Continuous electricity production from leachate in a novel upflow air-cathode membrane-free microbial fuel cell

In this study, a novel microbial fuel cell, i.e. upflow air-cathode membrane-free microbial fuel cell (UAMMFC) was reported and its performance in electricity generation from original leachate was examined. The experimental results demonstrated that the UAMMFC could continuously generate electricity from leachate (0.3V; REX=150 Omega) for an operational period of time (50 h). The maximum volumetric power reached 12.8 W/m3 at current density of 41 A/m3 (93 Omega). NH4+-N elimination from the leachate was shown to be a consequence of electrochemistry-independent oxidation occurred in the MFC. Increasing organic loading rate from 0.65 to 5.2 kgCOD/m3 d resulted in a decrease of overall Coulombic efficiency (CE) from 14.4% to 1.2%. The low CE obtained here should be attributed to severe oxygen diffusion from the open-to-air cathode.

Assessing optimal fermentation type for bio-hydrogen production in continuous-flow acidogenic reactors

In this study, the optimal fermentation type and the operating conditions of anaerobic process in continuous-flow acidogenic reactors was investigated for the maximization of bio-hydrogen production using mixed cultures. Butyric acid type fermentation occurred at pH>6, propionic acid type fermentation occurred at pH about 5.5 with E(h) (redox potential) >-278mV, and ethanol-type fermentation occurred at pH<4.5. The representative strains of these fermentations were Clostridium sp., Propionibacterium sp. and Bacteriodes sp., respectively. Ethanol fermentation was optimal type by comparing the operating stabilities and hydrogen production capacities between the fermentation types, which remained stable when the organic loading rate (OLR) reached the highest OLR at 86.1kgCOD/m(3)d. The maximum hydrogen production reached up to 14.99L/d.

Biodegradation of pyridine using aerobic granules in the presence of phenol

Aerobic granules cultivated with 500 mg/L phenol medium effectively degraded pyridine at a concentration of 250-2500 mg/L; maximum degradation rate was 73.0 mg pyridineg/VSS/h at 250 mg/L pyridine concentration. Phenol concentrations of 500-2000 mg/L limited pyridine degradation in a competitive inhibition pattern, as interpreted using Michaelis-Menten kinetics with corresponding parameters V(max), K(m) and K(I) of 63.7 mg/Lh(-1), 827.8 and 1388.9 mg/L, respectively. Fluorescent staining and confocal laser scanning microscopy (CLSM) tests suggested that an active biomass accumulated at the granule outer layer. Denaturing gradient gel electrophoresis (DGGE) fingerprint profile demonstrated that dominating microbial strains exist in phenol and pyridine-degrading aerobic granules.

Synthesis of PHAs from waster under various C:N ratios

Polyhydroxyalkanoates (PHAs) production was carried out under various C:N ratios. A ratio of 100 resulted best polymer yield. C-source was an important factor in synthesis. For example, as the ratio of valeric acid (C5) to butyric acid (C4) in N-free medium was increased, the mole fraction of HV in the copolymer increased. When soy waste was used as a C-source a copolymer, a high HV mole fraction (HB:HV, 75:25) was produced while when malt waste was used, a much lower HV mole fraction (HB:HV, 90:10) was generated. It was concluded that activated sludge bacteria could be induced to produce PHAs using food wastes as C-sources and this could be the basis for production of biodegradable plastics.

Evaluation of heavy metal inhibition of activated sludge by TTC and INT-electron transport system activity tests

TTC and INT-electron transport system activity tests were compared for assessing heavy metal inhibition of activated sludge. The median inhibitory concentrations (IC50s) of Cu2+, Zn2+, Cd2+, Hg2+, Ni2+, Pb2+ and Ag+ measured via TTC test were lower than those measured via INT test, which indicates that the INT-electron transport system activity test was less sensitive to heavy metal toxicity than the TTC test. Tested heavy metals brought about similar decrease in TTC-electron transport system activity and COD removal rate, but less decrease in INT-electron transport system activity than COD removal rate, which suggests that the TTC-electron transport system activity is a better parameter for reflecting heavy metal inhibition of activated sludge than INT-electron transport system activity. The ranking of tested heavy metals in order of decreasing toxicity based on TTC test was Hg2+, Cd2+, Cu2+, Ag+, Zn2+, Ni2+ and Pb2+, and the ranking based on INT test was Hg2+, Ag+, Cu2+, Cd2+, Zn2+, Ni2+ and Pb2+.

Start-up of bio-hydrogen production reactor seeded with sewage sludge and its microbial community analysis

Start-up of a continuously stirred tank reactor for bio-hydrogen production under different initial organic loading rate (OLR) of 3, 7 and 10 kgCOD/m3 d, respectively, was carried out with sewage sludge as inoculum. Molasses wastewater was used as substrate and hydraulic retention time was kept at 6 h. This study aimed to assess OLR on the formation of fermentation types and the structure of microbial communities during the start-up period. It was found that at an initial OLR of 7 kgCOD/m3 d and an initial biomass of 6.24 gVSS/L, an equilibrial microbial community of ethanol-type fermentation could be established within 30 days. The observed average specific hydrogen production rate was 276 mLH2/gVSS d, which was 40% higher than that of the one acclimated with 3 kgCOD/m3 d. Based on denaturing gradient gel electrophoresis profiles, significant microbial population shifts took place at the first 15 days, but a longer period up to 30 days was required to establish a microbial community with stable metabolic activity.