Fungal removal of gaseous hexane in biofilters packed with poly(ethylene carbonate) pine sawdust or peat composites

Abstract

The removal of volatile organic compounds (VOC) in biofilters packed with organic filter beds, such as peat moss (PM) and pine sawdust (PS), frequently presents drawbacks associated to the collapse of internal structures affecting the long-term operation. Poly(ethylene ether carbonate) (PEEC) groups grafted to these organic carriers cross linked with 4,4'-methylenebis(phenylisocyanate) (MDI) permitted fiber aggregation into specific shapes and with excellent hexane sorption performance. Modified peat moss (IPM) showed very favorable characteristics for rapid microbial development. Water-holding capacity in addition to hexane adsorption almost equal to the dry samples was obtained. Pilot scale hexane biofiltration experiments were performed with the composites after inoculation with the filamentous fungus Fusarium solani. During the operation of the biofilter under non-aseptic conditions, the addition of bacterial antibiotics did not have a relevant effect on hexane removal, confirming the role of fungi in the uptake of hexane and that bacterial growth was intrinsically limited by an adequate performance of the composites. IPM biofilter had a start-up period of 8-13 days with concurrent CO(2) production of approximately 90 g m(-3) h(-1) at day 11. The final pressure drop after 70 days of operation was 5.3 mmH(2)O m(-1) reactor. For modified pine sawdust (IPS) packed biofilter, 5 days were required to develop an EC of about 100 g m(-3) h(-1) with an inlet hexane load of approximately 190 g m(-3) h(-1). Under similar conditions, 12-17 days were required to observe a significant start-up in the reference perlite biofilter to reach gradually an EC of approximately 100 g m(-3) h(-1) at day 32. Under typical biofiltration conditions, the physical-chemical properties of the modified supports maintained a minimum water activity (a(w)) of 0.925 and a pH between 4 and 5.5, which allowed the preferential fungal development and limited bacterial growth.