Biodegradation of toluene vapor in coir based upflow packed bed reactor by Trichoderma asperellum isolate

Effect of surfactin on removal of semi-volatile organic compound: Emphasis on enhanced biofiltration performance

The performance of a lab-scale biotrickling filter (BTF) inoculated with a mixed fungal consortium was investigated for the simultaneous abatement of 2-ethylhexanol; a hydrophobic semi-volatile organic compound (SVOC), and propylene glycol monomethyl ether (PGME). The BTF performance was investigated in the presence of lipopeptide-type biosurfactant, surfactin. The effect of surfactin on the removal efficiency and elimination capacity was examined at stretched inlet loading rates (LR): 1.04 to 15.7 and 3.2-48 g m^-3 h^-1 of PGME and 2-ethylhexanol, respectively. Seeding the BTF with 50 mg L^-1 of surfactin maintained high and consistent removal efficiencies of PGME and 2-ethylhexanol up to LRs of 15.7 and 32 g m^-3 h^-1, with removal efficiencies of 98.5 and 99%, respectively. Once the LR of 2-ethylhexanol increased to 48 g m^-3 h^-1, a substrate inhibition was observed, accompanied by a sudden decrease in removal efficiency from 99.2 to 62.3%. At the same LR, the BTF performance was improved by reseeding 100 mg L^-1 of surfactin, hence, reinstated the removal efficiency of 2-ethylhexanol to 92.7% and achieving a maximum elimination capacity of 44.5 g m^-3 h^-1. This enhanced SVOC uptake rate was further confirmed by a considerable increase in reaction rate constant from 0.005 to 0.017 s^-1. A batch study was also conducted at the end of the experimental run to better understand the correlation between surfactin concentrations and the time-dependent partition coefficient of 2-ethylhexanol. Biofilm microbial community structure revealed relative abundancy of 72 and 28% of Trichoderma asperellum and Fusarium solani, respectively. The findings of this study show for the first time that the removal of a semi-VOC such as 2-ethylhexanol is feasible in the presence of surfactin and hence improving the bioavailability of hydrophobic semi-VOC.

Fungal elimination of toluene vapor in one- and two-liquid phase biotrickling filters: Effects of inlet concentration, operating temperature, and peroxidase enzyme activity

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 CO₂ in OLP-BTF (1.38 mol CO₂/mole toluene) in comparison to TLP-BTF (0.67 mol CO₂/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.

The impact of environmental parameters on the conversion of toluene to CO2 and extracellular polymeric substances in a differential soil biofilter

The fraction of pollutant converted to CO₂ versus biomass in biofiltration influences the process efficacy and the lifetime of the bed due to pressure drop increases. This work determined the relative quantitative importance and potential interactions between three critical environmental parameters: toluene concentration (Tol), matric potential (ψ) and temperature (T) on % CO₂, elimination capacity (EC) and the production rate of non-CO₂ products. These parameters are the most variable in typical biofilter operation. The data was fit to a non-linear model of the form y=a(Tol)^bT^cψ^d. A rigorous carbon balance (100.5 ± 7.0%) tracked the fate of degraded toluene as CO₂ and non-CO₂ carbon endpoints. The % CO₂ mineralization varied from (34-91%) with environmental parameters: temperature (20-40 °C), matric potential, (-10 to -100 cm_H2O) and residual toluene, (20-180 ppm). The highest conversion to CO₂ was at the wettest conditions (-10 cm_H2O) and lowest residual toluene concentration (18 ppm). Matric potential had twice the impact of toluene concentration on % CO₂, while temperature had less impact. The elimination capacity varied from 11 to 50 g_C⋅m^-3h^-1 and was highest at 40 °C, the wettest conditions with limited impact by toluene concentrations. Temperature increased the EC and non-CO₂ production rates strongly while matric potential and toluene concentration had less influence (4x - 10x less). This study illustrated the quantitative significance and simultaneous interaction between critical environmental parameters on carbon endpoints and biofilter performance. This kind of multivariable parameter study provides valuable insights which can address performance and clogging issues in biofilters.

Improved peroxidase-mediated biodegradation of toluene vapors in the moving-bed activated sludge diffusion (MASD) process using biosurfactant-generating biomass stimulated with H2O2

Two strategies were attempted to improve the biodegradation and mineralization of toluene vapors in the activated sludge diffusion (ASD) process using biosurfactant-generating Pseudomonas spp. and Bacillus spp. mixture. Different operational parameters including toluene concentration, superficial air velocity, biomass concentration, moving-media insertion and H₂O₂ were evaluated on toluene removal in the ASD process within 550 days of operation. It was found that complete biodegradation and 79.8% mineralization of toluene vapors at inlet loading rate of 144 g/m³.h could be achieved in the ASD process by inserting moving media (MASD) at a volume ratio of 20% along with stimulation of bacteria with H₂O₂. The concentration of biosurfactant and peroxidase generated in the integrated process (H₂O₂-stimulated MASD reactor) was 3.7 and 2.5 times of that in the conventional ASD process. The maximum toluene elimination capacity obtained in the H₂O₂- stimulated MASD process was 285 g/m³.h at an inlet loading rate of around 430 g/m³.h. Accordingly, H₂O₂-mediated MASD process could be a promising technique for efficient biodegradation and mineralization of aromatic hydrocarbons in the contaminated air streams.

A modified biotrickling filter for nitrification-denitrification in the treatment of an ammonia-contaminated air stream

A conventional biotrickling filter for airborne ammonia nitrification has been modified, by converting the liquid sump into a biological denitrifying reactor. The biotrickling filter achieves an average ammonia removal efficiency of 92.4 %, with an empty bed retention time (EBRT) equal to 36 s and an average ammonia concentration of 54.7 mg Nm^-3 in the raw air stream. The denitrification reactor converts ammonia into inert gas N₂, in addition to other important advantages connected to the alkaline character of the biochemical pathway of the denitrifying bacteria. Firstly, the trickling water crossing the denitrification reactor underwent a notable pH increase from 7.3 to 8.0 which prevented the acidic inhibition of the nitrifying bacteria due to the buildup of nitric and nitrous acids. Secondly, the pH increase created the ideal conditions for the autotrophic nitrifying bacteria. The tests proved that an ammonia removal efficiency of above 90 % can be achieved with an EBRT greater than 30 s and a volumetric load lower than 200 g NH₃ m^-3 day^-1. The results of the biofilm observation by using a scanning confocal laser microscope are reported together with the identification of degrading bacteria genera in the biotrickling filter. The efficiency of the plant and its excellent operational stability highlight the effectiveness of the synergistic action between the denitrification reactor and the biotrickling filter in removing airborne ammonia.