Degradation of nitrobenzene by trisynergetic attapulgite-supported nanoscale zero-valent iron–biofilm

A trisynergetic system (AFB) of nanoscale zero-valent iron (NI)–biofilm supported on attapulgite (ATP) was used to degrade nitrobenzene (NTB) in aqueous solution. We first synthesized a nanocomposite of ATP, polyvinyl alcohol, and NI as the growth carrier (AP-NI) for the biofilm. The activity of the biofilm was determined after its successful application, and the microorganisms were domesticated using NTB wastewater. The specific surface area of the AP-NI carrier was 158 m2/g, much higher than that of the traditional carrier polyvinyl alcohol (30.1 m2/g). AP-NI could be evenly distributed in water rather than settling, due to its average density of 0.647 g/m3. Additionally, the reductive efficiency of AP-NI towards NTB was about 91%, providing good support for the subsequent construction of the biofilm. Scanning electron microscopy (SEM) results indicated that the microorganisms were dominated by globular bacteria after acclimation, and could completely degrade 8 mg/L NTB in 24 h with high activity. The microbial activity depended more strongly on the choice of carbon source. Finally, polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) technology was used to analyze the microbial community structure and 16S ribosomal DNA (rDNA) sequence. The NTB degradation mechanism of the trisynergetic system revealed a mainly aerobic pathway with an iron cycle.