Xiaoyu Yong

Effect of NaX zeolite-modified graphite felts on hexavalent chromium removal in biocathode microbial fuel cells

Two kinds of NaX zeolite-modified graphite felts were used as biocathode electrodes in hexavalent chromium (Cr(VI))-reducing microbial fuel cells (MFCs). The one was fabricated through direct modification, and the other one processed by HNO3 pretreatment of graphite felt before modification. The results showed that two NaX zeolite-modified graphite felts are excellent bio-electrode materials for MFCs, and that a large NaX loading mass, obtained by HNO3 pretreatment (the HNO3-NaX electrode), leads to a superior performance. The HNO3-NaX electrode significantly improved the electricity generation and Cr(VI) removal of the MFC. The maximum Cr(VI) removal rate increased to 10.39±0.28 mg/L h, which was 8.2 times higher than that of the unmodified control. The improvement was ascribed to the strong affinity that NaX zeolite particles, present in large number on the graphite felt, have for microorganisms and Cr(VI) ions.

Bio-Electron-Fenton (BEF) process driven by microbial fuel cells for triphenyltin chloride (TPTC) degradation

The intensive use of triphenyltin chloride (TPTC) has caused serious environmental pollution. In this study, an effective method for TPTC degradation was proposed based on the Bio-Electron-Fenton process in microbial fuel cells (MFCs). The maximum voltage of the MFC with graphite felt as electrode was 278.47% higher than that of carbon cloth. The electricity generated by MFC can be used for in situ generation of H2O2 to a maximum of 135.96μmolL-1 at the Fe@Fe2O3(*)/graphite felt composite cathode, which further reacted with leached Fe2+ to produce hydroxyl radicals. While 100μmolL-1 TPTC was added to the cathodic chamber, the degradation efficiency of TPTC reached 78.32±2.07%, with a rate of 0.775±0.021μmolL-1h-1. This Bio-Electron-Fenton driving TPTC degradation might involve in SnC bonds breaking and the main process is probably a stepwise dephenylation until the formation of inorganic tin and CO2. This study provides an energy saving and efficient approach for TPTC degradation.

Effect of steam explosion pretreatment on the anaerobic digestion of rice straw

Rice straw pretreated under various conditions of temperature, ranging from 200 to 220 °C, and time, from 60 to 240 s, was used as the substrate in an anaerobic biogas recovery process. Steam explosion-pretreated rice straw displayed a significant improvement in physicochemical properties compared to untreated rice straw. The biogas production rate increased in all pretreated rice straw systems with shortened start-up periods, and the highest biogas production rate reached 328.7 mL g−1 TS (total solid content) under steam explosion pretreatment conditions of 200 °C/120 s, corresponding to a 51% increase. In addition, upon pretreatment at 200 °C/120 s, the degradation rates of cellulose and hemicellulose in the system reached 53.46% and 49.54%, which were 13.72% and 16.79% higher than in the control, respectively. PCR-DGGE analysis showed that the distributions of specific species of bacteria and archaea varied among different samples. There were clear differences in the bacterial population between pretreated and untreated groups during the set-up period and early stage. During the mid and final stages, pretreated systems had more diverse communities in the digester than the untreated system. Steam explosion pretreatment of the rice straw also led to the earlier presence of cellulolytic bacteria. Furthermore, the species of cellulolytic bacteria in pretreated systems were Clostridium sp. while those in the untreated reactor were Pseudomonas sp. The succession of archaea in the microbial community at different stages in the pretreated and untreated systems was not as obvious as that of bacteria. The results indicate that the physicochemical properties of rice straw were altered by the steam explosion pretreatment, which led to more efficient biogas production due to changes in the bacterial and archaeal species in the pretreated system.

Effects of different biofilm carriers on biogas production during anaerobic digestion of corn straw

This study investigated the performance of anaerobic digestion systems using four types of fibrous biofilm carriers, a polypropylene, a polyester, a polyamide, and a polyurethane fiber material. The biogas and methane production, pH, chemical oxygen demand, total solids content, volatile solids content, residual coenzyme F420, and microbial community compositions were determined during the experimental runs. Furthermore, scanning electron microscopy was employed to identify the microbial consortium and examine their attachment onto the surface of the four fibrous biofilm carriers. The polypropylene fiber system maintained the highest biogas and methane production in the reactor, which was 44.80% and 49.84% higher than that noted in the control, respectively, during the entire anaerobic fermentation cycle. Meanwhile, the polypropylene fiber system exhibited the highest TS, VS, and COD removal efficiency. The results of high-throughput sequencing indicated that the dominant species in the polypropylene fiber system were Methanoregula and Methanobacterium.

Ultrasonic and thermal pretreatments on anaerobic digestion of petrochemical sludge: Dewaterability and degradation of PAHs

Effects of different pretreatment methods on sludge dewaterability and polycyclic aromatic hydrocarbons (PAHs) degradation during petrochemical sludge anaerobic digestion were studied. Results showed that the total biogas production volume in the thermal pretreatment system was 4 and 5 times higher than that in the ultrasound pretreatment and in the control system, and the corresponding volatile solid removal efficiencies reached 28%, 15%, and 8%. Phenanthrene, paranaphthalene, fluoranthene, benzofluoranthene, and benzopyrene removal rates reached 43.3%, 55.5%, 30.6%, 42.9%, and 41.7%, respectively, in the thermal pretreatment system, which were much higher than those in the ultrasound pretreatment and in the control system. Moreover, capillary suction time (CST) of sludge increased after pretreatment, and then reduced after 20 days of anaerobic digestion, indicating that sludge dewaterability was greatly improved after anaerobic digestion. The decrease of protein and polysaccharide in the sludge could improve sludge dewaterability during petrochemical sludge anaerobic digestion. This study suggested that thermal pretreatment might be a promising enhancement method for petrochemical sludge solubilization, thus contributing to degradation of the PAHs, biogas production, and improvement of dewaterability during petrochemical sludge anaerobic digestion.

Effects of different carriers on biogas production and microbial community structure during anaerobic digestion of cassava ethanol wastewater

ABSTRACT In this study, an anaerobic bioreactor (AB) with no added fillers (ABWF), a packed-bed bioreactor with a porous ceramic filler (ABCF), and another packed-bed bioreactor filled with graphite felt (ABGF) were established for anaerobic digestion of cassava ethanol wastewater. The results showed that ABCF exhibited excellent wastewater treatment performance in a stable process that was superior to ABWF and ABGF, with the following characteristics: a high chemical oxygen demand removal efficiency of 98.06% and maximum biogas production of 3200 mL/d at a total reactor volume of 3.46 L. Illumina MiSeq sequencing analysis revealed that differences existed among the microbial communities of the three ABs that were in accordance with the operational characteristics. The ABCF system displayed maximum bacterial diversity, whereas the ABWF system exhibited moderate richness and the ABGF system possessed the lowest species richness. The ABCF system was more stable than the ABWF and ABGF systems during anaerobic digestion of cassava ethanol wastewater. Different functional microbial communities that are responsible for the degradation of certain compounds were also identified in the ABCF and ABGF systems. Our results demonstrate that ceramic materials should be considered an appropriate support for the immobilization of cells.

Anode modification by biogenic gold nanoparticles for the improved performance of microbial fuel cells and microbial community shift

In this study, carbon cloth anodes were modified using biogenic gold nanoparticles (BioAu) and nanohybrids of multi-walled carbon nanotubes blended with BioAu (BioAu/MWCNT) to improve the performance of microbial fuel cells (MFCs). The results demonstrated that BioAu modification significantly enhanced the electricity generation of MFCs. In particular, BioAu/MWCNT nanohybrids as the modifier displayed a better performance. The MFC with the BioAu/MWCNT electrode had the shortest start-up time (6.74 d) and highest power density (178.34 ± 4.79 mW/m2), which were 141.69% shorter and 56.11% higher compared with those of the unmodified control, respectively. These improvements were attributed to the excellent electrocatalytic activity and strong affinity towards exoelectrogens of the BioAu/MWCNT nanohybrids on the electrode. High throughput sequencing analysis indicated that the relative abundance of electroactive bacteria in the biofilm community, mostly from the classes of Gammaproteobacteria and Negativicutes, increased after anode modification.

Effect of MWCNT-modified graphite felts on hexavalent chromium removal in biocathode microbial fuel cells

Multi-walled carbon nanotubes (MWCNTs) and oxidative acid pretreated MWCNTs (oxidized MWCNTs, O-MWCNTs) were used to modify graphite felts as biocathode electrodes in Cr(VI)-reducing microbial fuel cells (MFCs). The results showed that both MWCNT modifications improved the efficiency of the Cr(VI)-reducing biocathode. In particular, the O-MWCNT modification led to a better performance due to the induced oxygen-containing functional groups on the O-MWCNTs. The O-MWCNT-modified graphite felt significantly promoted the Cr(VI) removal and electricity generation of the MFC. The Cr(VI) removal rate increased to 2.00 ± 0.10 mg L−1 h−1, which was 2.05 times higher than that of the unmodified control. The improvement was ascribed to the strong affinity and capacity of the O-MWCNTs towards microorganisms and Cr(VI) ions. In addition, this study further confirmed that the ex situ biocathode acclimatization method could be an efficient way to screen potential biocathode materials for Cr(VI)-reducing MFCs.

Genome sequence of a microbial lipid producing fungus Cryptococcus albidus NT2002

Cryptococcus albidus NT2002, isolated from the soil in Xinjiang, China, appeared to have the ability to accumulate microbial lipid by utilizing various carbon sources. The predominant properties make it as a potential bio-platform for biodiesel production. Here, we report the complete genome sequence of C. albidus NT2002, which might provide a basis for further elucidation of the genetic background of this promising strain for developing metabolic engineering strategies to produce biodiesel in a green and sustainable manner.