Functionally stable and phylogenetically diverse microbial enrichments from microbial fuel cells during wastewater treatment

Microbial fuel cells (MFCs) are devices that exploit microorganisms as biocatalysts to recover energy from organic matter in the form of electricity. One of the goals of MFC research is to develop the technology for cost-effective wastewater treatment. However, before practical MFC applications are implemented it is important to gain fundamental knowledge about long-term system performance, reproducibility, and the formation and maintenance of functionally-stable microbial communities. Here we report findings from a MFC operated for over 300 days using only primary clarifier effluent collected from a municipal wastewater treatment plant as the microbial resource and substrate. The system was operated in a repeat-batch mode, where the reactor solution was replaced once every two weeks with new primary effluent that consisted of different microbial and chemical compositions with every batch exchange. The turbidity of the primary clarifier effluent solution notably decreased, and 97% of biological oxygen demand (BOD) was removed after an 8-13 day residence time for each batch cycle. On average, the limiting current density was 1000 mA/m(2), the maximum power density was 13 mW/m(2), and coulombic efficiency was 25%. Interestingly, the electrochemical performance and BOD removal rates were very reproducible throughout MFC operation regardless of the sample variability associated with each wastewater exchange. While MFC performance was very reproducible, the phylogenetic analyses of anode-associated electricity-generating biofilms showed that the microbial populations temporally fluctuated and maintained a high biodiversity throughout the year-long experiment. These results suggest that MFC communities are both self-selecting and self-optimizing, thereby able to develop and maintain functional stability regardless of fluctuations in carbon source(s) and regular introduction of microbial competitors. These results contribute significantly toward the practical application of MFC systems for long-term wastewater treatment as well as demonstrating MFC technology as a useful device to enrich for functionally stable microbial populations.     

Effects of stratification in a fluidized bed bioreactor during treatment of metalworking wastewater

During wastewater treatment, biofilm-coated sand particles stratified in a fluidized bed bioreactor (FBB); particles coated by thicker biofilm segregated toward the top of the bed. Stratification was so well developed that at least two co-existing regions of significantly different mean biofilm thickness were visually distinct within the operating FBB. The observed stratification is attributed to differences in forces of drag, buoyancy, shear, and collisional impact, as well as differences of collision rate within the different regions. Particles with thick biofilm (thickness >100 μm) near the top of the bed consumed substrate at significantly lower rates per unit biomass than particles with thin biofilm (10-20 μm) near the bottom of the bed, thereby suggesting that substrate mass-transfer resistance through biofilm may limit biodegradation rates in the upper portion of the FBB. Large agglomerates of biomass floc and sand, which formed at the top of the fluidized bed, and sand particles with thick biofilm were susceptible to washout from the FBB, causing operational and treatment instability. Radial injection of supplemental liquid feed near the top of the bed increased shear and mixing, thereby preventing formation and washout of agglomerates and thickly coated sand particles. Supplemental liquid injection caused the mean specific biomass loading on the sand to increase and also increased the total biomass inventory in the FBB. Rates of biodegradation in the FBB appeared to be limited by penetration of substrates into the biofilm and absorption of oxygen from air into the wastewater. Copyright 1999 John Wiley & Sons, Inc.     

Packed cage rotating biological contactor system for treatment of cyanide wastewater

The aim of this work was to study the efficiency of the packed cage rotating biological contactor (RBC) system with synthetic wastewater (SWW) containing 800 mg/l BOD(5) with various cyanide residue concentrations and hydraulic loading time. The results showed that cyanide had a negative effect to both the system's efficiency and bio-film quality. An increase in cyanide concentration led to a decrease in bio-film growth and the consequent reduction in the removal efficiency of the system. Also, the effluent suspended solids (SS) of the system was increased with increasing cyanide concentrations because the bio-film detached from the media due to the toxicity of the cyanide residue. The system showed the highest COD, BOD(5), TKN and cyanide removal efficiencies of 94.0 +/- 1.6%, 94.8 +/- 0.9%, 59.1 +/- 2.8% and 95.5 +/- 0.6%, respectively, with SWW containing 5 mg/l cyanide under HRT of 8 days, while they were only 88.8 +/- 0.7%, 89.5 +/- 0.5%, 40.3 +/- 1.1% and 93.60 +/- 0.09%, respectively, with SWW containing 40 mg/l cyanide. In addition, the effluent ammonia, nitrite and nitrate were increased with increases in cyanide concentration or loading. However, the system with SWW containing the highest cyanide concentration of 40 mg/l showed almost constant COD and BOD(5) removal efficiencies of 89% and 90%, even when the system was controlled under the lowest HRT of 8 h.     

Standards for molecular dynamics modelling and simulation of relaxation

An attempt is made to formulate a set of requirements for simulation and modelling of relaxation in dense media. Each requirement is illustrated by examples of numerical simulation of particles with different types of interaction given by soft-sphere, Lennard–Jones, embedded atom method or Coulomb potential. The approaches developed are expected to be universal for some classes of relaxation processes in liquids, fluids, crystals and plasmas.     

Stratified microbial structure and activity within anode biofilm during electrochemically assisted brewery wastewater treatment

In a bioelectrochemical system (BES), microbial community of anode biofilm is crucial to BES performance. In this study, the stratified pattern of community structure and activity of an anode-respiring biofilm in a BES fueled with brewery wastewater was investigated over time. The anode biofilm exhibited a superior performance in the removal of ethanol to that of an open-circuit system. The electrical current density reached a high level of 0.55mA/cm² with a Coulombic efficiency of 71.4%, but decreased to 0.18mA/cm² in the late stage of operation. A mature biofilm developed a more active outer layer covering a less active inner core, although the activities of the outer and inner layers of biofilm were similar in the early stage. More Geobacter spp., typical exoelectrogens, were enriched in the outer layer than in the inner layer of biofilm in the early stage, while more Geobacter spp. were distributed in the inner layer than in the outer layer in the late stage. The inactive and Geobacter-occupied inner layer of biofilm might be responsible for the decreased electricity generation from wastewater in the late stage of operation. This study provides better understanding of the effect of anode biofilm structure on BES performance.     

Sustainable wastewater treatment: How might microbial fuel cells contribute

The need for cost-effective low-energy wastewater treatment has never been greater. Clean water for our expanding and predominantly urban global population will be expensive to deliver, eats into our diminishing carbon-based energy reserves and consequently contributes to green house gases in the atmosphere and climate change. Thus every potential cost and energy cutting measure for wastewater treatment should be explored. Microbial fuel cells (MFCs) could potentially yield such savings but, to achieve this, requires significant advances in our understanding in a few critical areas and in our designs of the overall systems. Here we review the research which might accelerate our progress towards sustainable wastewater treatment using MFCs: system control and modelling and the understanding of the ecology of the microbial communities that catalyse the generation of electricity.     

Adaptation and population dynamics of Azotobacter vinelandii during aerobic biological treatment of olive-mill wastewater

Olive-mill wastewater (OMW) has a high organic and polyphenol content and is resistant to biodegradation. Its disposal leads to a major environmental pollution problem in the Mediterranean basin. The detoxification of OMW following inoculation with Azotobacter vinelandii (strain A) was performed for two successive 5-day-period cycles in an aerobic, biowheel-type reactor, under non-sterile conditions. The phytotoxicity of the processed product was reduced by over 90% at the end of both cycles. To exclusively monitor the A. vinelandii population in the reactor a most probable number-PCR approach was employed and applied daily to serial dilutions of total DNA extracted from reactor samples. PCR sensitivity was independent of the presence of OMW or non-target DNA. The A. vinelandii population dynamics were successfully monitored, showing an initial adaptation period, followed by a sharp population maximum on the fourth day of both cycles (1.6x10(8) and 9.6x10(7) cells ml(-1) respectively), after a major phytotoxicity decline. N(2) fixation rates were estimated using the acetylene reduction assay and reached a peak during the first 1-2 days of each cycle (36 and 29 nmol C(2)H(2) ml(-1) h(-1) respectively). The data are consistent with an initial physiological adaptation phase, where the presence of phenolic compounds limits A. vinelandii growth but stimulates N(2) fixation, followed by a rapid growth phase as phytotoxicity declines.     

Anaerobic treatment of winery wastewater in fixed bed reactors

The treatment of winery wastewater in three upflow anaerobic fixed-bed reactors (S9, S30 and S40) with low density floating supports of varying size and specific surface area was investigated. A maximum OLR of 42 g/l day with 80 ± 0.5% removal efficiency was attained in S9, which had supports with the highest specific surface area. It was found that the efficiency of the reactors increased with decrease in size and increase in specific surface area of the support media. Total biomass accumulation in the reactors was also found to vary as a function of specific surface area and size of the support medium. The Stover–Kincannon kinetic model predicted satisfactorily the performance of the reactors. The maximum removal rate constant (U _max) was 161.3, 99.0 and 77.5 g/l day and the saturation value constant (K _B) was 162.0, 99.5 and 78.0 g/l day for S9, S30 and S40, respectively. Due to their higher biomass retention potential, the supports used in this study offer great promise as media in anaerobic fixed bed reactors. Anaerobic fixed-bed reactors with these supports can be applied as high-rate systems for the treatment of large volumes of wastewaters typically containing readily biodegradable organics, such as the winery wastewater.     

Alternative electron acceptors in microbial coal-conversion wastewater treatment

Biotreatment experiments with solutions of autoxidized phenolic compounds as well as coal-conversion wastewater stored for 30 years and rich in humic matter were performed under nitrate-reducing, sulphate-reducing and methanogenic conditions. The removal of total organic carbon in fractions of different molecular mass and of monomeric phenolic compounds in the wastewater was determined. A comparison of biotransformation potentials and rates indicated a relationship between these aspects and the availability of electron acceptors in the system. The capacities of the microbial consortia increased significantly with the energy microorganisms could gain from their respective respiration process and can be expressed by the order: aerobic process – nitrate reduction – sulphate reduction – methanogenesis. Received: 25 April 1996 / Received revision: 23 July 1996 / Accepted: 5 August 1996.     

Innovative graphene microbial platforms for domestic wastewater treatment

Supplying clean water to fulfill human requirements is one of this century’s priorities. Global water resources are barely aligned with the rising demand, which is further aggravated by rising population, climate change and water quality problems. Consequently, there is a persistent need for innovative technologies to valorize unconventional water resources such as domestic wastewater. Graphene holds promising prospects in developing domestic wastewater treatment to qualitatively enhance treatment efficiency and quantitatively increase water supply. This review highlights the existing wastewater treatment processes along with their challenges according to South Australian wastewater treatment plants (WWTPs) which are representative of many modern WWTPs. The discussion will also cover the current and potential applications of graphene for domestic wastewater treatment, as well as obstacles and research priorities required for commercialization.     

High-strength wastewater treatment using microbial biofilm reactor: a critical review

World Journal of Microbiology and Biotechnology - Natural products extracted from plants are an alternative method for controlling postharvest citrus blue mold, caused by Penicillium italicum (P....     

Development of a microbial consortium for dairy wastewater treatment

The wastewater from the dairy industries usually contains high concentrations of contaminants and, since the volume generated is also high, the total contaminant load is very significant. Among the available options for treatment, biological degradation looks like the most promising one. Furthermore, the supplementation of the native microbial populations with external microorganisms with high specific degradation rates (bio-augmentation) has demonstrated to improve the performance of treatment. The main objective of this research was to select a combination of bacteria to improve the aerobic treatment of dairy processing wastewater. For this purpose, eleven fat/protein-degrading microorganisms belonging to the genera Bacillus, Serratia, Lactococcus, Enterococcus, Stenotrophomonas, Klebsiella and Escherichia, were evaluated as potential degrading bacteria using a Plackett-Burman design. Assays were carried out to select the strains that most significantly influenced the degradation of wastewater and biomass yield, in terms of COD removal. A simulated dairy industry effluent was used as culture medium. Four strains were selected as potential members of the microbial consortium: Lactococcus garvieae, Bacillus thuringiensis, Escherichia coli and Stenotrophomonas sp. The optimal operation temperature and pH range of the selected consortium were 32°C and 6 ～ 8, respectively. The degradation percentages reached with the selected consortium were 80.67 and 83.44% at 24 and 48 h, respectively. The selected consortium significantly improved the degradation of the dairy wastewater, and the degradation degree achieved by this consortium was higher than by using the strains individually.     

Brewery wastewater treatment using anaerobic inverse fluidized bed reactors

Two anaerobic inverse fluidized bed reactors were utilized to evaluate organic matter removal from brewery wastewater, applying different OLR and testing two support materials. Hydrodynamic tests varying liquid flow and solid concentration were developed on the supports in order to establish operational conditions. A batch colonization stage was applied using 25% active volume of extendosphere and triturated polyethylene as support materials. The reactors were subsequently operated continuously with stepwise increments in organic loading rate until limiting conditions was reached. For the supports studied, IFBR technology was suitable for organic matter removal present in brewery wastewater with COD removal efficiencies greater than 90%. The reactor with triturated polyethylene support showed an excellent COD removal with OLR values up to 10 g COD/Ld, whereas the reactor with extendosphere support had an excellent hydrodynamic and biologic behavior working with OLR values up to 70 g COD/Ld.     

微生物絮凝剂在养殖废水处理中的应用

微生物絮凝剂作为一种新型的絮凝剂,因其安全、高效等特性,正逐渐成为目前水产养殖废水处理研究的热点。主要从微生物絮凝剂的概念、絮凝机理、特点、研究现状、应用实例等方面,分析了微生物絮凝剂作为水质改良剂在水产养殖中的应用前景,并就今后的研究趋势作了展望。     

Stackable and submergible microbial fuel cell modules for wastewater treatment

The stackable and submergible microbial fuel cell (SS-MFC) system was fabricated consisting of three MFC modules (#1, #2 and #3) that were immersed in an anaerobic tank as a 30 L anode compartment. Each module consisted of the anion exchange membrane–membrane electrode assembly (A-MEA) and cation exchange membrane-MEA (C-MEA). Two MEAs shared a cathode compartment in the module and the three modules shared a anode compartment The SS-MFC system was operated with two phase. After batch feeding (phase I), the system was operated under continuous mode (phase II) with different organic concentrations (from 50 to 1000 mg/L) and different hydraulic retention times (HRT; from 3.4 to 7.2 h). The SS-MFC system successfully produced a stable voltage. A-MEA generated a lower power density than the C-MEA because of the former’s high activation and resistance loss. C-MEA showed a higher average maximum power density (3.16 W/m³) than A-MEA (2.82 W/m³) at 70 mL/min (HRT of 7.2 h). The current density increased as the organic concentration was increased from 70 to 1000 mg/L in a manner consistent with Monod kinetics. When the HRT was increased from 3.4 to 7.2 h, the power densities of the C-MEAs increased from 34.3–40.9 to 40.7–45.7 mW/m², but those of the A-MEAs decreased from 25.3–48.0 to 27.7–40.9 mW/m². Although power generation was affected by HRT, organic concentrations, and separator types, the proposed SS-MFC modules can be applied to existing wastewater treatment plants.     

Rhizosphere dynamics during phytoremediation of olive mill wastewater

The potential of phytoremediation as a treatment option for olive mill wastewater (OMW) was tested on five perennial tree species. Cupressus sempervirens and Quercus ilex proved tolerant to six-month OMW treatment followed by six-month water irrigation, whereas Salix sp. and Laurus nobilis and, later, Pinus mugo suffered from phytotoxic effects. Test plants were compared to controls after treatment and irrigation, by monitoring biochemical and microbiological variations in the rhizosphere soil. OMW-treated soils were exposed to 50-fold higher phenols concentrations, which, irrespective of whether the respective plants were OMW-resistant or susceptible, were reduced by more than 90% by the end of the irrigation cycle, owing to significantly increased laccase, peroxidase and β-glucosidase activities, recovery/acquisition of bacterial culturability and transitory development of specialized fungal communities sharing the presence of Geotrichum candidum. Of all results, the identification of Penicillium chrysogenum and Penicillium aurantiogriseum as dominant rhizosphere fungi was distinctive of OMW-tolerant species.     

Composition and dynamics of microbial community in a zeolite biofilter-membrane bioreactor treating coking wastewater

In this study, a lab-scale anaerobic/anoxic/zeolite biofilter-membrane bioreactor (A₁/A₂/ZB-MBR) was designed to treat coking wastewater. The 454 pyrosequencing was used to obtain the composition and dynamics of microbial community about the treatment system. The results showed that the system yielded stable effluent chemical oxidation demand (158.5?±?21.8 mg/L) and ammonia (8.56?±?7.30 mg/L), but fluctuant total nitrogen (31.4–165.1 mg/L) concentrations. In addition, 66,256 16S rRNA gene sequences were obtained from A₂ and ZB-MBR, and the microbial diversity and richness for five samples were determined. Although community compositions in the five samples were quite different, bacteria assigned to phylum Proteobacteria and class Flavobacteria commonly existed and dominated the microbial populations. The pyrosequencing analysis revealed that the microbial community shifted in the ZB-MBR with the presence of zeolite. Some taxa began to appear in ZB-MBR and contributed to the system performance. Additionally, Nitrosomonas and Nitrobacter gradually became the dominant ammonia-oxidizing bacteria and nitrite-oxidizing bacteria during the operation, respectively, which are favorable for the stabilized ammonia removal. Our results proved that the ZB-MBR is an alternative technique for treating coking wastewater.     

The dynamics of climate-induced range shifting; perspectives from simulation modelling

Predicted future climate change will alter species' distributions as they attempt to track the most suitable 'climate window'. Climate envelope models indicate the direction of likely range changes but do not incorporate population dynamics, therefore observed responses may differ greatly from these projections. We use simulation modelling to explore the consequences of a period of environmental change for a species structured across an environmental gradient. Results indicate that a species' range may lag behind its climate envelope and demonstrate that the rate of movement of a range can accelerate during a period of climate change. We conclude that the inclusion of both population dynamics and spatial environmental variability is vital to develop models that can both predict, and be used to manage, the impact of changing climate on species' biogeography.