ARTICLE pubs.acs.org/IECR
Natural-Fiber-Reinforced Composite Treated with Polyamines Used as a Support for the Biodegradation and Adsorption of Toluene Olga B. Gutierrez Acosta† and Vladimir A. Escobar Barrios* Division de Ciencias Ambientales, Instituto Potosino de Investigacion Científica y Tecnologica, Camino a la Presa San Jose 2055, Lomas 4a Seccion, CP 78210, San Luis Potosí, SLP, Mexico ABSTRACT: The effect of the addition of two different polyamines into a foamed polymeric matrix with embedded natural fiber, to synthesize biocomposites, was studied during the degradation of toluene in batch experiments. The synthesized biocomposites were able to adsorb and facilitate the degradation of toluene by micro-organisms attached in the biocomposite matrix, at a high extent (80%), in a very short period of time (1 day). The adsorption and biodegradation processes were simultaneous. The molecular weight of polyamine had a slight effect on toluene adsorption, with the lower-molecular-weight polyamine being more favorable for the adsorption process. However, the biocomposites, with polyamines, were not able to carry out the complete biodegradation of toluene during the term of experiment (26 days). The absence of polyamine in the biocomposite had a dramatic effect on adsorption and biodegradation of toluene, improving both processes and showing a CO2 production that is 730% higher than biocomposites synthesized with polyamine, because of a toxic and/or barrier effect of polyamine. This biocomposite, synthesized without polyamine, was able to carry out the complete biodegradation during the first 5 days, and it had adequate cyclic performance.
1. INTRODUCTION Toluene is widely used in diverse industries as a solvent, and usually it is emitted into air or water without any treatment, which promotes adverse effects on human health and the environment. Therefore, treatment of the toluene emissions is essential.1,2 Biofiltration is an attractive treatment alternative for solvents, since it transforms the contaminant, by micro-organisms, to components (water vapor and carbon dioxide), which are not as harmful as the solvent itself. This technique represents an advantageous alternative from an economical and technological point of view, when compared to physicochemical treatments. In order to improve the performance of the biodegradation of solvents, it has been recognized that micro-organisms must be supported.3,4 In this sense, several supports have been proposed, from natural to synthetic materials. Natural materials are a source of nutrients for the micro-organisms. However, they can be degraded by micro-organisms and became weak in terms of mechanical properties.57 Mineral materials have been used as packing materials, because they are not degraded by microorganisms and have good mechanical resistance, but they do not serve as a source of nutrients.8 The synthetic materials do not act like a nutrient source for the micro-organisms, but they do have adequate physical characteristics. Polyurethane has been the object of several studies, since it has advantages such as porosity, water holding capacity, and bulk density.911 Nevertheless, polyurethane usually is hydrophobic and must be modified to increase its hydrophilic character, since micro-organisms need humidity to favor their growth, among other conditions such as pH, temperature, and contaminant load.12,13 The natural fibers can adsorb water several times their own weight. Thus, they facilitate the water retention of fiber-containing r 2011 American Chemical Society
composites, and they are not easily degraded by micro-organisms as other natural materials, because of their complex structure. Natural fibers have been studied in order to adsorb organic vapors, such as toluene.6 In addition, low-molecular-weight amines have recently been added to natural fibers in order to enhance contaminant adsorption, but they could also serve as source of nitrogen for microorganisms.1416 Since the pollutant load can vary with time due to industrial activity, it is important to control the load in order to have a constant feed of pollutants to micro-organisms and thus maintain their degradation capacity. In order to deal with problems of variations in the inlet load, some alternatives have been proposed, such as the use of a previous adsorption step or the use of two-phase partitioning bioreactors.15,17,18 The present study propose the synthesis of biocomposites, based on natural fiber and polymeric matrix, and supplemented with two polyamines of different molecular weight, which were added during polyurethane prepolymer polymerization in order to offer a source of nutrients for micro-organisms. The aim of the study was to investigate the adsorption of toluene by biocomposites based on a natural fiber and synthetic polymeric matrix, since it has been reported that such materials, fiber and polymeric matrix, are able to adsorb contaminants like toluene.59,11 Therefore, it is considered that such biocomposite could keep a constant toluene feed to the micro-organism and, consequently, to accelerate the toluene biodegradation. Received: August 12, 2010 Accepted: May 6, 2011 Revised: May 5, 2011 Published: May 06, 2011 7572
dx.doi.org/10.1021/ie101712c | Ind. Eng. Chem. Res. 2011, 50, 7572–7578
Industrial & Engineering Chemistry Research
2. MATERIALS AND METHODS 2.1. Materials. The polymeric matrix is based on prepolymer polyurethane with an isocyanate free content of 13% w/w (Bayer MaterialScience, Leverkusen, Germany). The natural fiber was provided by Tecnología Ambiental (San Luis Potosí, Mexico). The fiber was obtained from dried and chopped hyacinths and it has an average length of 2 mm. The polyamines were provided by BASF (Ludwigshafen, Germany), the polyamine named A-1 has a molecular weight of 2000 g/mol with a viscosity of 12 000 mPa s at 20 °C and the polyamine named A-2 has a molecular weight of 800 g/mol with a viscosity of 3000 mPa s at 20 °C; both polyamines have primary, secondary, and tertiary amine groups in their structures and a water content of
