Two phase partitioning bioreactors (TPPBs) have proved to be effective in reducing toxicity arising from high xenobiotic concentrations in biodegradation processes. The strategy utilized in TPPBs involves the use of an immiscible second phase (liquid solvent or polymer) within the bioreactor, whose function is to sequester, and gradually deliver, toxic substrate molecules to the microorganisms. In this way the microenvironment of cells is favourably influenced by the controlled partitioning of xenobiotic substrates resulting in significantly enhanced biotreatment performance. In the bioremediation of contaminated water and soils where mixed cultures are necessarily utilized, the use of polymers as the sequestering phase is extremely advantageous as polymers are completely biocompatible and inert with respect to the microbial biomass. A new opportunity for this technology in terms of environmental sustainability is to utilize waste polymeric materials as the partitioning phase. Waste polymers, in the form of automobile tires, provide an opportunity for not only reducing the initial polymer cost to near-zero, but also for utilizing a waste material for positive environmental purposes. Scrap automobile and truck tires are generated in very large quantities, on a continuous basis; for example, the estimate of used tires generated in Europe is 3.21·106 tonnes per year (European Tyre & Rubber Manufacturers' Association, http://www.etrma.org/tyres/ELTs) and in the US 2.97·106 tonnes per year (data of 2003 from US EPA http://www.epa.gov/osw/conserve/materials/tires/faq.htm). In this paper waste tires in small pieces (3-4 mm) were utilized as the sorption phase in a TPPB for the degradation of two substituted phenols 2,4 dichlorophenol (DCP) and 4-nitrophenol (4NP). These target compounds have been chosen as they are extensively used in the chemical industry (i.e. production of pesticides and herbicides) and are found in many industrial effluents. Both compounds are toxic, being characterized by EC50 values of 2.4 -40 mg/L and 64 mg/L for DCP and 4NP, respectively. The objectives of this work were to demonstrate the possibility of usefully employing and recycling a waste polymer as the partitioning phase in a TPPB, and, at the same time, to define suitable operating strategies to achieve high removal efficiencies with kinetics suitable for larger-scale treatment of the tested phenolic compounds. Sorption tests for DCP and 4NP were first performed to verify the related uptake rates. A mixed culture acclimatized to the two phenolic compounds over a 3 month period was then utilized in biodegradation tests in the TPPB reactor operated in semi-continuous mode. Biodegradation kinetics was investigated for DCP in single compound tests and for the binary mixture DCP-4NP. Experimental results demonstrate that the tires had a higher affinity for DCP, which is more toxic relative to 4NP. In single compound tests a significant reduction in DCP toxicity, and a concomitant enhancement in substrate removal efficiency (92%) is clearly seen for the TPPB case, with practically negligible biodegradation in the conventional single phase reactor. Finally, for the mixture we verified that the single phase system was not able to appreciably remove the DCP at a feed concentration of 150 mg/L for both compounds while a significant improvement is obtained in the TPPB operated with 10% v/v tires.
Re-use of automobile tires as the sequestering phase in a solid-liquid partitioning bioreactor for the biodegradation of inhibitory compounds,
2014
Abstract
Two phase partitioning bioreactors (TPPBs) have proved to be effective in reducing toxicity arising from high xenobiotic concentrations in biodegradation processes. The strategy utilized in TPPBs involves the use of an immiscible second phase (liquid solvent or polymer) within the bioreactor, whose function is to sequester, and gradually deliver, toxic substrate molecules to the microorganisms. In this way the microenvironment of cells is favourably influenced by the controlled partitioning of xenobiotic substrates resulting in significantly enhanced biotreatment performance. In the bioremediation of contaminated water and soils where mixed cultures are necessarily utilized, the use of polymers as the sequestering phase is extremely advantageous as polymers are completely biocompatible and inert with respect to the microbial biomass. A new opportunity for this technology in terms of environmental sustainability is to utilize waste polymeric materials as the partitioning phase. Waste polymers, in the form of automobile tires, provide an opportunity for not only reducing the initial polymer cost to near-zero, but also for utilizing a waste material for positive environmental purposes. Scrap automobile and truck tires are generated in very large quantities, on a continuous basis; for example, the estimate of used tires generated in Europe is 3.21·106 tonnes per year (European Tyre & Rubber Manufacturers' Association, http://www.etrma.org/tyres/ELTs) and in the US 2.97·106 tonnes per year (data of 2003 from US EPA http://www.epa.gov/osw/conserve/materials/tires/faq.htm). In this paper waste tires in small pieces (3-4 mm) were utilized as the sorption phase in a TPPB for the degradation of two substituted phenols 2,4 dichlorophenol (DCP) and 4-nitrophenol (4NP). These target compounds have been chosen as they are extensively used in the chemical industry (i.e. production of pesticides and herbicides) and are found in many industrial effluents. Both compounds are toxic, being characterized by EC50 values of 2.4 -40 mg/L and 64 mg/L for DCP and 4NP, respectively. The objectives of this work were to demonstrate the possibility of usefully employing and recycling a waste polymer as the partitioning phase in a TPPB, and, at the same time, to define suitable operating strategies to achieve high removal efficiencies with kinetics suitable for larger-scale treatment of the tested phenolic compounds. Sorption tests for DCP and 4NP were first performed to verify the related uptake rates. A mixed culture acclimatized to the two phenolic compounds over a 3 month period was then utilized in biodegradation tests in the TPPB reactor operated in semi-continuous mode. Biodegradation kinetics was investigated for DCP in single compound tests and for the binary mixture DCP-4NP. Experimental results demonstrate that the tires had a higher affinity for DCP, which is more toxic relative to 4NP. In single compound tests a significant reduction in DCP toxicity, and a concomitant enhancement in substrate removal efficiency (92%) is clearly seen for the TPPB case, with practically negligible biodegradation in the conventional single phase reactor. Finally, for the mixture we verified that the single phase system was not able to appreciably remove the DCP at a feed concentration of 150 mg/L for both compounds while a significant improvement is obtained in the TPPB operated with 10% v/v tires.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
