Tomei Maria Concetta, Annesini Maria Cristina
Water Research Institute, C.N.R., Via Reno 1, 00198 Rome, Italy.
Environ Sci Pollut Res Int. 2008 May;15(3):188-95. doi: 10.1065/espr2007.12.470.
GOAL, SCOPE AND BACKGROUND: In this study, attention was focused on substituted phenols because of their widespread presence in industrial effluents originating from many different sources: they are major constituents of wastewater from coal conversion processes, coke ovens, petroleum refineries and petrochemical industries, resin and fibreglass manufacturing and herbicide production. Moreover, for their characteristics of toxicity to humans and aquatic life (1 mgl(-1) is enough to detect the effects), they are included in the USEPA list of priority pollutants. Toxicity is higher in substituted phenols and is dependent on the nature and numbers of substituent groups. Objective of the present paper is to give a contribution to the modelling of phenolic mixture biodegradation by kinetic studies in which the different compounds are followed separately: this can be easily attained with an experimental apparatus such as the Sequencing Batch Reactor (SBR). Two substituted phenols, 4-nitrophenol (4NP) and 3,4-dimethylphenol (3,4DMP), were utilized as substrates and their degradation kinetics were investigated to evaluate the process parameters both in single compound and in mixture tests.
Single compound and mixture kinetic tests have been carried out during the reaction phase of the working cycle of the SBR reactor. The single substrates and their mixture were utilized as sole carbon and energy sources. Moreover, in order to verify data reproducibility, all kinetic tests have been carried out in at least two replicates under the same operating conditions.
Kinetic data showed the presence of substrate inhibition, to model this experimental evidence the Haldane equation, that is usually employed for substrate inhibited kinetics, was rearranged in a different form with parameters which have a precise meaning in relation to the process kinetics and, at the same time, make the integration procedure easier. The derivation of the equation is shown in an Appendix at the end of the paper. Kinetic parameters obtained are suitable for application. It was observed that the 4-nitrophenol removal rate in single compound tests is significantly higher than the 3,4-dimethylphenol removal rate in the whole range of investigated concentrations (up to 80 mg COD l(-1)). A faster 4-nitrophenol biodegradation was also observed in mixture tests. Moreover, it is worth noting that the two compounds were simultaneously degraded and no diauxic growth was observed. The comparison between single compound and mixture degradation kinetics showed that the 4-nitrophenol degradation rate was comparable in the two cases while a significantly beneficial effect (by increase by about 80% of the maximum removal rate) was detected for 3,4-dimethylphenol degradation in the mixture.
Results of this study showed that the biodegradation kinetics of substituted phenols in mixture can be significantly different from that observed in single compound tests: in fact, the presence of a faster degradable compound (the 4NP) seems to exert a positive effect on the removal of a slower degradable compound (the 3,4DMP). The higher removal rate detected for 4NP, both in single compound and mixture tests, confirmed the key role of the biomass acclimatization in determining the biodegradation kinetics of xenobiotic compounds. The experimental approach and the original method applied for data analysis are of general validity and can be extended to the investigation of different classes of compounds.
A relevant aspect related to the process applicability is the demonstrated possibility of easily adapting an enriched culture grown on a specific xenobiotic (in our case the 4NP) for the removal of similar single compounds or in mixtures. When biological process are considered for xenobiotic removal, this suggests a possible strategy of developing enriched cultures on target compounds that can be efficiently utilized on more complex matrices with reduced start up and acclimatization periods.
目标、范围及背景：在本研究中，由于取代酚广泛存在于源自多种不同来源的工业废水中，因此受到关注：它们是煤炭转化过程、炼焦炉、石油精炼厂和石化行业、树脂和玻璃纤维制造以及除草剂生产废水的主要成分。此外，由于它们对人类和水生生物具有毒性特征（1mg/L就足以检测到其影响），它们被列入美国环境保护局的优先污染物名单。取代酚的毒性更高，且取决于取代基的性质和数量。本文的目的是通过动力学研究为酚类混合物生物降解建模做出贡献，在该研究中对不同化合物进行分别跟踪：使用诸如序批式反应器（SBR）这样的实验装置可以轻松实现这一点。选用两种取代酚，4-硝基苯酚（4NP）和3,4-二甲基苯酚（3,4DMP）作为底物，并研究它们的降解动力学，以评估单一化合物和混合测试中的过程参数。
在SBR反应器工作周期的反应阶段进行了单一化合物和混合动力学测试。单一底物及其混合物用作唯一的碳源和能源。此外，为了验证数据的可重复性，所有动力学测试均在相同操作条件下至少重复进行两次。
动力学数据显示存在底物抑制现象，为对该实验证据进行建模，通常用于底物抑制动力学的哈代方程以一种不同形式重新排列，其参数在过程动力学方面具有精确含义，同时使积分过程更简便。方程的推导在本文末尾的附录中给出。获得的动力学参数适用于实际应用。观察到在单一化合物测试中4-硝基苯酚的去除率在整个研究浓度范围（高达80mg COD/L）内显著高于3,4-二甲基苯酚的去除率。在混合测试中也观察到4-硝基苯酚的生物降解更快。此外，值得注意的是两种化合物同时降解，未观察到二次生长现象。单一化合物和混合降解动力学的比较表明，4-硝基苯酚的降解速率在两种情况下相当，而对于混合中的3,4-二甲基苯酚降解检测到显著的有益效果（最大去除率提高约80%）。
本研究结果表明，取代酚混合物的生物降解动力学可能与单一化合物测试中观察到的显著不同：实际上，存在一种降解更快的化合物（4NP）似乎对降解较慢的化合物（3,4DMP）的去除产生了积极影响。在单一化合物和混合测试中4NP检测到的较高去除率证实了生物量驯化在确定异源化合物生物降解动力学方面的关键作用。所采用的实验方法和数据分析的原始方法具有普遍有效性，可扩展到对不同类别化合物的研究。
与该过程适用性相关的一个重要方面是，已证明可以轻松地将在特定异源化合物（在我们的案例中为4NP）上生长的富集培养物用于去除类似的单一化合物或混合物。当考虑采用生物过程去除异源物质时，这表明了一种可能的策略，即针对目标化合物培养富集培养物，该培养物可在更复杂的基质上高效利用，同时缩短启动和驯化周期。
