Contents lists available at ScienceDirect Journal of Environmental Management journal homepage: www.elsevier.com/locate/jenvman Research article Fungal elimination of toluene vapor in one- and two-liquid phase biotrickling filters: Effects of inlet concentration, operating temperature, and peroxidase enzyme activity Ali Yousefinejad, Seyed Morteza Zamir * , Mohsen Nosrati Biotechnology Group, Faculty of Chemical Engineering, Tarbiat Modares University (TMU), PO Box: 14115-143, Iran ARTICLE INFO Keywords: Biofilm CO 2 production rate Enzymatic activity Ligninolytic enzyme Mass transfer limitation T-test ABSTRACT In this study, performance of biotrickling filters (BTFs) inoculated with fungus Phanerochaete chrysosporium at 30 °C and 40 °C in the absence and presence of silicone oil (10% v/v) was investigated. Removal of toluene was carried out at empty bed residence time (EBRT) of 1 min and at inlet concentrations of 0.5–4.4 g m -3 and 0.5–24.7 g m -3 for one-liquid phase (OLP-BTF) and two-liquid phase BTF (TLP-BTF), respectively. In general, at 40 °C, removal efficiencies (REs) > 80% were obtained in OLP-BTF for the inlet toluene concentrations < 2.5 g m -3 , and REs > 70% were obtained for concentrations < 18 g m -3 in TLP-BTF. Based on the balanced equation for biodegradation, fungal respiration produced more CO 2 in OLP-BTF (1.38 mol CO 2 /mole toluene) in comparison to TLP-BTF (0.67 mol CO 2 /mole toluene). In other words, the presence of oil enhanced microbial growth due to the increase of hydrophobic substrate bioavailability. The activity of extracellular ligninolytic manganese peroxidase (MnP) enzyme produced by the fungal culture was detected in the range of 27.6–71.6 U L -1 (μmol min -1 L -1 ) at 40 °C in TLP-BTF, while no enzymatic activity was detected in OLP-BTF. 1. Introduction Volatile organic compounds (VOCs) emitted from various industries can affect public health and environment because of the toxicity and stability. Toluene is assumed as a hydrophobic VOC and an important environmental pollutant that can cause human carcinogen (Béchohra et al., 2016; Guillerm et al., 2017). Biofilters (BFs) and biotrickling fi- lers (BTFs), designed for the treatment of waste air containing volatile organic compounds (VOCs), are not only cost-effective, but also en- vironment-friendly and suitable for high inlet loading rates (ILRs) and low concentrations of pollutants (Ferdowsi et al., 2017; Bordoloi and Gostomski, 2019). In BFs and BTFs, VOCs are mineralized to CO 2 , water, and biomass by appropriate biocatalysts such as bacteria or fungi (Cheng et al., 2016a). In BTFs, a continuous trickling liquid is re- circulating through the packing materials in order to provide nutrients for the immobilized microbial growth. Thus, better control of pressure drop, nutrient concentration, and pH can be achieved due to the pre- sence of circulating liquid phase in the BTF (Wu et al., 2018). There- fore, in comparison to the conventional BFs, BTFs can be more con- trollable in terms of pH and temperature, and can also be more capable of degrading hydrophilic compounds (Alinejad et al., 2017; Boojari et al., 2019a). In spite of application of BTFs for waste-gas treatment from many years ago, it still is considered as an innovative technology with new application areas every year (Oyarzun et al., 2019). However, the rate of mass transfer for hydrophobic compounds such as toluene is reduced due to the continuous falling layer of aqueous phase in the BTFs; therefore, high elimination capacities (ECs > 150 g m -3 h -1 ) cannot be obtained when encountering high inlet loading rates (ILRs > 200 g m -3 h -1 ) of hydrophobic VOCs (Ferdowsi et al., 2017; Darracq et al., 2012a; Han et al., 2019). A non-biodegradable organic solvent (e.g. silicone oil) is added to the trickling liquid to form a two-phase liquid to overcome the mass transfer limitation problem (San-Valero et al., 2018a). The organic solvent, known as non-aqueous phase (NAP), can improve the poor aqueous solubility of the hydrophobic pollutants in the liquid phase (San-Valero et al., 2018a; Gopinath et al., 2016). The NAP can also increase the mass transfer rate of oxygen due to its affinity to oxygen. The other feature of NAP is that it can prevent the microorganism to be encountered to high concentrations of VOC that may increase the risk of microbial inhibition (San-Valero et al., 2018b). For example, at ILR of 120 g m -3 h -1 , EC of 70 g m -3 h -1 was obtained for the styrene re- moval in a one-liquid phase BTF (OLP-BTF), while EC increased to 110 g m -3 h -1 for a two-liquid phase BTF (TLP-BTF) in the presence of 5% v/v silicone oil (Zamir et al., 2015). Also, Lebrero et al. (2014) https://doi.org/10.1016/j.jenvman.2019.109554 Received 21 February 2019; Received in revised form 30 August 2019; Accepted 7 September 2019 * Corresponding author. E-mail address: zamir@modares.ac.ir (S.M. Zamir). Journal of Environmental Management 251 (2019) 109554 0301-4797/ © 2019 Elsevier Ltd. All rights reserved. T