Biodegradation of 4-nitrophenol in a two-phase system operating with polymers as the partitioning phase

The present study has demonstrated the enhanced performance of a two-phase bioreactor, operating with polymers as a partitioning phase, as an alternative to both single phase biotreatment and to the use of an immiscible organic solvent partitioning phase, to deliver a toxic substrate (4-nitrophenol, or 4NP) to a microbial consortium in batch and repeated batch mode. Three commercial polymers were tested, Hytrel, Tone, and Elvax, and were shown to have superior properties related to the use of a consortium, including complete biocompatibility with the biomass and nonbiodegradability. Repeated kinetic tests performed with short reaction times demonstrated the accumulation of 4NP within the polymers in the range of 6-8 mg/g polymer, which reduced polymer performance in subsequent batch operations. Hytrel gave the best performance with residuals of up to 4 mg/g polymer showing no reduction in subsequent use, while for the other polymers a 4NP value lower than 2 mg/g polymer was required to have acceptable performance during repeated polymer use. Polymer reuse without affecting the process efficiency was confirmed with regeneration tests. A conventional methanol extraction method, as well as biological regeneration of the polymers by prolonged contact with the biomass, were assessed for their ability to remove the residual 4NP. Parallel kinetic tests performed with newand regenerated polymers showed a complete overlap of the 4NP concentration profiles indicating that a simple biological regeneration method provides a means of completely restoring polymer performance for repeated batch operation.