Simultaneous biodegradation of volatile and toxic contaminant mixtures by solid-liquid two-phase partitioning bioreactors

Multi-factorial analysis of the removal of dichloromethane and toluene in an airlift packing bioreactor

Biotechnology has proven effective in removing a wide variety of VOCs. In this study, the effects of pH (from 3 to 7), operating temperature (20-30 °C), empty bed residence time (EBRT, 10-40 s) and transient inlet concentration (400-4000 mg m^-3) on the removal performance of an airlift packing bioreactor (ALPR) was investigated. The removal efficiency (RE) and stability of the ALPR was evaluated and compared with the conventional airlift bioreactor (ALR). The results showed that under the influence of single factor variation, the ALPR showed significant higher RE and better stability than the ALR in removing dichloromethane (DCM) and toluene. Besides, a factorial design was used to analyses the interaction of multiple factors and their influence on the removal of DCM and toluene in the ALPR and ALR. It shows that pH value has the most significant influence, and plays a crucial role in maintaining high RE of DCM and toluene in both of the ALPR and ALR. Temperature has a great effect on the removal of toluene. EBRT has certain effect on the removal of DCM in the ALPR. The transient concentration of a single substrate has a significant negative effect on the RE of this substrate, while it does not significantly affect the removal of another substrate in the ALPR. However, the steep increase of DCM concentration has an adverse effect on the RE of high concentration toluene in the ALR. The overall RE and degradation capacity of both toluene and DCM by the ALPR are much higher than that of the conventional ALR.

The biological treatment of synthetic fracking fluid in an extractive membrane bioreactor: Selective transport and biodegradation of hydrophobic and hydrophilic contaminants

The biodegradation of selected organic constituents present in hydraulic fracturing wastewater were examined in an extractive membrane bioreactor (EMB) operating with Hytrel™ 3548 tubing. Synthetic hydraulic fracturing wastewater was generated via an extensive literature review and contained high concentrations (1000 mg L^-1) of contaminant compounds of varied hydrophobicity, viz. methyl ethyl ketone, benzene, phenol and acetic acid, as well as 30-120 g L^-1 of Cl^- at low pH. This hostile wastewater was circulated through the polymeric tubing, selectively transporting the organic compounds through the membrane for biological degradation by an enriched bacterial consortium. 16S rDNA analysis revealed the presence of five dominant microbial strains within the consortium, including: Pseudomonas sp., Comamonas sp., Achromobacter sp., Lysinibacillus sp., and Oxalobacter sp. EMBs in batch operation achieved 99% removal of methyl ethyl ketone, benzene, and phenol after 72 h and effectively removed acetic acid up to its ionization point. Continuous EMB operation provided 99% removal of benzene and phenol, 96% removal of methyl ethyl ketone, and 53% of acetic acid. The treatment of synthetic hydraulic fracturing fluid demonstrated the effectiveness of carefully selected amphiphilic polymers in EMBs for treating the hydrophilic and hydrophobic organic profile found in hydraulic fracturing wastewaters.

Quantitative structure-activity relationship for the partition coefficient of hydrophobic compounds between silicone oil and air

The silicon oil-air partition coefficients (K_SiO/A) of hydrophobic compounds are vital parameters for applying silicone oil as non-aqueous-phase liquid in partitioning bioreactors. Due to the limited number of K_SiO/A values determined by experiment for hydrophobic compounds, there is an urgent need to model the K_SiO/A values for unknown chemicals. In the present study, we developed a universal quantitative structure-activity relationship (QSAR) model using a sequential approach with macro-constitutional and micromolecular descriptors for silicone oil-air partition coefficients (K_SiO/A) of hydrophobic compounds with large structural variance. The geometry optimization and vibrational frequencies of each chemical were calculated using the hybrid density functional theory at the B3LYP/6-311G** level. Several quantum chemical parameters that reflect various intermolecular interactions as well as hydrophobicity were selected to develop QSAR model. The result indicates that a regression model derived from logK_SiO/A, the number of non-hydrogen atoms (#nonHatoms) and energy gap of E_LUMO and E_HOMO (E_LUMO-E_HOMO) could explain the partitioning mechanism of hydrophobic compounds between silicone oil and air. The correlation coefficient R² of the model is 0.922, and the internal and external validation coefficient, Q²_LOO and Q²_ext , are 0.91 and 0.89 respectively, implying that the model has satisfactory goodness-of-fit, robustness, and predictive ability and thus provides a robust predictive tool to estimate the logK_SiO/A values for chemicals in application domain. The applicability domain of the model was visualized by the Williams plot.

Regeneration strategies of polymers employed in ex-situ remediation of contaminated soil: Bioregeneration versus solvent extraction

In this study we evaluated the feasibility of two regeneration strategies of contaminated polymers employed for ex-situ soil remediation in a two-step process. Soil decontamination is achieved by sorption of the pollutants on the polymer beads, which are regenerated in a subsequent step. Tested soil was contaminated with a mixture of 4-chlorophenol and pentachlorophenol, and a commercial polymer, Hytrel, has been employed for extraction. Removal efficiencies of the polymer-soil extraction are in the range of 51-97% for a contact time ≤ 24 h. Two polymer regeneration strategies, solvent extraction and biological regeneration (realized in a two-phase partitioning bioreactor), were tested and compared. Performance was assessed in terms of removal rates and efficiencies and an economic analysis based on the operating costs has been performed. Results demonstrated the feasibility of both regeneration strategies, but the bioregeneration was advantageous in that provided the biodegradation of the contaminants desorbed from the polymer. Practically complete removal for 4-chlorophenol and up to 85% biodegradation efficiency for pentachlorophenol were achieved. Instead, in the solvent extraction, a relevant production (184-831 L kg(pol)(-1)) of a highly polluted stream to be treated or disposed of is observed. The cost analysis of the two strategies showed that the bioregeneration is much more convenient with operating costs of ∼12 €/kg(pol) i.e. more than one order of magnitude lower in comparison to ∼233 €/kg(pol) of the solvent extraction.

Biodegradation of toluene in a two-phase partitioning bioreactor--impact of activated sludge acclimation

A two-phase partitioning bioreactor was considered to remove toluene contained in a biodegradable organic phase by activated sludge (AS). The selected solvent was hexadecane. In a first step, the biodegradation of toluene dissolved in hexadecane by AS was examined. In a second step, acclimation of the AS was carried out in order to improve the biodegradation rate. Acclimation improved toluene removal, since biodegradation yield increased from 72% to more than 91%. A total consumption was observed after only 4 days culture with acclimated AS, since the rest of the toluene corresponded to gas leak; while in the case of non-acclimated sludge, losses cannot account for all non-degraded toluene. Regarding hexadecane, acclimation also improved its degradation, from 43% to 79% after 6 days culture for non-acclimated and acclimated AS, respectively.