Project 5 – Microencapsulation Delivery Vehicles for the Implementation of Precision Bioremediation at PAH-Contaminated Superfund Sites

Project Leaders

Objective and Importance of Research

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous and toxic contaminants and are often challenging to clean up. Conventional clean-up methods such as soil excavation or dredging are expensive, and can impact local ecosystems. Bioremediation using local, introduced, and altered microorganisms such as bacteria and fungi, holds promise as a lower impact alternative. This project will build on previous work to study strategies to improve the long-term survival of introduced microorganisms and their effectiveness at breaking down PAHs. The project will also investigate the chemicals formed from degrading PAHs and any unintended impacts they may have on other contaminants on site such as metals.

Summary

Polycyclic aromatic hydrocarbons (PAHs) are contaminants of great concern due to their toxic, mutagenic and carcinogenic properties that are commonly encountered at Superfund sites. Due to their chemical characteristics, PAHs tend to be highly hydrophobic and recalcitrant, making them challenging targets for remediation. PAH- impacted sites are also frequently enriched with toxic metals from related industries, and such mixtures require engineering solutions that effectively target PAHs while minimizing deleterious environmental impacts on co- contaminants. Treatments in multi-contaminant settings are particularly challenging because bioremediation strategies aimed at PAHs can introduce environmental conditions such as oxic microniches that may enhance the leaching potential and bioavailability of metals. Because of these challenges, site managers often resort to drastic remediation approaches such as soil excavation or dredging, which can have significant negative long- term impacts on local ecosystems. In situ bioremediation has been widely studied as an alternative approach with minimal ecological disruption.

During the last funding period, the team developed a generalizable framework for the precision bioremediation of PAHs that harnesses in situ cross-kingdom microbial interactions. They created a library of fungal and bacterial strains that could work cooperatively to breakdown PAHs. Yet, while strain selection is a pivotal decision to be made for the effectiveness of the amended microbes, the observed transience of some augmented strains after inoculation can significantly reduce the long-term effectiveness of bioremediation. Thus, a particular challenge that remains to be solved is the long-term survival and activity of augmented exogenous strains under complex site conditions. Herein, this project addresses this challenge by developing microbial encapsulation delivery vehicles that enable targeted delivery and increased fitness of key microbial strains for the implementation of precision bioremediation. The permeability of the microcapsule, alongside the protective separation of the internal organisms from the external environment, makes microcapsules attractive for deployment to natural environments and for the implementation of precision bioremediation.

The scientists hypothesize that the use of microcapsules will improve delivery, viability and fitness of the augmented microbes thereby improving PAH biodegradation.

Project Aims

  1. Optimize microcapsule synthesis for delivery to soil/sediment sites, sorption of target PAHs, and growth/function of encapsulated microbes.
  2. Develop site-specific encapsulated microbial consortia of PAH degraders and compare to pure cultures for PAH degradation.
  3. Investigate unintended impacts of the microencapsulated bioaugmentation strategy through evaluation of PAH degradation products and geochemical transformations of co-contaminant metals in Superfund-relevant conditions