorbing compartment of phenol on BC. For phenol sored on soil, however, the overall desorption was dominated by rapidly desorbing compartments, biodegradation rates were not limited by desorption rates and in turn could not affect each of the three desorbing compartments. In addition, the bioavailability of phenol in this study was related to the properties of microorganisms and absorbents. Microorganisms could not access the phenol sorbed in the micropores on BC due to the size of cell which was physically excluded from the micropores.