Effects of microbial species, organic loading and substrate degradation rate on the power generation capability of microbial fuel cells.

Four microbial fuel cells (MFCs) inoculated with different bacterial species were constructed. The species were Pseudomonas putida, Comamonas testosteroni, Corynebacterium gultamicum, and Arthrobacter polychromogenes. The MFCs were operated under identical continuous flow conditions. The factors affecting the capabilities of the MFCs for treating organic matter and generating power were evaluated and compared. The factors include microbial species type, organic loading, and substrate degradation rate. For all four MFCs, power output increased with the organic loading rate. Power density also increased with the substrate degradation rate. These findings implied that more organic matter was utilized for power generation at higher organic loading and substrate degradation rates. However, coulombic efficiency increased with decreased organic loading and substrate degradation rates. Apparently, all four MFCs had low efficiencies in generating power from organic matter. These low efficiencies are attributed to the long distance between the anode and the cathode, as well as to the small ratio of the proton exchange membrane surface area to the anode chamber surface area. These features may have caused most of the protons produced in the anode chamber to leave the chamber with the effluent, which led to the low power generation performance of the MFCs.

Effects of synthetic polymer on the filamentous bacteria in activated sludge.

Filamentous bulking is one of the solid-liquid separation problems always seen in activated sludge process. The addition of synthetic polymer is always one of the popular ways for the treatment plant operator to immediately solve the poor sludge settling problem. Therefore, it may be interesting to understand the effects of synthetic polymer on the filamentous bacteria in activated sludge. In this study, synthetic polymer was applied to a lab-scale wastewater treatment system with the filamentous bulking problem. The population structure of filamentous bacteria and sludge characteristics were investigated under different conditions. When synthetic polymer was added into the system, it was found that poor sludge settleability caused by filamentous bulking was temporarily solved and filamentous branches growing outside the flocs were damaged or inhibited. However, filamentous growth was still observed inside the flocs. After the addition of polymer was halted, filamentous branches extended out of the flocs immediately. Very serious filamentous bulking occurred and sludge settleability became much worse than that occurring before the addition of polymer. And, it took several weeks for the system to return to normal operation.

Power generation capabilities of microbial fuel cells with different oxygen supplies in the cathodic chamber.

Two microbial fuel cells (MFCs) inoculated with activated sludge of a wastewater treatment plant were constructed. Oxygen was provided by mechanical aeration in the cathodic chamber of one MFC, whereas it was obtained by the photosynthesis of algae in the other. Electrogenic capabilities of both MFCs were compared under the same operational conditions. Results showed that the MFC with mechanical aeration in the cathodic chamber displayed higher power output than the one with photosynthesis of algae. Good linear relationship between power density and chemical oxygen demand (COD) loading rate was obtained only on the MFC with mechanical aeration. Furthermore, the relationships between power density and effluent COD and between Coulombic efficiency and COD loading rate can only be expressed as binary quadratic equations for the MFC with mechanical aeration and not for the one with photosynthesis of algae.

Do the VOCs that evaporate from a heavily polluted river threaten the health of riparian residents?

To understand the potential threat of volatile organic compounds (VOCs) to the health of residents living close to a heavily polluted river, this study investigated the species and the concentration of VOCs evaporating from a river and surveyed the health condition of the nearby residents. Air samples were taken seasonally at the upstream, midstream, and downstream water surfaces of the river, and at different locations at certain distances from the river. These samples were analyzed qualitatively and quantitatively through gas chromatography and electron capture detector (GC/ECD) for chlorinated organic compounds, and through gas chromatography and flame ionization detector (GC/FID) for ordinary hydrocarbons. The health data obtained from valid health questionnaires of 908 residents were analyzed through Statistical Package for Social Science (SPSS) software. Twenty-six species of VOCs were identified in the environment adjacent the river, many of which are carcinogenic or believed to be carcinogenic to humans. However, results of this study shows that the VOCs evaporating from the polluted river have not been definitively identified as a major factor of cancer in the residents. However, the risk of suffering from certain chronic diseases may increase in residents living less than 225 m away from the river due to the high levels of evaporated VOCs. Residents living less than 225 m away from the river and with nearby specific industries are 3.130 times more at risk of suffering from chronic diseases than those with no nearby specific industries.