Although microbial transformation of PCBs has been the subject of intense study over the past 25 years, it is now apparent that the use of simplistic remediation approaches, based on conventional bioreactor and landfarming strategies, will not be successful. One of the primary barriers to effective PCB bioremediation is the limited availability of PCBs to microbial populations. PCBs are extremely hydrophobic compounds, which results in their low equilibrium solubilities and slow rates of desorption from solid phases. These physical/chemical barriers may contribute to incomplete bioremediation of PCB-contaminated sites and the inability to reach target PCB concentrations.
To overcome such limitations, we have proposed the use of surfactants to increase the equilibrium solubility and mass transfer rate of PCBs into the aqueous phase. Three commercially-available surfactants were selected for study; Tween 80, Witconol SN-120, and Tergitol NP-15. The research is funded as part of the Strategic Environmental Research and Development Program (SERDP) Federal Integrated Biotreatment Research Consortium (FIBRC).
Specific objectives are as follows:
Both NY05 and VP44 exhibited rapid growth on biphenyl alone, reaching an optical density of 2-3 after 24 hours. These findings are consistent with the observed tolerance of NY05 to extremely high concentrations (up to 1000 ppm) of Aroclor 1242. However, neither NY05 or VP44 grew in solutions containing Witconol SN-120, Witconol SN-120+biphenyl and Witconol SN-120+4-chlorobiphenyl. These data indicate that Witconol SN-120 cannot be used as a substrate by NY05 and VP44, and that Witconol SN-120 inhibits utilization biphenyl and 4-chlorobiphenyl. These results suggest that Witconol SN-120 is unsuitable for use in enhanced PCB bioremediation systems.
Growth of NY05 and VP44 on biphenyl alone, Tween 80, Tween 80+biphenyl, and Tween 80+4-chlorobiphenyl were virtually the same. A slight dependence on surfactant concentration was observed when the concentration of Tween 80 was increased from 125 ppm to 5,575 mg/L. Growth of NY05 on biphenyl was not influenced by the presence of Tween 80 at concentrations ranging from 1,200 to 2,500 mg/L of surfactant. Similar trends were observed for VP44. These data indicate that Tween 80 can be readily utilized as a food source and does not inhibit growth on biphenyl. However, Tween 80 could be utilized as preferential substrate, and thus, may not be suitable for PCB bioremediation.
For both NY05 and VP44, no growth was observed on Tergitol NP-15 alone over concentrations ranging from 187 mg/L to 4,000 mg/L. This behavior was anticipated given the reported difficulties in degrading ethoxylated alkylphenol surfactants. However, the observed growth of NY05 and VP44 on biphenyl and 4-chlorobiphenyl in the presence of Tergitol NP-15 at concentrations up to 4,300 mg/L, was not anticipated. These finding suggest that Tergitol NP-15 is not be used as a preferential growth substrate by PCB-degrading bacteria and that the presence of Tergitol NP-15 will not inhibit growth on PCB congeners. For these reasons, Tergitol NP-15 may be an ideal candidate for use in PCB bioremediation systems. Additional experiments are currently underway to quantify the transformation of selected PCB congeners by NY05 and VP44 in the presence of Tergitol NP-15 and Tween 80.