Das Keshav C, Xia Kang
Department of Biological and Agricultural Engineering, Driftmier Engineering Center, University of Georgia, Athens, GA 30602, USA.
Chemosphere. 2008 Jan;70(5):761-8. doi: 10.1016/j.chemosphere.2007.07.039. Epub 2007 Sep 7.
4-Nonylphenol, a degradation intermediate of commercial surfactant and known endocrine disruptor, has been frequently detected at levels up to several thousand microgl(-1) in surface waters and up to several hundred mgkg(-1) (dry weight) in soil and sediment samples. Large quantities of 4-NP can be quickly sorbed by the organic rich solid phase during wastewater treatment and are concentrated in biosolids, a possible major source for 4-NP in the environment. Microbial transformation in culture studies followed different mechanisms for different 4-NP isomers, which have different estrogenic activity. Composting is a process of solid matrix transformation where biological activity is enhanced by process control. This approach has been used successfully in remediation of contaminated soils and sludges. In this study, the transformation kinetics of 4-NP and its isomers were characterized during biosolids composting. Five distinctive 4-NP isomer groups with structures relative to alpha- and beta-carbons of the alkyl chain were identified in biosolids. Composting biosolids mixed with wood shaving at a dry weight percentage ratio of 43:57 (C:N ratio of 65:1) removed 80% of the total 4-NP within two weeks. At this biosolids/wood shaving ratio (B:WS), the transformation of total 4-NP and its isomers followed second-order kinetic. Higher B:WS ratios yielded significantly slower 4-NP transformation which followed first-order kinetic. Isomers with alpha-methyl-alpha-propyl structure transformed significantly slower than those with less branched tertiary alpha-carbon and those with secondary alpha-carbon, suggesting isomer-specific degradation of 4-NP during biosolids composting.
4-壬基酚是一种商业表面活性剂的降解中间体，也是已知的内分泌干扰物，在地表水、土壤和沉积物样本中常被检测到，其含量在地表水中高达数千微克/升，在土壤和沉积物（干重）中高达数百毫克/千克。在废水处理过程中，大量的4-壬基酚会迅速被富含有机物的固相吸附，并浓缩在生物固体中，这可能是环境中4-壬基酚的一个主要来源。培养研究中的微生物转化对不同的4-壬基酚异构体遵循不同的机制，这些异构体具有不同的雌激素活性。堆肥是一个固体基质转化的过程，通过过程控制可以增强生物活性。这种方法已成功用于污染土壤和污泥的修复。在本研究中，对生物固体堆肥过程中4-壬基酚及其异构体的转化动力学进行了表征。在生物固体中鉴定出了五个独特的4-壬基酚异构体组，其结构与烷基链的α-和β-碳相关。以43:57（碳氮比为65:1）的干重百分比比例将生物固体与木屑混合进行堆肥，在两周内去除了80%的总4-壬基酚。在这种生物固体/木屑比例（B:WS）下，总4-壬基酚及其异构体的转化遵循二级动力学。较高的B:WS比例导致4-壬基酚转化明显变慢，遵循一级动力学。具有α-甲基-α-丙基结构的异构体转化速度明显慢于那些具有较少支链叔α-碳和仲α-碳的异构体，这表明在生物固体堆肥过程中4-壬基酚存在异构体特异性降解。
