A newly isolated and rapid denitrifier Pseudomonas citronellolis WXP-4: difference in N2O emissions under aerobic and anaerobic conditions.

A novel and efficient facultative anaerobic denitrifying bacterium was isolated and identified as Pseudomonas citronellolis WXP-4. The strain WXP-4 could achieve 100% nitrate and nitrite removal efficiency utilizing sodium succinate as a carbon source, C/N ratio 7, pH 7.0, and temperature 40 °C under both aerobic and anaerobic conditions. The bacterium could tolerate a wide range of NO3--N concentrations from 100 to 1000 mg/L with a maximum nitrogen removal rate of 32.05 mg/(L h). An interesting phenomenon was found that no N2O emission occurred during the denitrifying process under anaerobic conditions, while there was 0.06 mg/L under aerobic conditions. This phenomenon had been confirmed by fluorescence quantitative PCR and the results showed that the relative abundance of nosZ gene increased by 17-fold based on the ratio of anaerobic to aerobic, and thus, nosZ gene could encode more nitrous oxide reductase to accelerate the conversion of N2O under anaerobic conditions. Moreover, the narG, nirK, and norB genes were also identified in the denitrifying pathway of the strain WXP-4. This investigation has demonstrated enormous potential for the future application in wastewater treatment systems.

Gene cloning, expression and performance validation of nitric oxide dismutase.

Nitrous oxide (N2O) is a significant contributor to global warming and possesses an ozone-depleting impact nearly 298 times that of CO2. To reduce N2O emissions, the newly-discovered nod gene which can directly convert NO into N2 and O2 was successfully cloned from the anaerobic denitrification sludge. The recombinant plasmid containing the nod gene was built, and the expression of nod gene in Escherichia coli was determined, leading to the construction of recombinant engineering bacteria. Results showed that the recombinant engineering bacteria E. coli BL21 (DE3)-pET28a-nod could autonomously degrade NO, with a degradation rate of 72 % within 48 h, and could produce 2479.72 ppm of N2 and 75.12 mL of O2. The cumulative O2 production of the sludge sample and recombinant E. coli within 8 h was 1.75 mL and 8.45 mL, respectively. The cumulative O2 production of recombinant E. coli was at least 4.82 times higher than that of the sludge sample. The investigation proposed a new biodegradation pathway for nitrogen pollution.

Mechanisms of flame retardant tris (2-ethylhexyl) phosphate biodegradation via novel bacterial strain Ochrobactrum tritici WX3-8.

Tris (2-ethylhexyl) phosphate (TEHP) is a common organophosphorus flame retardant analog with considerable ecological toxicity. Here, novel strain Ochrobactrum tritici WX3-8 capable of degrading TEHP as the sole C source was isolated. Our results show that the strain's TEHP degradation efficiency reached 75% after 104 h under optimal conditions, i.e., 30 °C, pH 7, bacterial inoculum 3%, and

Mechanisms of N, N-dimethylacetamide-facilitated n-hexane removal in a rotating drum biofilter packed with bamboo charcoal-polyurethane composite.

n-Hexane and N, N-dimethylacetamide (DMAC) are two major volatile organic compounds (VOCs) discharged from the pharmaceutical industry. To enhance DMAC-facilitated n-hexane removal, we investigated the simultaneous removal of multiple pollutants in a rotating drum biofilter packed with bamboo charcoal-polyurethane composite. After adding 800 mg·L-1 DMAC, the n-hexane removal efficiency increased from 59.4 % to 83.1 % under the optimized conditions. The maximum elimination capacity of 10.0 g·m-3·h-1n-hexane and 157 g·m-3·h-1 DMAC were obtained. The biomass of bamboo charcoal-polyurethane and the ratio of protein-to-polysaccharide in extracellular polymeric substances were significantly increased compared with the non-DMAC stage, which is attributed to increased carbon utilization. In addition, Na+ K+-ATPase was positively correlated with increasing electron transport system activity, which was 1.98 and 1.36 times greater. Hydrophilic DMAC improved the bioavailability of hydrophobic n-hexane and benefited bacterial metabolism. Co-degradation of n-hexane and DMAC system can be used for other volatile organic pollutants.

Increasing N,N-dimethylacetamide degradation and mineralization efficiency by co-culture of Rhodococcus ruber HJM-8 and Paracoccus communis YBH-X.

In this work, Rhodococcus ruber HJM-8 and Paracoccus communis YBH-X were isolated and used to enhance N,N-dimethylacetamide (DMAC) degradation and mineralization efficiencies. The monoculture and co-culture of the two strains for DMAC degradation were compared; results indicated that, a degradation efficiency of 97.62% was obtained in co-culture, which was much higher than that of monocultures of HJM-8 (57.34%) and YBH-X (34.02%). The degradation mechanism showed that co-culture could efficiently improve extracellular polymeric substances production, electron transfer, and microbial activity. Meanwhile, the mineralization mechanism suggested that acetate was the dominant intermediate which had an inhibitory effect on HJM-8, and co-culture was conducive to mineralization due to the high performance of acetate conversion and Na+ K+-ATPase vitality. Besides, a pathway of DMAC biodegradation was proposed for co-culture: DMAC was degraded into acetate by HJM-8, then the accumulated acetate was mineralized by YBH-X. Additionally, the co-culture system was further optimized by Box-Behnken design.

Co-culturing fungus Penicillium citrinum and strain Citrobacter freundii improved nitrate removal and carbon utilization by promoting glyceride metabolism.

Exploring the interaction between denitrifying microbial species is significant for improving denitrification performance. In this study, the effects of co-culturing fungus Penicillium citrinum and strain Citrobacter freundii on denitrification were investigated. Results showed that the maximum nitrate removal and carbon utilization in co-culture were 68.0 and 14.1 mg·L-1·d-1, respectively. The total adenosine triphosphatase activity was increased to 9.87 U‧mg-1 protein in co-culture, and nicotinamide adenine dinucleotide production was 1.7-2.3 times that of monoculture, attributing to increased carbon utilization. Further metabolomics and membrane permeability assay revealed that co-culture increased the metabolism of glycerides, thereby enhancing the membrane permeability of strain Citrobacter freundii and promoting the transmembrane transport of nitrate and glucose, which boosted nitrate reductase activity and nicotinamide adenine dinucleotide production in turn. In summary, co-culturing promoted carbon utilization and enhanced substrate removal efficiency through the metabolism of glycerides, which provided a strategy to enhance denitrification performance in wastewater treatment.

Bamboo charcoal powder-based polyurethane as packing material in biotrickling filter for simultaneous removal of n-hexane and dichloromethane.

Bamboo charcoal powder-based polyurethane (BC-PU) was firstly applied in biotrickling filter to treat n-hexane and dichloromethane (DCM) simultaneously. Maximum elimination capacity of 12.68 g m-3h-1 n-hexane was achieved and exceed 30.28 g m-3h-1 DCM could be degraded. BTF respond quickly to the mixed shock loadings, and recovered to 76% and 100% respectively in less than 1 h. By increasing inlet loading (IL) of DCM from 6.20 g m-3h-1 to 28.36 g m-3h-1, the removal efficiency of n-hexane decreased from 73.4% to 55.9% corresponding to the IL of 19.96 g m-3h-1. N-hexane degradation was inhibited by high IL of DCM due to enzymes competition for active sites. The growth of key microorganisms Mycobacterium sp., Hyphomicrobium sp. was stimulated and colonized. BC-PU is an innovative and applicable bio-based material in the process of biological purification, which could be widely applied to treat hydrophobic pollutants in the pharmaceutical industry.

Enhanced adsorption and reduction performance of nitrate by Fe-Pd-Fe3O4 embedded multi-walled carbon nanotubes.

Multi walled carbon nanotubes (MWCNTs) have attracted more and more attention as adsorbents due to their excellent adsorption properties. By loading metal particles on MWCNTs, the chemical reduction ability of adsorbed pollutants could be provided, so as to achieve the purpose of adsorption and degradation of pollutants. Therefore, the removal process of NO3--N by Fe-Pd-Fe3O4/MWCNTs was studied, including rapid adsorption of initial pollutants, gradual reduction of intermediate products and re-adsorption of final products. The results showed that Fe-Pd-Fe3O4/MWCNTs completely removed NO3--N within 2 h, 39% and 25% of which were converted into NO2--N and NH4+-N. The adsorption efficiency, kinetics, capacity and adsorption energy all followed the order of NH4+-N > NO2--N > NO3--N. With the recoverability and reusability of Fe-Pd-Fe3O4/MWCNTs having been confirmed in 5 consecutive cycles, the removal rate of NO3--N still reached 43%. It has been shown that MWCNTs prolonged the reducing power for NO3--N, due to avoiding the aggregation of metal particles. The rapid adsorption of initial pollutants, effective stepwise reduction and convenient recovery processes were of great value for the rehabilitation of polluted water.

Efficient biotransformation of sulfide in anaerobic sequencing batch reactor by composite microbial agent: performance optimization and microbial community analysis.

Sulfur-containing wastewater is very common as an industrial waste, yet a high-efficiency composite microbial agent for sulfur-containing wastewater treatment is still lacking. In this work, three novel and efficient desulfurizing bacteria were isolated from the sewage treatment tank of Zhejiang Satellite Energy Co., Ltd. They were identified as Brucella melitensis (S1), Ochrobactrum oryzae (S8), and Achromobacter xylosoxidans (S9). These three strains of bacteria were responsible for the oxidative metabolism of sodium sulfide via a similar polythionate pathway, which could be expressed as follows: S2-→S2O32-/S0→SO32-→SO42-. Activated carbon, wheat bran, and diatomite at 1:1:1 ratio are used as carriers to construct a composite microbial agent containing the three bacteria. The desulfurization efficiency of 95% was predicted by response surface methodology under the following optimum conditions: the dosage of the inoculum was 3 g/L, pH 7.86, and temperature of 39 °C. Additionally, the impact resistance was studied in the anaerobic sequencing batch reactor. The removal capacity of microbial agent reached 98%. High-throughput analysis showed that composite microbial agent increased bacterial evenness and diversity, and the relative abundance of Brucellaceae increased from 5.04 to 8.79% in the reactor. In the process of industrial wastewater transformation, the transformation rate of sulfide by composite microbial agent was maintained between 70 and 81%. The composite microbial agent had potential for the treatment of sulfur-containing wastewater.

Improvement of Alcaligenes sp.TB performance by Fe-Pd/multi-walled carbon nanotubes: Enriched denitrification pathways and accelerated electron transport.

Aiming at the accumulation of NO2--N and N2O during denitrification process, this work focused to improve the denitrification performance by Pd-Fe embedded multi-walled carbon nanotubes (MWCNTs). The main conclusions were as follows: 30 mg/L Pd-Fe/MWCNTs have shown an excellent promotion on denitrification (completely TN removal at 36 h). Meanwhile, enzyme activity results indicated that the generation of NO2--N, NH4+-N by Pd-Fe/MWCNTs led the occur of short-cut denitrification by increasing 203.9% the nitrite reductase activity. Furthermore, electrochemical results and index correlation analysis confirmed that the electron exchange capacity (1.401 mmol eg-1) of Pd-Fe/MWCNTs was positively related to nitrite reductase activity, indicating its crucial role in electron transport activity (0.46 µg O2/(protein·min) at 24 h) during denitrification process by Pd-Fe/MWCNTs played a role of chemical reductant and redox mediator.

Reduction of FeII(EDTA)-NO by Mn powder in wet flue gas denitrification technology: stoichiometry, kinetics, and thermodynamics.

Conversion of FeII(EDTA)-NO or FeIII(EDTA) into FeII(EDTA) is a key process in a wet flue gas denitrification technology with FeII(EDTA) solution. In this work, the stoichiometry, kinetics, and thermodynamics of FeII(EDTA)-NO reduction by Mn powder were investigated. We first studied the FeII(EDTA)-NO reduction and product distribution to speculate a possible stoichiometry of FeII(EDTA)-NO reduction by Mn powder. Then, the effects of major influencing factors, such as pH value, temperature, and Mn concentration, were studied. The pseudo-second-order model was established to describe the FeII(EDTA)-NO reduction. Simultaneously, according to Arrhenius and Eyring-Polanyi equations, the reaction activation energy (Ea), enthalpy of activation (∆H‡), and entropy of activation (∆S‡) were calculated as 23.68 kJ/mol, 21.148 kJ/mol, and - 149.728 J/(k mol), respectively. Additionally, simultaneous reduction of FeIII(EDTA) and FeII(EDTA)-NO was investigated to better study the mechanism of FeII(EDTA) regeneration, suggesting that there was a competition between the two reduction processes. Finally, a simple schematic mechanism of NO absorption by FeII(EDTA) combined with regeneration of manganese ion and ammonium was proposed. These fundamental researches could offer a valuable guidance for wet flue gas denitrification technology with FeII(EDTA) solution.