Microbial fuel cells (MFCs) have been conceived and intensively studied as a promising technology to achieve sustainable wastewater treatment. However, doubts and debates arose in recent years regarding the technical and economic viability of this technology on a larger scale and in a real-world applications. Hence, it is time to think about and examine how to recalibrate this technology's role in a future paradigm of sustainable wastewater treatment. In the past years, many good ideas/approaches have been proposed and investigated for MFC application, but information is scattered. Various review papers were published on MFC configuration, substrates, electrode materials, separators and microbiology but there is lack of critical thinking and systematic analysis of MFC application niche in wastewater treatment. To systematically formulate a strategy of (potentially) practical MFC application and provide information to guide MFC development, this perspective has critically examined and discussed the problems and challenges for developing MFC technology, and identified a possible application niche whereby MFCs can be rationally incorporated into the treatment process. We propose integration of MFCs with other treatment technologies to form an MFC-centered treatment scheme based on thoroughly analyzing the challenges and opportunities, and discuss future efforts to be made for realizing sustainable wastewater treatment.

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Towards sustainable wastewater treatment by using microbial fuel cells-centered technologies

Geobacter species specialize in making electrical contacts with extracellular electron acceptors and other organisms. This permits Geobacter species to fill important niches in a diversity of anaerobic environments. Geobacter species appear to be the primary agents for coupling the oxidation of organic compounds to the reduction of insoluble Fe(III) and Mn(IV) oxides in many soils and sediments, a process of global biogeochemical significance. Some Geobacter species can anaerobically oxidize aromatic hydrocarbons and play an important role in aromatic hydrocarbon removal from contaminated aquifers. The ability of Geobacter species to reductively precipitate uranium and related contaminants has led to the development of bioremediation strategies for contaminated environments. Geobacter species produce higher current densities than any other known organism in microbial fuel cells and are common colonizers of electrodes harvesting electricity from organic wastes and aquatic sediments. Direct interspecies electron exchange between Geobacter species and syntrophic partners appears to be an important process in anaerobic wastewater digesters. Functional and comparative genomic studies have begun to reveal important aspects of Geobacter physiology and regulation, but much remains unexplored. Quantifying key gene transcripts and proteins of subsurface Geobacter communities has proven to be a powerful approach to diagnose the in situ physiological status of Geobacter species during groundwater bioremediation. The growth and activity of Geobacter species in the subsurface and their biogeochemical impact under different environmental conditions can be predicted with a systems biology approach in which genome-scale metabolic models are coupled with appropriate physical/chemical models. The proficiency of Geobacter species in transferring electrons to insoluble minerals, electrodes, and possibly other microorganisms can be attributed to their unique "microbial nanowires," pili that conduct electrons along their length with metallic-like conductivity. Surprisingly, the abundant c-type cytochromes of Geobacter species do not contribute to this long-range electron transport, but cytochromes are important for making the terminal electrical connections with Fe(III) oxides and electrodes and also function as capacitors, storing charge to permit continued respiration when extracellular electron acceptors are temporarily unavailable. The high conductivity of Geobacter pili and biofilms and the ability of biofilms to function as supercapacitors are novel properties that might contribute to the field of bioelectronics. The study of Geobacter species has revealed a remarkable number of microbial physiological properties that had not previously been described in any microorganism. Further investigation of these environmentally relevant and physiologically unique organisms is warranted.

Geobacter: The Microbe Electric's Physiology, Ecology, and Practical Applications

Recent trends in biodegradable polymers indicate significant developments in terms of novel design strategies and engineering to provide advanced polymers with comparably good performance. However, there are several inadequacies in terms of either technology or cost of production especially in the case of applications in environmental pollution. So, there is a need to have a fresh perspective on the design, properties and functions of these polymers with a view to developing strategies for future developments. The paper reviews the present state-of-art on biodegradable polymers and discusses the salient features of the design and properties of biodegradable polymers. Special emphasis is given to the problems and prospects of (1) approaches adopted to make non-biodegradable synthetic polymers such as polyethylene biodegradable and (2) biodegradable polymers and copolymers made from renewable resources especially poly(lactic acid) based polymers and copolymers which are emerging as the candidate biodegradable materials for the future.

Biodegradable Polymers- A Review on Recent Trends and Emerging Perspectives

Microplastics are widespread contaminants, virtually present in all environmental compartments. However, knowledge on sources, fate and environmental concentration over time and space still is limited due to the laborious and varied analytical procedures currently used. In this work we critically review the methods currently used for sampling and detection of microplastics, identifying flaws in study design and suggesting promising alternatives. This work provides insights on bulk sample collection, separation, digestion, identification and quantification, and mitigation of cross-contamination. The sampling of microplastics will improve in representativeness and reproducibility through the determination of bulk sample volume, filter's pore size, density separation and digestion solutions, but also through use of novel methods, such as the enhancement of visual identification by staining dyes, and the generalized use of chemical characterization.

Methods for sampling and detection of microplastics in water and sediment: A critical review

A New Perspective on Microbes Formerly Known as Nitrite-Oxidizing Bacteria

Humic acids (HAs) content of raw water is an important analytical parameter in water treatment facilities because HAs in the presence of chlorine may lead to the formation of dangerous by-products (e.g., trihalomethanes). The concentration of HAs in water is not directly accessible by common analytical methods due to their heterogeneous chemical structure. The aim of this study was to compare two methods to assess humic acids (HAs) in surface water namely absorbance of ultraviolet light at 254 nm (UV254) and total organic carbon (TOC), as well as to evaluate the effects of calcium and magnesium concentrations, pH and sample filtration on the methods' results. An aqueous solution of a commercial HA with 10 mg L−1 was used in the present work. Quantification of the HA was carried out by both UV254 and TOC (combustion-infrared method) measurements. UV254 results were converted to TOC using a calibration curve. The effects of calcium (0–136.3 mg L−1) and magnesium (0–34.5 mg L−1) concentrations, pH (4.0, 7.0 and 9.0) and sample filtration on UV254 and TOC measurements of the HA suspension were evaluated. More accurate TOC values of HA suspensions were obtained by the combustion-infrared method than by the UV254 absorbance method. The higher differences of TOC values between unfiltered and filtered samples were detected in the presence of calcium at pH 9.0 using the spectrophotometric method.

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Quantification of humic acids in surface water: effects of divalent cations, pH, and filtration.

https://repositorium.sdum.uminho.pt/bitstream/1822/7536/1/Ribeiro_Chemosphere%5b2%5d.pdf

Phosphorus fractionation in volcanic lake sediments (Azores - Portugal).

In this work the question was addressed if in nitrite-oxidizing activated sludge systems the environmental competition between Nitrobacter spp. and Nitrospira spp., which only recently has been discovered to play a role in these systems, is affected by the nitrite concentrations. Two parallel chemostats were inoculated with nitrifying-activated sludge containing Nitrospira and operated under identical conditions. After addition of Nitrobacter to both chemostats, the nitrite concentration in the influent of one of the chemostats was increased such that nitrite peaks in the bulk liquid of this reactor were detected. The other chemostat served as control reactor, which always had a constant nitrite influent concentration. The relative cellular area (RCA) of Nitrospira and Nitrobacter was determined by quantitative fluorescence in situ hybridization (FISH). The nitrite perturbation stimulated the growth of Nitrobacter while in the undisturbed control chemostat Nitrospira dominated. Overall, the results of this experimental study support the hypothesis that Nitrobacter is a superior competitor when resources are abundant, while Nitrospira thrive under conditions of resource scarcity. Interestingly, the dominance of Nitrobacter over Nitrospira, caused by the elevated nitrite concentrations, could not be reverted by lowering the available nitrite concentration to the original level. One possible explanation for this result is that when Nitrobacter is present at a certain cell density it is able to inhibit the growth of Nitrospira. An alternative explanation would be that the length of the experimental period was not long enough to observe an increase of the Nitrospira population.

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Competition between nitrospira spp. and nitrobacter spp. in nitrite-oxidizing bioreactors

In situ microbial fuel cell-based biosensor for organic carbon

Environmental issues are a critical factor for the today industry competitiveness. Indeed, the society and the individual consumers could set a common framework for companies’ commitment and engagement regarding environment protection. Redesign the process, recover by-products or reuse effluents are some of the possible actions towards an eco-efficient strategy. Nevertheless, a point remains crucial in such mission: the ability to defend natural ecosystems from polluted wastewaters. For such purpose, a wastewater treatment plant that maximizes removal efficiency and minimizes investment and operation costs is a key factor. Brewery and winery are traditional industries with an important economic value in the agro-food sector. In 2003, the total beer production in the European Union (18 countries) was 344 x 10 m, being recorded around 1800 breweries with 110 thousand employees. If Norway, Switzerland and Turkey are also included, those numbers rise up to 358 x 10 m, 1839 units and 117 thousand, respectively. The excise revenue from beer industry in all these countries reaches over 8800 x 10 € (The Brewers of Europe, 2004). The worldwide wine production is 261 x 10 m (data from 2002), of which 69 % from Europe, 18 % from America, 5 % from Asia, 4 % from Africa and 4 % from Oceania. The worldwide wine consumption (2002) is 228 x 10 m, distributed by Europe (68 %), America (20 %), Asia (7 %), Africa (3 %) and Oceania (2 %) (OIV, 2002). This chapter intends to present some key points on design and operation in wastewater treatment of brewery and winery industries. Therefore, an introduction of the industrial processes is first presented and then wastewater characteristics and treatment processes are discussed. Finally, the experience of a collaborative effort between

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Regina Nogueira

Papers

Quantification of humic acids in surface water: effects of divalent cations, pH, and filtration.

Phosphorus fractionation in volcanic lake sediments (Azores - Portugal).

Competition between nitrospira spp. and nitrobacter spp. in nitrite-oxidizing bioreactors

In situ microbial fuel cell-based biosensor for organic carbon

Brewery and winery wastewater treatment : some focal points of design and operation