Sujing Li

Degradation pathway and kinetic analysis for p-xylene removal by a novel Pandoraea sp. strain WL1 and its application in a biotrickling filter

In this study, a novel Pandoraea sp. strain WL1 capable of mineralizing p-xylene as sole carbon and energy source was isolated from the activated sludge of a pharmaceutical wastewater treatment plant. A nearly complete degradation of 16.6∼99.4 mg L(-1)p-xylene in the liquid-phase was achieved within 6∼18 h accompanied by 15.9∼56.3 mg dry cell weight (DCW)L(-1) for bacterial growth. A complete pathway for p-xylene degradation by strain WL1 was presented through identification of a major intermediate (p-toluic acid) and final products (2.193 gCO2 gp-xylene(-1) of CO₂ production and 0.215 g DCW gp-xylene(-1) of bacterial yield). Kinetics of bacterial growth and p-xylene degradation were evaluated using Haldane-Andrews model and pseudo first-order model, respectively. Furthermore, a biotrickling filter (BTF) was employed to evaluate the application of strain WL1 on the removal of gas-phase p-xylene under gas flow rates of 0.41∼1.98 m(3)h(-1) for inlet loading rates of 5∼248 gm(-3)h(-1). The BTF inoculated with strain WL1 proved to be robust against fluctuations of gas flow rates and inlet p-xylene concentrations. All the results obtained highlight the potential of strain WL1 for the treatment of p-xylene.

Phosphorus removal of rural wastewater by the paddy-rice-wetland system in Tai Lake Basin.

A field experiment was conducted to remove the potential eutrophication effect of P from rural wastewater (RW) during the whole rice growing season of 2007. The experiments consisted of five treatments, namely black water (BW), domestic wastewater (DW), grey water (GW), surface lake water (SW) and surface lake water without P application as a check (CK), with three replicates in a randomized block design. Commercial fertilizer and RW were applied to furnish 40 kg Pha(-1) except CK. Results showed total P (TP) concentration had significantly declined after P application, from October 15 there were no significant increases in TP concentration in the floodwater. TP removal rates from RW was significantly higher (P<or=0.05) than those from fertilizer. TP load was in an overall gradual decline, whereupon it became approximately steady on October 1. The percentage of TP load from wastewater decreased, whereas that from fertilizer continued to increase. Meanwhile, the yield for CK was significantly less (P<or=0.05) than SW, GW, DW, and BW, with the yield of BW significantly greater (P<or=0.05) than other treatments. It is feasible to remove P from RW by the paddy-rice-wetland system and can be widely used to improve the yield of rice.

Life cycle assessment on biogas production from straw and its sensitivity analysis

This study aims to investigate the synthetically environmental impacts and Global Warming Potentials (GWPs) of straw-based biogas production process via cradle-to-gate life cycle assessment (LCA) technique. Eco-indicator 99 (H) and IPCC 2007 GWP with three time horizons are utilized. The results indicate that the biogas production process shows beneficial effect on synthetic environment and is harmful to GWPs. Its harmful effects on GWPs are strengthened with time. Usage of gas-fired power which burns the self-produced natural gas (NG) can create a more sustainable process. Moreover, sensitivity analysis indicated that total electricity consumption and CO2 absorbents in purification unit have the largest sensitivity to the environment. Hence, more efforts should be made on more efficient use of electricity and wiser selection of CO2 absorbent.

Inhibitory effect of SO2 on side reactions of NH3-SCR over olivine

Olivine catalysts prepared by calcination achieved high N2 selectivity and good NH3-SCR activity at 150–450 °C. The existence of SO2 significantly inhibited the formation of NO and N2O in the NH3-SCR reaction at the temperature range of 325–450 °C. This is mainly because of the reductive properties of SO2 that could restrain the over-oxidization of NH3. Therefore, both the NOx conversion and N2 selectivity were improved at high temperatures. Accordingly, the presence of SO2 shifted the optimal temperature window of the olivine catalyst by about 75 °C towards high temperature. Both the Langmuir–Hinshelwood mechanism and the Eley–Rideal mechanism contributed to the SCR reaction over the olivine catalyst. Temperature-programmed desorption experiments show that excess ammonium sulfate formed in the presence of SO2 suppressed the reaction of adsorbed NOx species with adsorbed NH3 species at low temperatures. Lots of activated NH3 species (−NH2) were formed by the decomposition of ammonium sulfate at high temperatures, promoting the reaction of adsorbed NH3 species (−NH2) with both adsorbed NOx and gaseous NOx. Preliminary results suggest that olivine is a potential catalyst for treating sulfur-containing exhausts.

A Biophysicochemical Model for NO Removal by the Chemical Absorption–Biological Reduction Integrated Process

The chemical absorption-biological reduction (CABR) integrated process is regarded as a promising technology for NOx removal from flue gas. To advance the scale-up of the CABR process, a mathematic model based on mass transfer with reaction in the gas, liquid, and biofilm was developed to simulate and predict the NOx removal by the CABR system in a biotrickling filter. The developed model was validated by the experimental results and subsequently was used to predict the system performance under different operating conditions, such as NO and O2 concentration and gas and liquid flow rate. NO distribution in the gas phase along the biotrickling filter was also modeled and predicted. On the basis of the modeling results, the liquid flow rate and total iron concentration were optimized to achieve >90% NO removal efficiency. Furthermore, sensitivity analysis of the model revealed that the performance of the CABR process was controlled by the bioreduction activity of Fe(III)EDTA. This work will provide the guideline for the design and operation of the CABR process in the industrial application.

Bioelectrochemical Reduction of Fe(II)EDTA–NO in a Biofilm Electrode Reactor: Performance, Mechanism, and Kinetics

A biofilm electrode reactor (BER) is proposed to effectively regenerate Fe(II)EDTA, a solvent for NOx removal from flue gas, from Fe(II)EDTA-NO, a spent solution. In this study, the performance, mechanism, and kinetics of the bioelectrochemical reduction of Fe(II)EDTA-NO were investigated. The pathways of Fe(II)EDTA-NO reduction were investigated via determination of nitrogen element balance in the BER and an abiotic electrode reactor. The experimental results indicate that the chelated NO (Fe(II)EDTA-NO) is reduced to N2 with N2O as an intermediate. However, the oxidation of NO occurred in the absence of Fe(II)EDTA in abiotic reactors. Furthermore, the accumulation of N2O was suppressed with the help of electricity. The preponderant electron donor for reduction of Fe(II)EDTA-NO was also confirmed via analysis of the electron conservation. About 87% of Fe(II)EDTA-NO was reduced using Fe(II)EDTA as the electron donor in the presence of both glucose and cathode electrons while the cathode electrons were utilized for the reduction of Fe(III)EDTA to Fe(II)EDTA. Michaelis-Menten kinetic constants of bioelectrochemical reduction of Fe(II)EDTA-NO were also calculated. The maximum reduction rate of Fe(II)EDTA-NO was 13.04 mol m(-3) h(-1), which is 50% higher than that in a conventional biofilter.

Pathway of FeEDTA transformation and its impact on performance of NOx removal in a chemical absorption-biological reduction integrated process

A novel chemical absorption-biological reduction (CABR) integrated process, employing ferrous ethylenediaminetetraacetate (Fe(II)EDTA) as a solvent, is deemed as a potential option for NOx removal from the flue gas. Previous work showed that the Fe(II)EDTA concentration was critical for the NOx removal in the CABR process. In this work, the pathway of FeEDTA (Fe(III)/Fe(II)-EDTA) transformation was investigated to assess its impact on the NOx removal in a biofilter. Experimental results revealed that the FeEDTA transformation involved iron precipitation and EDTA degradation. X-ray photoelectron spectroscopy analysis confirmed the iron was precipitated in the form of Fe(OH)3. The iron mass balance analysis showed 44.2% of the added iron was precipitated. The EDTA degradation facilitated the iron precipitation. Besides chemical oxidation, EDTA biodegradation occurred in the biofilter. The addition of extra EDTA helped recover the iron from the precipitation. The transformation of FeEDTA did not retard the NO removal. In addition, EDTA rather than the iron concentration determined the NO removal efficiency.

Generation, Utilization, and Transformation of Cathode Electrons for Bioreduction of Fe(III)EDTA in a Biofilm Electrode Reactor Related to NOx Removal from Flue Gas

A chemical absorption-biological reduction (CABR) integrated system, which employs iron chelate as a solvent, is under development for NOx removal from flue gas. Biofilm electrode reactor (BER) is deemed as a promising bioreactor to regenerate the iron chelate. Although it has been proved that BER can significantly enhance the bioreduction of Fe(III)EDTA, the bioelectrochemistry mechanism involved in the bioreduction of Fe(III)EDTA remains unknown. This work aims to explore this mechanism via the analysis of the generation, utilization, and transformation of cathode electrons in the BER. The results indicate that the generation of cathode electrons follows Faradays law. The generated cathode electrons were used to produce H2 and directly reduce Fe(III)EDTA in the BER. Meanwhile, the produced H2 served as an electron donor for bioreduction of Fe(III)EDTA. The excess H2 product was transformed to simple organics, e.g., methanol by the hydrogen autotrophy of Pseudomonas under the inorganic and anaerobic conditions. Overall, this work revealed that the reduction of Fe(III)EDTA in the BER was enhanced by both direct electrochemical reduction and indirect bioreduction using H2 as an intermediate. It is also interesting that the excess H2 product was transformed to methanol for microbial metabolism and energy storage in the BER.

o-Xylene removal using one- and two-phase partitioning biotrickling filters: steady/transient-state performance and microbial community

ABSTRACT In this study, one- and two-phase partitioning biotrickling filters (1P-BTF and 2P-BTF, respectively) inoculated with a pre-acclimated mixed culture were examined for the removal of hydrophobic and refractory o-xylene. A small fraction of silicone oil (5% v/v) was added as a non-aqueous phase. Due to the presence of silicone oil, the 2P-BTF exhibited superior performance and stability for o-xylene biodegradation at steady and transient operations. Higher macro-kinetic constants for o-xylene removal by the Michaelis–Menten model were obtained for the 2P-BTF with a saturation constant of 0.396 g m−3 and a maximum elimination capacity of 105.7 g m−3 h−1. The enhancement of removal performance for the 2P-BTF was supported by dominant specialized microorganisms with o-xylene biodegradability. The diversity of microbial community was influenced by the presence of silicone oil. This study demonstrated that a BTF with 5% of silicone oil could be applied for the treatment of hydrophobic and refractory volatile organic compounds. It also provided valuable information for better understanding the relationship between microbial community and removal performance using two-phase partitioning bioreactors.

Electron transfer mechanism of biocathode in a bioelectrochemical system coupled with chemical absorption for NO removal

A biocathode with the function of Fe(III)EDTA and Fe(II)EDTA-NO reduction was applied in a microbial electrolysis cell coupled with chemical absorption for NO removal from flue gas. As the mediated electron transfer was excluded by the same electrochemical characterizations of the biocathodes before and after a 48 h continuous operation, the profiles of reduction experiments indicated that direct electron transfer was the main mechanism of Fe(III)EDTA reduction, while Fe(III)EDTA-NO was mainly reduced via Fe(II)-assisted autotrophic denitrification. The microscopy of the biocathode confirmed the existence of pili, which was supposed to be bacterial nanowires for electron transfer. The analysis of microbial community revealed that iron-reducing bacteria, including Escherichia coli, had the possibility of electron uptake from electrode via physical contact. These results first time gave us in-depth understanding of the electron transfer in the multifunctional biocathode and mechanism for further enhancement of the bioreduction processes.