Experimental bioremediation cells using Poplar in combination with soil microorganisms to degrade dioxin.
Campanella, B.F., Bock, C. and Schroder, P., 2002. Phytoremediation to increase the degradation of PCBs and PCDD/Fs. Environmental Science & Pollution Research, 9: 73-85.
Johnson, T., 2008. Bioremediation and detoxification of polychlorinated dioxin contaminated environments. MMG 445 Basic Biotechnology eJournal, 4: 1-9.
Van Aken, B., Correa, P.A. and Scnoor, J.L., 2010. Phytoremediation of polychlorinated biphenyls: New trends and promises. Environmental Science & Technology, 44: 2767-2776.
Bioremediation of Organochlorine Contamination in Soil:
Case Study for Dioxin
Bioremediation is a well-established remediation technique for some organic contaminants. In situ breakdown (degradation) is promoted by a combination of fungi, bacteria and plants. This low-energy and low-impact remediation technique is proven to degrade a range of organochlorine contaminants directly in the soil including PCP, PCB and dioxin (Johnson, 2008; Van Aken et al., 2010).
Dioxin is an organochlorine contaminant where one or more chlorine atoms are attached to carbon atoms. The number and positioning of these chlorine atoms determines the relative toxicity of the contaminant (congener). During bioremediation these chlorine atoms are removed from the carbon chain (dehalogenation), or the carbon chain with chlorine attached is broken down and changed into new molecules (oxidation). Scientific evidence suggests that congeners with 1 to 6 chlorine atoms can be readily oxidised by aerobic bacteria, while more chlorinated congeners must be first oxidised by anaerobic bacteria (Campanella et al., 2002). Dehalogenation of chlorinated hydrocarbons is effected by fungi.
The processes of dehalogenation and oxidation occur in the presence of enzymes released by bacteria and fungi living in the soil. Fungi are tolerant of a wide range of environmental conditions, but bacteria grow best in a biologically active environment, such as in the root zone of plants. Fast-growing trees can be planted in the soil to promote remediation as the roots of these trees release sugars that provide sustenance for the bacteria in the soil. The optimal rate of bacteria-effected bioremediation will occur in the nutrient-rich root zone of high-biomass trees such as willow and poplar.
The Kopeopeo Canal
Western Whakatane in the Bay of Plenty. The Kopeopeo Canal runs to the right of the commercial area in the centre of the photo and historically received dioxin-contaminated run off from the saw mill to the left.
The Kopeopeo Canal is a constructed waterway on the western boundary of Whakatane, New Zealand designed to drain low lying farmlands into the Whakatane Estuary. Between 1950 and 1989, the canal received point source discharge from the NZ Forest Products, Ltd., Pinex Saw and board mills. This discharge contained wastes from the timber treatment mill where technical grade PCP was used as a wood preservative. The PCP was contaminated with dioxin and furan (PCDD/PCDFs). The legacy today is dioxin contaminated sediment at the bottom of the canal that is considered by many to be New Zealand’s most contaminated site.
The local government (Bay of Plenty Regional Council) has committed to remediating the canal. Their preferred strategy is to dredge about 40,000 cubic metres of sediment from the canal bed, to contain this in three constructed 1ha landfills, and over 15 years to degrade the organochlorine contaminants using bioremediation. The regional council chose bioremediation as the preferred remediation option based on the results of a pilot study conducted by Croesus Projects Ltd., the University of Waikato, Massey University, Environment Bay of Plenty, Earthfax Corporation (USA) and Te Runanga o Ngati Awa over 2010 and 2011.
A full-scale bioremediation project has been designed and an application for operating consent is being assessed. There is public concern over how the project will run. But this is to be expected as dioxin contamination is a serious issue for the people and communities living near the contamination. The current phase of the project illustrates how risk assessment, design, and effective communication are essential in dealing with contaminated land. Dredging is scheduled to begin in October 2014, with bioremediation to commence six-months later. At no stage during the project is there a perceived risk to the people of Whakatane, or to the environment in general. Managing the contamination is a safer option than leaving this in place for perpetuity.
Croesus’ Chris Anderson is the Science Leader for the bioremediation phase of the project. The sediment will be amended with lime, woodchips and fertiliser to better support biological growth. Once the amendments have equilibrated in the sediment, fungi and bacteria will be inoculated, and poplar trees planted. The progress of remediation will be monitored over 15 years. At the end of remediation the containment cells will be planted in native vegetation and left as markers of how bioremediation can manage even the most recalcitrant contaminants in the environment.
Croesus’ expertise in phytoremediation is complemented in this project by that of expert fungal scientist Dr. Joanne Kelly from Hamilton New Zealand. Joanne has many years of experience with the fungus-based bioremediation of organochlorine contaminants.
* Campbell Live, 3News Video
The current-day Kopeopeo canal; an issue of great community concern. Management and remediation of this site is complex.