Assessing the effect of oxygen and microbial inhibitors to optimize ferricyanide-mediated BOD assay

Microbial Biosensors for Rapid Determination of Biochemical Oxygen Demand: Approaches, Tendencies and Development Prospects

One of the main indices of the quality of water is the biochemical oxygen demand (BOD). A little over 40 years have passed since the practical application of the first microbial sensor for the determination of BOD, presented by the Japanese professor Isao Karube. This time span has brought new knowledge to and practical developments in the use of a wide range of microbial cells based on BOD biosensors. At present, this field of biotechnology is becoming an independent discipline. The traditional BOD analysis (BOD₅) has not changed over many years; it takes no less than 5 days to carry out. Microbial biosensors can be used as an alternative technique for assessing the BOD attract attention because they can reduce hundredfold the time required to measure it. The review examines the experience of the creation and practical application of BOD biosensors accumulated by the international community. Special attention is paid to the use of multiple cell immobilization methods, signal registration techniques, mediators and cell consortia contained in the bioreceptor. We consider the use of nanomaterials in the modification of analytical devices developed for BOD evaluation and discuss the prospects of developing new practically important biosensor models.

Quantifying biodegradable organic matter in polluted water on the basis of coulombic yield

Biodegradable organic matter (BOM) in polluted water plays a key role in various biological purification technologies. The five-day biochemical oxygen demand (BOD₅) index is often used to determine the amount of BOM. However, standard BOD₅ assays, centering on dissolved oxygen detection, have long testing times and often show severe deviation (error ≥ 15%). In the present study, the coulombic yield (Q) of a bio-electrochemical degradation process was determined, and a new index for BOM quantification was proposed. The Q value represents the quantity of transferred electrons from BOM to oxygen, and the corresponding index was defined as BOM_Q. By revealing Q-BOM stoichiometric relationship, we were able to perform a BOM_Q assay in a microbial fuel cell involved technical platform. Experimental results verified that 5-500mgL^-1 of BOM_Q toward artificial wastewater samples could be directly obtained without calibration in several to dozens of hours, leaving less than 5% error. Moreover, the BOM_Q assay remained accurate and precise in a wide range of optimized operational conditions. A ratio of approximately 1.0 between the values of BOM_Q and BOD₅ toward artificial and real wastewater samples was observed. The rapidity, accuracy, and precision of the measurement results are supported by a solid theoretical foundation. Thus, BOM_Q is a promising water quality index for quantifying BOM in polluted water.

Hexacyanoferrate-adapted biofilm enables the development of a microbial fuel cell biosensor to detect trace levels of assimilable organic carbon (AOC) in oxygenated seawater

A marine microbial fuel cell (MFC) type biosensor was developed for the detection of assimilable organic carbon (AOC) in ocean water for the purpose of online water quality monitoring for seawater desalination plants prone to biofouling of reverse osmosis (RO) membranes. The anodophilic biofilm that developed on the graphite tissue anode could detect acetate as the model AOC to concentrations as low as 5 µM (120 µg/L of AOC), which is sufficiently sensitive as an online biofouling risk sensor. Although the sensor was operated at a higher (+200 ± 10 mV) than the usual (-300 mV) anodic potential, the presence of oxygen completely suppressed the electrical signal. In order to overcome this outcompeting effect of oxygen over the anode as electron acceptor by the bacteria, hexacyanoferrate (HCF(III)) was found to enable the development of an adapted biofilm that transferred electrons to HCF(III) rather than oxygen. As the resultant of the reduced HCF(II) could readily transfer electrons to the anode while being re-oxidised to HCF(III), the marine MFC biosensor developed could be demonstrated to work in the presence of oxygen unlike traditional MFC. The possibility of operating the marine MFC in batch or continuous (in-line) mode has been explored by using coulombic or potentiometric interpretation of the signal.

Analytical applications of microbial fuel cells. Part I: Biochemical oxygen demand

Microbial fuel cells (MFCs) are bio-electrochemical devices, where usually the anode (but sometimes the cathode, or both) contains microorganisms able to generate and sustain an electrochemical gradient which is used typically to generate electrical power. In the more studied set-up, the anode contains heterotrophic bacteria in anaerobic conditions, capable to oxidize organic molecules releasing protons and electrons, as well as other by-products. Released protons could reach the cathode (through a membrane or not) whereas electrons travel across an external circuit originating an easily measurable direct current flow. MFCs have been proposed fundamentally as electric power producing devices or more recently as hydrogen producing devices. Here we will review the still incipient development of analytical uses of MFCs or related devices or set-ups, in the light of a non-restrictive MFC definition, as promising tools to asset water quality or other measurable parameters. An introduction to biological based analytical methods, including bioassays and biosensors, as well as MFCs design and operating principles, will also be included. Besides, the use of MFCs as biochemical oxygen demand sensors (perhaps the main analytical application of MFCs) is discussed. In a companion review (Part 2), other new analytical applications are reviewed used for toxicity sensors, metabolic sensors, life detectors, and other proposed applications.