The operating performance of a biotrickling filter with Lysinibacillus fusiformis for the removal of high-loading gaseous chlorobenzene

Study on Gaseous Chlorobenzene Treatment by a Bio-Trickling Filter: Degradation Mechanism and Microbial Community

Large-flow waste gas generated from the pharmaceutical and chemical industry usually contains low concentrations of VOCs (volatile organic compounds), and it is also the key factor that presents challenges in terms of disposal. To date, due to the limitations of mass transfer rate and microbial degradation ability, the degradation performance of VOCs using the biological method has not been ideal. Therefore, in this study, the sludge from a chlorobenzene-containing wastewater treatment plant was inoculated into our experimental bio-trickling filter (BTF) to explore the feasibility of domestication and degradation of gaseous chlorobenzene by highly active microorganisms. The kinetics of its mass transfer reaction and microbial community dynamics were also discussed. Moreover, the main process parameters of BTF for chlorobenzene degradation were optimized. The results showed that the degradation effect of chlorobenzene reached more than 85% at an inlet concentration of chlorobenzene 700 mg·m−3, oxygen concentration of 10%, and an empty bed retention time (EBRT) of 80 s. The mass transfer kinetic analysis indicated that the process of chlorobenzene degradation in the BTF occurred between the zero-stage reaction and the first-stage reaction. This BTF contributed significantly to the biodegradability of chlorobenzene, overcoming the limitation of gas-to-liquid/solid mass transfer of chlorobenzene. The analysis of the species diversity showed that Thermomonas, Petrimona, Comana, and Ottowia were typical organic-matter-degrading bacteria that degraded chlorobenzene efficiently with xylene present.

Evaluation in the performance of the biodegradation of herbicide diuron to high concentrations by Lysinibacillus fusiformis acclimatized by sequential batch culture

We evaluated and characterized the biodegradation of the herbicide diuron in its commercial form above its saturation concentration by Lysinibacillus fusiformis acclimatized by sequential batch culturing. Acclimatization was carried out in eight cycles in liquid culture, improving the capacity of L. fusiformis to remove diuron from 55.13 ± 1.3% in the first batch to 87.2 ± 0.11% in the eighth batch. Diuron biosorption was characterized with Langmuir and Freundlich isotherms, obtaining a maximum biosorption (q_max) of 0.00885 mg mg^-1. In diuron biodegradation assays, a consumption substrate biomass yield (Y_SD/X) of 6.266 mg mg^-1 was obtained, showing that biodegradation was the main mechanism in diuron removal. Diuron biodegradation by L. fusiformis was characterized by the Monod model, with a maximum specific growth rate (μ_max) of 0.0245 h^-1 and an affinity constant (K_SD) of 344.09 mg L^-1. A low accumulation of 3,4-dichloroaniline with the production of chloride ions indicated dechlorination when diuron was present at high concentrations. A phytotoxic assay conducted with Lactuca sativa showed that the toxicity of an effluent with diuron at 250 mg L^-1 decreased when it was pretreated with acclimatized L. fusiformis. Acclimatization by sequential batch culturing improved the ability of L. fusiformis to biodegrade diuron at high concentrations, showing potential in the bioremediation of diuron-contaminated sites.

Enhanced biodegradation of chlorobenzene via combined Fe3+ and Zn2+ based on rhamnolipid solubilisation

Biotrickling filters (BTFs) for hydrophobic chlorobenzene (CB) purification are limited by mass transfer and biodegradation. The CB mass transfer rate could be improved by 150 mg/L rhamnolipids. This study evaluated the combined use of Fe³⁺ and Zn²⁺ to enhance biodegradation in a BTF over 35 day. The effects of these trace elements were analysed under different inlet concentrations (250, 600, 900, and 1200 mg/L) and empty bed residence times (EBRTs; 60, 45, and 32 sec). Batch experiments showed that the promoting effects of Fe³⁺/Zn²⁺ on microbial growth and metabolism were highest for 3 mg/L Fe³⁺ and 2 mg/L Zn²⁺, followed by 2 mg/L Zn²⁺, and lowest at 3 mg/L Fe³⁺. Compared to BTF in the absence of Fe³⁺ and Zn²⁺, the average CB elimination capacity and removal efficiency in the presence of Fe³⁺ and Zn²⁺ increased from 61.54 to 65.79 g/(m³⋅hr) and from 80.93% to 89.37%, respectively, at an EBRT of 60 sec. The average removal efficiency at EBRTs of 60, 45, and 32 sec increased by 2.89%, 5.63%, and 11.61%, respectively. The chemical composition (proteins (PN), polysaccharides (PS)) and functional groups of the biofilm were analysed at 60, 81, and 95 day. Fe³⁺ and Zn²⁺ significantly enhanced PN and PS secretion, which may have promoted CB adsorption and biodegradation. High-throughput sequencing revealed the promoting effect of Fe³⁺ and Zn²⁺ on bacterial populations. The combination of Fe³⁺ and Zn²⁺ with rhamnolipids was an efficient method for improving CB biodegradation in BTFs.

Improved degradation of n-hexane vapours using a hybrid system, a photoreactor packed with TiO2 coated-scoria granules and a multilayer biofilter

Biofiltration of hydrophobic and/or recalcitrant volatile organic compounds such as n-hexane is imperfect. In the present study, we applied a hybrid system consisting of a photoreactor packed with scoria granules coated with TiO₂ and a biofilter to improve the removal efficiency of n-hexane from the air stream. The experimental results showed that the hybrid system provided higher removal efficiencies than the single biofilter process with an inlet n-hexane concentration range of 0.11-1 g^-3 for empty bed residence times (EBRTs) of 30-120 s in the hybrid system. The removal efficiency of the single biofilter in EBRTs of 30, 60 and 120 s was 10.06%, 21.45%, and 45.98%, respectively. When the photoreactor was included as a pretreatment system (with residence time of 7-27 s) and the overall EBRTs of the system was adjusted to 30, 60 and 120 s, the removal efficiency of the hybrid system was increased to 39.79%, 63.08%, and 92.6%, respectively. The mass ratio of carbon dioxide produced as an indicator for n-hexane degradation in the hybrid system and the biofilter alone was 1.9 and 1.28, respectively. Bacterial community analysis with sequence analysis of 16S rDNA in the biofilter biomass revealed that Pseudomonas and Bacillus as predominant bacterial species were responsible for n-hexane biodegradation. Therefore, the application of the hybrid system is advantageous in enhanced n-hexane removal from the air stream.