Development of MFC using sulphonated polyether ether ketone (SPEEK) membrane for electricity generation from waste water

Polyether ether ketone was sulphonated polyether ether ketone (SPEEK) and utilized as a proton exchange membrane (PEM) in a single chamber MFC (SCMFC). The SPEEK was compared with Nafion? 117 in the SCMFC using Escherichia coli. The MFC with the SPEEK membrane produced 55.2% higher power density than Nafion? 117. The oxygen mass transfer coefficient (K(O)) for SPEEK and Nafion? 117 was estimated to be 2.4 × 10(-6)cm/s and 1.6 × 10(-5)cm/s, respectively resulting in reduced substrate loss and increased columbic efficiency (CE) in the case of SPEEK. When the dairy and domestic waste water was treated in SPEEK-SCMFC, fitted with a membrane electrode assembly (MEA), a higher maximum power density was obtained for dairy waste water (5.7 W/m(3)). The results of this study indicate that SPEEK membrane has the potential to greatly enhance the efficiency of MFCs.     

Microbial community structure and dynamics in a mixotrophic nitrogen removal process using recycled spent caustic under different loading conditions

A laboratory-scale Bardenpho process was established to investigate the proper nitrogen loading rate (NLR) when modified spent caustic (MSC) is applied as electron donor and alkalinity source for denitrification. MSC injection induced autotrophic nitrogen removal with sulfur as electron donor and heterotrophic denitrification. The nitrogen removal rate (NRR) did not increase proportionally to NLR. Based on the total nitrogen concentration in the effluent observed in the trials with MSC, the NLR in the influent should not exceed 0.15 kg N/m³ d in order to satisfy water quality regulations. Microbial communities in the anoxic reactors were characterized by pyrosequencing of 16S rRNA gene sequences amplified by the polymerase chain reaction of DNA extracted from sludge samples. Microbial diversity was lower as MSC dosage was increased, and the injection of MSC caused an increase in SOB belonging to the genus Thiobacillus which is responsible for denitrification using sulfur.     

Abundance of denitrifying genes coding for nitrate (narG), nitrite (nirS), and nitrous oxide (nosZ) reductases in estuarine versus wastewater effluent-fed constructed wetlands

Constructed and estuarine wetlands, influenced by wastewater treatment plants, were investigated, with respect to microbial activity in terms of functional genes. The density and abundance of three denitrifying genes coding for nitrate (narG), nitrite (nirS), and nitrous oxide (nosZ) reductases, in sediment soil samples from wastewater effluent-fed and estuarine wetlands, were quantified using the SYBR green-based real-time polymerase chain reaction (PCR). To assess seasonal effects (i.e., winter (average temperature ∼2 °C) versus spring (average temperature ∼20 °C)), the densities of denitrifying genes, with respect to the abundance of functional genes, for the two different wetlands were determined. The three functional genes for all the sampling sites ranged from 1.0 × 10⁶ to 1.0 × 10⁹ copies/g of soil. Without considering seasonal variation, the nitrite-reducing functional genes were dominant over the other two genes in the effluent-fed wetland samples. However, nitrate and nitrite-reducing functional genes were dominant in relatively cold and warm seasons, respectively, in the estuarine wetland samples. Even though robust patterns and conclusions could not be obtained from the limited investigations, patterns with certain trends and needs for potential future research directions were obtained.     

Microbial population dynamics during sludge granulation in an anaerobic-aerobic biological phosphorus removal system

The evolution of a microbial community was investigated during sludge granulation using a wide range of micro-scale and molecular biology techniques. Experimental results demonstrate that polyphosphate-accumulating granules were successfully cultured during the anaerobic/aerobic cycle. Improvement in sludge sedimentation performance occurred prior to the formation of granular sludge and was not affected by change in granule size. Rod-shaped and filamentous bacteria appeared to initiate granule formation and generate the structures that supported further granule growth. It was observed that mature granules supported microbial populations that differed from nascent granules and were predominantly packed with coccoid bacteria. It was further observed that the diversity of the granular microbial community increased as the granules grew. Accumulibacter, Nitrosospira and Thauera were mainly responsible for nutrient removal while microorganisms such as Rhodocyclus and Hyphomicrobiaceae appeared to be primarily responsible for forming and maintaining the granule structure.     

Enhancement in current density and energy conversion efficiency of 3-dimensional MFC anodes using pre-enriched consortium and continuous supply of electron donors

Using a pre-enriched microbial consortium as the inoculum and continuous supply of carbon source, improvement in performance of a three-dimensional, flow-through MFC anode utilizing ferricyanide cathode was investigated. The power density increased from 170 W/m³ (1800 mW/m²) to 580 W/m³ (6130 mW/m²), when the carbon loading increased from 2.5 g/l-day to 50 g/l-day. The coulombic efficiency (CE) decreased from 90% to 23% with increasing carbon loading. The CEs are among the highest reported for glucose and lactate as the substrate with the maximum current density reaching 15.1 A/m². This suggests establishment of a very high performance exoelectrogenic microbial consortium at the anode. A maximum energy conversion efficiency of 54% was observed at a loading of 2.5 g/l-day. Biological characterization of the consortium showed presence of Burkholderiales and Rhodocyclales as the dominant members. Imaging of the biofilms revealed thinner biofilms compared to the inoculum MFC, but a 1.9-fold higher power density.     

Autotrophic nitrite removal in the cathode of microbial fuel cells

Nitrification to nitrite (nitritation process) followed by reduction to dinitrogen gas decreases the energy demand and the carbon requirements of the overall process of nitrogen removal. This work studies autotrophic nitrite removal in the cathode of microbial fuel cells (MFCs). Special attention was paid to determining whether nitrite is used as the electron acceptor by exoelectrogenic bacteria (biologic reaction) or by graphite electrodes (abiotic reaction). The results demonstrated that, after a nitrate pulse at the cathode, nitrite was initially accumulated; subsequently, nitrite was removed. Nitrite and nitrate can be used interchangeably as an electron acceptor by exoelectrogenic bacteria for nitrogen reduction from wastewater while producing bioelectricity. However, if oxygen is present in the cathode chamber, nitrite is oxidised via biological or electrochemical processes. The identification of a dominant bacterial member similar to Oligotropha carboxidovorans confirms that autotrophic denitrification is the main metabolism mechanism in the cathode of an MFC.     

Transition of microbial communities during the adaption to anaerobic digestion of carrot waste

In this study a microbial community suitable for anaerobic digestion of carrot pomace was developed from inocula obtained from natural environmental sources. The changes along the process were monitored using pyrosequencing of the 16S rRNA gene. As the community adapted from a diverse natural community to a community with a definite function, diversity decreased drastically. Major bacterial groups remaining after enrichment were Bacilli (31-45.3%), Porphyromonadaceae (12.1-24.8%) and Spirochaetes (12.5-18.5%). The archaeal population was even less diverse and mainly represented by a single OTU that was 99.7% similar to Methanosarcina mazei. One enrichment which failed to produce large amounts of methane had shifts in the bacterial populations and loss of methanogenic archaea.     

Linking microbial community structure to membrane biofouling associated with varying dissolved oxygen concentrations

In order to elucidate how dissolved oxygen (DO) concentration influenced the generation of extracellular polymeric substance (EPS) and soluble microbial products (SMP) in mixed liquor and biocake, 16S rDNA fingerprinting analyses were performed to investigate the variation of the microbial community in an aerobic membrane bioreactor (MBR). The function of microbial community structure was proved to be ultimately responsible for biofouling. Obvious microbial community succession from the subphylum of Betaproteobacteria to Deltaproteobacteria was observed in biocake. High concentration of EPS in biocake under the low DO concentration (0.5 mg L⁻¹) caused severe biofouling. The correlation coefficient of membrane fouling rate with EPS content in biocake (0.9941-0.9964) was much higher than that in mixed liquor (0.6689-0.8004).     

Enhancement of methane production from cassava residues by biological pretreatment using a constructed microbial consortium

In the study, a stable thermophilic microbial consortium with high cellulose-degradation ability was successfully constructed. That several species of microbes coexisted in this consortium was proved by DGGE (denaturing gradient gel electrophoresis) and sequence analysis. The cooperation and symbiosis of these microbes in this consortium enhanced their cellulose-degradation ability. The pretreatment of cassava residues mixing with distillery wastewater prior to anaerobic digestion was investigated by using this microbial consortium as inoculums in batch bioreactors at 55 °C. The experimental results showed that the maximum methane yield (259.46 mL/g-VS) of cassava residues was obtained through 12 h of pretreatment by this microbial consortium, which was 96.63% higher than the control (131.95 mL/g-VS). In addition, it was also found that the maximum methane yield is obtained when the highest filter paper cellulase (FPase), carboxymethyl cellulase (CMCase) and xylanase activity and soluble COD (sCOD) are produced.