Enhancing biological conversion of NO to N2O by utilizing thermophiles instead of mesophiles.

The production of nitrous oxide (N2O) through the biological denitrification of nitric oxide (NO) from flue gases has recently been achieved. Although the temperature of flue gas after desulphurization is usually 45-70 °C, all previous studies conducted microbial denitrification of NO under mesophilic conditions (22-35 °C). This study investigated the biological conversion of NO to N2O in both mesophilic (35-45 °C) and thermophilic conditions (45-50 °C). The results showed that temperature has a great impact on N2O production, with a maximum conversion efficiency (from NO to N2O) of 82% achieved at 45 °C, which is obviously higher than the reported conversion efficiencies (24-71%) under mesophilic conditions. Additionally, high-throughput sequencing result showed that the genera Enterococcus, Clostridium, Romboutsia, and Streptococcus were closely related to NO denitrification and N2O production. Microbial communities at 40 and 45 °C had greater metabolizing capacities for polymeric carbon sources. This study suggests that thermophilic condition (45 °C) is more suitable for biological production of N2O from NO.

Effect of weak electrical stimulation on m-dichlorobenzene biodegradation in biotrickling filters: Insights from performance and microbial community analysis.

The microbial electrolysis cell coupled with the biotrickling filters (MEC-BTF) was developed for enhancing the biodegradation of gaseous m-dichlorobenzene (m-DCB) through weak electrical stimulation. The maximum removal efficiency and elimination capacity in MEC-BTF were 1.48 and 1.65 times higher than those in open-circuit BTF (OC-BTF), respectively. Weak electrical stimulation had a positive impact on the characteristics of the biofilm. Additionally, microbial community analysis revealed that weak electrical stimulation increased the abundance of key functional genera (e.g., Rhodanobacter and Bacillus) and genes (e.g., catA/E and E1.3.1.32), thereby accelerating reductive dechlorination and ring-opening of m-DCB. Macrogenomic sequencing further revealed that electron transfer pathway in MEC-BTF might be mediated through extracellular electroactive mediators and cytochromes.

Quorum sensing improved the low-temperature performance of biofilters treating gaseous toluene.

Biofilters usually have poor VOC removal performance at temperatures lower than 20 °C. In this study, two quorum sensing (QS) enhancement methods, which are addition of exogenous N-acyl-homoserine lactones (AHLs) and inoculation of AHL-producing bacteria, were applied in biofilters treating gaseous toluene at a low temperature of 12 °C. Their effects on biofilter performance and biofilm characteristics were investigated. The results showed that adding exogenous AHLs and AHL-producing bacteria in biofilters raised the average toluene elimination capacity by 39% and 26% respectively, and raised the average mineralization efficiency by 25% and 47% respectively in first 24 days. In addition, the two QS enhancement methods could increase the attached biomass by 48% and 87% respectively and made the biofilm distribute more uniform by increasing its extracellular polymeric substances content and microbial adhesive strength. The two QS enhancement methods resulted in more mesopores in biofilm, lower O/C and (O+N)/C of organic elements in biofilm, and increased the solubility of toluene in liquid phase, which all benefit VOCs mass transfer in biofilters. These results demonstrate that QS enhancement methods have the potential to optimize the biofilm and thus improve the performance of biofilters treating VOCs at a low temperature. This work provides us a new choice to improve industrial-scale biofilters treating VOCs at high latitude regions or in winter.

Two quorum sensing enhancement methods optimized the biofilm of biofilters treating gaseous chlorobenzene.

In this study, effects of two quorum sensing (QS) enhancement methods on the performance and biofilm of biofilters treating chlorobenzene were investigated. Three biofilters were set up with BF1 as a control, BF2 added exogenous N-acyl-homoserine lactones (AHLs) and BF3 inoculated AHLs-producing bacterium identified as Acinetobacter. The average chlorobenzene elimination capacities were 73 and 77 g/m3/h for BF2 and BF3 respectively, which were significantly higher than 50 g/m3/h for BF1. The wet biomass of BF2 and BF3 with QS enhancement eventually increased to 60 and 39 kg/m3 respectively, and it was 29 kg/m3 for BF1. Analysis on biofilms in three biofilters showed that distribution uniformity, extracellular polymeric substances production, adhesive strengths, viability, and metabolic capacity of biofilms were all prompted by the two QS enhancement methods. Comparisons between the two QS enhancement methods showed that adding exogenous AHLs had more significant enhancing effect on biofilm due to its higher AHLs level in start-up period, while AHLs-producing bacteria had an advantage in enhancing bacterial community diversity. These results demonstrate that QS enhancement methods have the potential to optimize the biofilm and thus improve the performance of biofilters treating recalcitrant VOCs.

Sustaining low pressure drop and homogeneous flow by adopting a fluidized bed biofilter treating gaseous toluene.

A biofilter treating gaseous VOCs is usually a packed bed system which will encounter bed clogging problems with increased pressure drop and uneven gas flow in the filter bed. In this study, a lab-scale fluidized bed reactor (FBR) was set up treating gaseous toluene and compared with a packed bed reactor (PBR) with the same bed height of 150 cm. During 45 days of operation, the average elimination capacity of the FBR was 242 g m-3∙h-1, similar to that in the PBR (228 g m-3∙h-1) under an inlet toluene concentration of 100-300 mg m-3 and an empty bed residence time (EBRT) of 0.60 s. A better mass transfer was also confirmed in the FBR by molecular residence time distribution measurement. The pressure drop of the PBR increased dramatically and exceeded 8000 Pa m-1 while that of the FBR maintained approximately 200 Pa m-1. On the 40th day, the air flow distribution in the FBR was more homogeneous than that in the PBR. The differences in pressure drop and air flow distribution were due to a much lower and more uniform distribution of biomass in the FBR than that in the PBR. The detached biomass collected from the off-gas of the FBR was almost 13 times of that from the PBR. Similar microbial community structures were observed in both systems, with the dominant bacterial genus Stenotrophomonas and the fungal genera Meyerozyma, Aspergillus. The results in this study demonstrated that the FBR could achieve a more stable performance than a PBR in long-term operation.

Enhancing biofilm formation in biofilters for benzene, toluene, ethylbenzene, and xylene removal by modifying the packing material surface.

Polyurethane (PU) sponges are popular packing material in biofilters and their smooth and hydrophobic surface often leads to an uneven distribution and detachment of biofilms. In this work, the surface of PU sponge was modified to obtain higher roughness and positive charge. The performances of two biofilters (BF1 with pristine sponge and BF2 with modified sponge) for benzene, toluene, ethylbenzene, and xylene (BTEX) removal were investigated. Total Volatile Organic Compound (TVOC) removal efficiency and CO2 increment were 61% and 804 ppm for BF2 respectively after start-up, compared with 51% and 538 ppm for BF1. Analysis on biofilms showed that the modification of PU sponge significantly improved the microbial growth, viability and adhesive strength in biofilms, reduced extracellular polymeric substance (EPS) and changed the microbial community. These results demonstrate that modified sponge can enhance biofilm formation and BTEX removal in biofilters and may applied in large-scale applications.

Screening and characterization of mixotrophic sulfide oxidizing bacteria for odorous surface water bioremediation.

Eight species of mixotrophic sulfide oxidizing bacteria (SOB) were isolated from activated sludge and identified using 16S rRNA sequence analysis. The effects of organic substances, dissolved oxygen (DO) and nitrate on sulfide oxidation and bacterial growth were studied in this work. The results showed that Paracoccus sp. (N1), Pseudomonas sp. (N2) and Pseudomonas sp. (S4) have strong adaptability to environments with low DO and high concentrations of organic substance. An SOB additive was optimized in artificial, odorous water. The optimized SOB additive is ablendof 80% N1 and 20% N2 bacteria solution with absorbance equal to 0.5 at a wavelength of 600 nm (OD600), and the optimal dose of the additive is 20 ml/L. Oxidation-reduction potential (ORP), ammonia-nitrogen (NH3-N) and released H2S in an odorous river were measured with and without SOB additive, and the results indicated that the optimized SOB additive has excellent performance for odorous river bioremediation.

Enhanced removal of gaseous 1,3-dichlorobenzene in biotrickling filters by rhamnolipid and Mg (II).

In this study, the effect of rhamnolipid and Mg (II) on microbial growth and 1,3-dichlorobenzene removal was investigated in two identical lab-scale biotrickling filters (named BTF1 and BTF2). The contact angle and Henry's constant were detected at various concentrations of rhamnolipid and the results indicated that rhamnolipid is able to effectively improve the solubility of 1,3-dichlorobenzene in medium. The results of the experiments in BTFs showed that the optimal concentrations of rhamnolipid and Mg (II) were 170 mg/L and 2 mg/L, respectively. The removal efficiency (RE) of 1,3-dichlorobenzene decreased from 100% to 57.13% for BTF1 that was not fed with rhamnolipid and Mg (II) and from 100% to 86.26% for BTF2 that was fed with rhamnolipid and Mg (II) when the inlet loading rate increased from 2.87 to 83.83 g/(m3 h) at an empty bed residence time (EBRT) of 60 s. The dissolved oxygen (DO) was analyzed throughout the entire period and the results showed that the two additives can significantly promote oxygen transfer. In addition, the microbial adhesive strength and community were observed and compared to show the positive role of rhamnolipid and Mg (II).

Biotoxicity of Water-Soluble UV Photodegradation Products for 10 Typical Gaseous VOCs.

Ultraviolet (UV) photodegradation is increasingly applied to control volatile organic compounds (VOCs) due to its degradation capabilities for recalcitrant compounds. However, sometimes the UV photodegradation products are also toxic and can affect human health. Here, 10 VOCs at 150~200 ppm in air were treated using a laboratory-scale UV reactor with 185/254 nm irradiation, and the biotoxicity of their off-gas was studied by investigating their off-gas absorption solutions. The CO2 increase and VOC decrease were 39~128 ppm and 0~42 ppm, respectively, indicating that the VOCs and their products were mineralized in off-gas absorption solutions. The total organic carbon (TOC) of the absorption solutions are 4~20 mg∙L-1. Luminescent bacteria and Daphnia magna were used to detect the acute toxicity, and an umu assay was used to determine the genotoxic potential. Trichloroethylene showed a highest toxicity to luminescent bacteria, while chlorobenzene had the lowest toxicity. Water-soluble UV photodegradation products for styrene are very toxic to Daphnia magna. In the umu assay, the genotoxicities of off-gas absorption solutions of trichloroethylene, methylbenzene, ethyl acetate, butyl alcohol, and styrene were 51.26, 77.80, 86.89, 97.20, and 273.62 mg (4-NQO)·L-1 respectively. In addition, the analysis of the genotoxicity/TOC and intermediates products indicated that the off-gas absorption solutions of styrene, trichloroethylene, and butyl alcohol contain many highly toxic substances.

Kinetic analysis and degradation pathway for m-dichlorobenzene removal by Brevibacillus agri DH-1 and its performance in a biotrickling filter.

A strain, Brevibacillus agri DH-1, isolated from dry lands was used to remove m-dichlorobenzene. After 48h culturing, the concentrations of m-dichlorobenzene decreased from 26-130 to 7.87-28.87mg/L and dry cell weight for bacterial growth reached 52.43-75.05mg/L. The growth and degradation kinetics were analyzed by the fitting of Haldane-Andrews model and pseudo first-order model. A degradation pathway was proposed according to major intermediates (phenol), chloride ion variation, ring-opening enzyme activity, and high mineralization (0.47gCl-/gm-dichlorobenzene, 0.65 gco2/gm-dichlorobenzene, 0.15 gDCW/gm-dichlorobenzene). In addition, the performance in a biotrickling filter (BTF) was evaluated through removal efficiency and pressure drop values with increasing inlet loading rate from 4.10 to 122.57g/m3/h at three empty bed residence time points (30s, 60s, and 90s). The results demonstrated that strain DH-1 possessed high removal efficiency and stable operation in a BTF.