Bioremediation of contaminated water: use of microbial biofilms on innovative biopolymeric scaffolds

The contamination of soil, water, air and marine sediments is one of the major cause of alteration of environmental quality, that has also negative effects on human health. Chemically heterogeneous compounds have particular importance, due to their massive use in the civil and industrial fields and inappropriate disposal procedures, they are generally toxic and resistant to degradation, causing health problems also for the ‘human being’. Among the different types of environmental contaminants, high molecular weight hydrocarbons (HCs), polycyclic aromatic hydrocarbons (PAHs) and chlorinated solvents have been given top priority by the US-EPA and EU environmental agencies. A promising technology for the treatment of contaminated site is based on biodegradation of pollutants, carried out by microbial species endowed with specific catabolic capacities. In the last few years, the application of biotechnological processes that exploits HC-degrading biofilm, with the objective of solving environmental pollution problems, is rapidly growing. This doctoral research aimed to develop and evaluate innovative bioremediation strategies using microbial biofilms immobilized on biodegradable biopolymeric scaffolds, targeting both petroleum hydrocarbons (HCs) and 1,2-dichloroethane (1,2-DCA). Three highly efficient HC-degrading strains (Alcanivorax sp. AU3AA7, Gordonia sp. SoCg., Nocardia sp. SoB.) were immobilized on electrospun polylactic acid (PLA) and polycaprolactone (PCL) membranes (produced by electrospinning), (Chapter II). These biofilm–membrane systems demonstrated high adhesion, biofilm proliferation, and higher biodegradation performance, between 13% and 35% of Total Petroleum Hydrocarbons (TPHs) removal and increased alkB gene, expression compared to planktonic cells. The bacterial strains were able to attach to the PLA and PCL membranes reaching high proliferation and biofilm formation within the whole structure remaining active for up to 30 days. The ability to survive in a stress over time condition, simulating storage effects, for another 15 days of incubation (biofilm exposed to hexadecane-saturated air) was also tested. The air exposed biofilms preserved a structural organization of biofilm comparable to those maintained in liquid culture. The HC-degrading biofilm immobilization is a promoting factor for biodegradation and a the novel ready to use systems be developed for promising tools bioremediation. Chlorinated solvents are synthetic organohalide chemicals frequently found as contaminants of groundwater and soil, due to their widespread use in several industrial processes and improper disposal methods. These compounds pose serious health threats because of their toxic and sometimes carcinogenic effects. Among these compounds, 1,2-dichloroethane (1,2-DCA) is one of the most common aquifer contaminants, considered toxic and classified as a possible human carcinogen. Biodegradation of chlorinated aliphatic hydrocarbons (CAHs), that is carried out by specialized bacteria under anaerobic and aerobic conditions. Aerobic dechlorination of chlorinated compounds is less well understood than anaerobic dechlorination, several studies have begun to elucidate the relevant pathways and enzymes.Novel aerobic 1,2-DCA-degrading consortia (Chapter IV) were isolated from a contaminated aquifer previously studied by our group. Despite predominantly anaerobic conditions, aerobic dechlorinating bacteria were enriched and molecularly characterized, to be exploited in bioremediation strategies based on degrading biofilms immobilized on biodegradable scaffolds.Selected consortia, positive for the dhlA gene and dominated by Ancylobacter spp., achieved complete degradation of 1,2-DCA (1000 ppm) within 4–7 days. When immobilized on PLA scaffolds (Chapter V), these consortia retained their biodegradation capacity, showing potential for reuse and application as bioremediation devices in engineered systems. The ability of biopolymeric membranes and scaffolds to adsorb organic contaminants increases the bioavailability of the contaminant for the degrading bacteria. The combined use of biodegradable scaffolds and specialized microbial cultures enhances the bioavailability of pollutants and provides a promising foundation for biofilm-based technologies. These systems show strong potential for application in engineered settings and enhanced bioremediation strategies such as bioreactors and permeable reactive barriers (PRBs) for the treatment of contaminated water, air and soil.