Professor of Environmental Engineering University of Cincinnati Cincinnati, Ohio
Emissions of hydrocarbons such as styrene and toluene are among the largest volume produced contaminants in industrial facilities in the world. Styrene and toluene are commonly used as fuels and solvents to further produce polymers, resins, plastics, inks, and paints. Due to their widespread presence in various environmental forms and their substantial toxicity, their treatment is critical to protect the public health. In a previous work we have investigated the effect of biosurfactants, rhamnolipids, in improving toluene hydrophobicity. It is stipulated that a mixture of styrene and toluene is expected to be a more challenging scenario in terms of the VOCs biodegradability. Therefore, the aim of this study is to investigate the effect of rhamnolipids on styrene removal as well as a mixture of styrene and toluene. Hence, this study will be more focused on a co-treatment approach. Two lab-scale biotrickling filters (BTFs) inoculated with fungi, hereby designated as “BTF-A” and “BTF-B”, were run simultaneously to purify styrene as sole carbon source, and a mixture of styrene and toluene, respectively. In efforts to explore solutions of styrene and toluene hydrophobicity, low-concentration of a lipopeptide-type biosurfactant extracellularly produced by gram-negative bacteria Pseudomonas aeruginosa was added and mixed with the nutrient composition feeding the BTFs. BTF-A started up with phase I with an influent concentration of 133.5 ppmv of styrene, while BTF-B received similar concentrations of styrene and toluene at a ratio of 1:1 by concentration for 3 weeks for as a stabilization period. Furthermore, the BTFs received an increasing step-change in influent concentration (i.e., phase II was set up at 269 ppmv). Inlet loading rates were stretched beyond industry levels to examine the flexibility of the BTFs in response to shock loads at empty bed residence time of 60 seconds. The BTFs were run at room temperature and received nutrient and buffer feed (pH 4) at a rate of 1.5 L d-1. Excessive biomass growth was controlled by stagnation to maintain a constant pressure drop within the BTFs to reduce channeling and provide a constant gaseous flow. Experimental results have shown that the removal efficiency of BTF-A is over the 90% range for the phases studied up to date, while BTF-B which received the VOCs mixture has demonstrated a drastic decline in removal efficiency with the increase in VOCs inlet loading rates. This may conclude that the co-treatment experiment employed in BTF-B showed a poor performance for the synergistic bioavailability for both VOCs than BTF-A. Investigations under higher EBRTs could lead to an improved performance.
