Research Goals: The primary objective of this research is to investigate the impacts of heavy metals on the biodegradation of PAHs using biofilm processes. A porous sand media will be developed to simulate a soil contaminated by PAHs. The study will be divided into two parts: one is to observe the macro phenomena occurring when heavy metals are introduced into a biofilm process actively bioremediating PAHs. The other is to investigate the fundamental principles of these phenomena, which will focus on what is happening inside the biofilm.

Overview: Polycyclic aromatic hydrocarbons (PAHs) are chemicals made up of two or more fused benzene rings and/or pentacyclic moieties in linear, angular, and cluster arrangements. They are naturally produced through forest combustions and volcano eruptions. As modern industry has developed, these compounds are also produced by human activities. They are carcinogenic and persistent in natural conditions. Mandy studies focusing on PAH bioremediation have been carried out because of the resistance of PAHs in traditionally biological treatment processes.

Heavy metal contamination is another important product of human industrial activities. They could be produced simultaneously with PAH in mining, ore refinement, and coal combustion, etc. Heavy metals will not only influence human health, but also will restrain microorganism activity, and are resistant to traditional treatment processes.

In this study, biofilms that grow on porous media surfaces are used to degrade organic compounds in soil-groundwater systems. A bio-barrier process should be developed based on the study of biofilms to enhance the bioremediation of PAH contaminated soil and groundwater systems.

This research will study the possibility and performance of biofilm process in the biodegradation of PAHs in the presence of heavy metals. A porous sand media will be used to simulate a contaminated soil and its biofilm. Biofilms will be developed on the surface of sand in a glass column. In the presence of heavy metals, bioavailability and biodegradation of PAHs, physical, chemical, and biological properties of biofilms and the spatial variability of these properties will be investigated.

Progress to Date:
Glass columns and flow cells have been designed and manufactured. Columns and flow cells have been packed with a mixture of sands and activated sludge, biofilms have been developed. Naphthalene is used as carbon source, sodium acetate is used as alternative substrate. Cadmium is selected as the heavy metal.

Application of Knowledge:
Bioremediation of contaminated soil and groundwater. Biofilm processes in waste treatment. PAH degradation pathway. Heavy metal distribution in soil and groundwater. Impact of heavy metal on microorganisms.

Future Directions: Instead of naphthalene, more complicated PAHs will be used in this study. Instead of cadmium, lead and mixtures of cadmium and lead will be studied.

Techniques Incorporated:
Heavy metals: atomic adsorption spectrometry, inductively coupled plasma spectrometry
PAHs: gas chromatography, gas chromatography/mass spectrometry
Biofilm properties: scanning confocal laser microscopy, micro-slicing, and micro-electrodes
Extracellular Polymeric Substances: total carbonate, total protein methods
Viable biomass: total lipid phosphate method

Keywords:
PAHs
Biodegradation
Biofilm
Heavy metals