Conventional Biochemical Oxygen Demand Research Articles

Real-time biomonitoring of oxygen uptake rate and biochemical oxygen demand using a novel optical biogas respirometric system

In response to the ever-increasing need for monitoring-based process control of wastewater treatment plants, an online applicable respirometer shows great promise for real-time measurement of oxygen uptake rate (OUR) and biochemical oxygen demand (BOD) measurements as a surrogate of the biodegradability of wastewater. Here, we have developed a photosensor-assisted real-time respirometric system equipped with bubble counting sensors for accurate measurement of microbial oxygen consumption in a bottle. This system can measure OUR and BOD in a bottle equipped with a tube containing NaOH solution to absorb carbon dioxide and supplied with continuous atmospheric oxygen to the bottle, which reliably supplies non-limiting dissolved oxygen (DO) for aerobic biodegradation even at high organic loads. These technical improvements allow a sensitive and rapid analytical tool offering real-time profiles of oxygen uptake rate as well as BOD measurements with an extended measurable range (0–420 mg O2/L), enabling significant reduction or elimination of dilution steps. The respirometric system was used to elucidate the biodegradable kinetics of domestic and swine wastewaters as a function of the type and concentration of organic matters, depending on source characteristics including rapidly or slowly oxidizable organic substances by bacteria. Compared with conventional and manometric BOD methods, our method is reliable and accurate.

Bod sensor for wastewater analysis- design and calibration methods

Water quality monitoring is an important aspect of water management concerning to thepollution control. The removal of biodegradable organic substances is a very importantaspect of evaluation the treatment efficiency in a wastewater treatment plant (WWTP).The amount of oxygen consumed by microorganisms to oxidise organic substances ischaracterised by biochemical oxygen demand (BOD), a widely used parameter inenvironmental analysis. The conventional method BOD determination is uneffective fromthe point of view of short-term in situ measurements or on-line monitoring because itmeasures the microorganisms endogenous and exogenous oxygen consumption over aperiod of 5 or 7 days. BOD biosensors provide much faster results thereby allowing theresearches to overcome the weaknesses of the conventional method.BOD sensor studied in present work is based on an amperometric oxygen sensor and aneasily replaceable biomembrane of mixed culture of microorganisms. Biosensor outputsignal depends on the concentration of substrate that indicates the organic pollution ofwaters. Biosensor output signal is analysed classically according to the steady-stateparameters and by the dynamic change of the response and also by the elaboratedmathematical model. The calibration of biosensor by steady-state method is based on thechange of biosensor response between an initial value and the stable end-point of thesignal. The dynamic method of measurement is based on the determination of themaximum rate of change of output signal during experiment and the mathematical modelenables us to find the time constants characterising the non-steady-state processes inBOD sensor. Studied biosensor can be used for the measurements of biochemical oxygendemand in the concentration range 10-90 mg/L.

Effects of Operating Parameters on Measurements of Biochemical Oxygen Demand Using a Mediatorless Microbial Fuel Cell Biosensor.

The conventional Biochemical Oxygen Demand (BOD) method takes five days to analyze samples. A microbial fuel cell (MFC) may be an alternate tool for rapid BOD determination in water. However, a MFC biosensor for continuous BOD measurements of water samples is still unavailable. In this study, a MFC biosensor inoculated with known mixed cultures was used to determine the BOD concentration. Effects of important parameters on establishing a calibration curve between the BOD concentration and output signal from the MFC were evaluated. The results indicate monosaccharides were good fuel, and methionine, phenylalanine, and ethanol were poor fuels for electricity generation by the MFC. Ions in the influent did not significantly affect the MFC performance. CN− in the influent could alleviate the effect of antagonistic electron acceptors on the MFC performance. The regression equation for BOD concentration and current density of the biosensor was y = 0.0145x + 0.3317. It was adopted to measure accurately and continuously the BOD concentration in actual water samples at an acceptable error margin. These results clearly show the developed MFC biosensor has great potential as an alternative BOD sensing device for online measurements of wastewater BOD.

A simple cost-effective manometric respirometer: design and application in wastewater biomonitoring

Application of respirometric tools in wastewater engineering fields is still not getting familiarity and acceptance by academy or industry in developing countries as compared to the use of conventional biochemical oxygen demand (BOD) approach. To justify the applicability of respirometry, a low-cost respirometric device suitable for monitoring biodegradation process in wastewater has been developed. This device contains six independently operating reactors placed in a temperature control unit for the bioassay of five wastewater samples simultaneously (along with one blank). Each reactor is equipped with a magnetic stirrer for the continuous agitation of the test sample. Six manometers, linked with the individual reactors, measure the pressure and volume changes in the headspace gas phase of the reactor. Working formulae have been derived to convert the ‘volume-change in gas phase’ data to ‘the oxygen depletion in the whole liquid–gas system’ data. The performance of the device has been tested with glucose–glutamic acid standard solution and found satisfactory. Conventional BOD test and the respirometric measurements were performed simultaneously and it is found that in addition to measuring the BOD of the sample, this device gives oxygen uptake profile for further analysis to determine the biokinetic coefficients. Additionally, in some cases, following a specific test protocol, the respirometer can indirectly estimate the carbon dioxide evolved during biodegradation process for calculating respiratory activity parameter such as respiratory quotient. It is concluded that the device can be used in the laboratories associated with the activated sludge plants and also for teaching and research purposes in developing countries.

Restructuring BOD : COD Ratio of Dairy Milk Industrial Wastewaters in BOD Analysis by Formulating a Specific Microbial Seed

BOD (Biochemical oxygen demand) is the pollution index of any water sample. One of the main factors influencing the estimation of BOD is the nature of microorganisms used as seeding material. In order to meet the variation in wastewater characteristics, one has to be specific in choosing the biological component that is the seeding material. The present study deals with the estimation of BOD of dairy wastewater using a specific microbial consortium and compares of the results with seeding material (BODSEED). Bacterial strains were isolated from 5 different sources and were screened by the conventional BOD method. The selected microbial seed comprises of Enterobacter sp., Pseudomonas sp. BOD : COD (Chemical oxygen demand) ratio using the formulated seed comes in the range of 0.7-0.8 whereas that using BODSEED comes in the ratio of 0.5-0.6. The ultimate BOD (UBOD) was also performed by exceeding the 3-day dilution BOD test. After 90 days, it has been observed that the ratio of BOD : COD increased in case of selected consortium 7 up to 0.91 in comparison to 0.74 by BODSEED. The results were analyzed statistically by t-test and it was observed that selected consortium was more significant than the BODSEED.

THE DEVELOPMENT OF BIOCHEMICAL OXYGEN DEMAND SENSOR USING LOCAL YEAST: Candida fukuyamaensis, UICC Y-247

In order to shorten the measurement time of biochemical oxygen demand (BOD), a BOD sensor based on yeast metabolism was developed. Local yeast, Indonesian Origin, Candida fukuyamaensis UICC Y-247, was used as a transducer. The yeast was immobilized as a thin film in agarose matrix with the auxiliary of Nafion® acting as the membrane for ion exchange process. The film was then attached to gold-modified glassy carbons and used as transducer on the working electrodes. The measurements were conducted by observing the depletion of glucose concentration using multipulse amperometric method and then converted to BOD values. Optimum condition was observed in a waiting measurement time of 30 min at an applied potential of 450 mV (vs. Ag/AgCl). Linearity was shown in glucose concentration range of 0.1–0.5 mM, which was equivalent to BOD concentration range of 10–50 mg/L. A detection limit of 1.13 mg/L BOD could be achieved. Good repeatability was shown by a relative standard deviation (RSD) of 2.7% (n = 15). However, decreasing current response of ~50% was found after 3 days. Comparing to the conventional BOD measurement, this BOD sensor can be used as an alternative method for BOD measurements. Keywords: amperometr, BOD sensor, Candida fukuyamaensis UICC Y-247, gold-modified carbon, Indonesian yeast

Application of an Acclimated Microbial Consortium as Biocatalyst for Rapid Determination of Biochemical Oxygen Demand

Biochemical Oxygen Demand (BOD) is an important parameter for water pollution monitoring. Since the conventional BOD assay by American Public Health Association (APHA) takes 5 days to complete (termed BOD5), development of an alternative method that can rapidly measure the amount of biodegradable organics in wastewater is highly desirable. In the present study, single and mixed microbial cultures isolated from different environments in Malaysia were tested as potential biocatalyst in an assay called Ferricyanide Mediated-Biochemical Oxygen Demand (FM-BOD) used for rapid BOD detection. Unlike the BOD5 assay, the FM-BOD is based on biochemical degradation of organic compounds via reduction of ferricyanide as an alternative terminal electron acceptor to dissolved oxygen. The increase in concentration of microbially produced ferrocyanide during incubation of the microorganisms in the presence of ferricyanide and organic substrates was measured voltammetrically using a 10 µm platinum working electrode. Measurements were conducted using linear sweep voltammetry at potential 0-600 mV versus Ag/AgCl reference electrode. Limiting currents were determined by voltammetry at Eapp = +450 mV (vs Ag/AgCl). The amount of ferrocyanide produced was found to be proportional to the amount of biodegradable organics. From the study, it is shown that mixed microbial consortium acted as a better biocatalyst for rapid BOD detection compared to both single cultures and a commercial consortium. The microbial consortium consists of four species of microorganisms. FM-BOD assays were conducted in optimized conditions with microbial consortium at final absorbance of OD600 2.5 and ferricyanide at concentration 60 mM. Results showed that the FM-BOD assay was able to detect biodegradable organics in 1 h compared to the current BOD5 assay of 5 days. This FM-BOD assay with optimized conditions is applicable to food wastewater consisting of easily degradable carbon source.

Appraising bacterial strains for rapid BOD sensing—an empirical test to identify bacterial strains capable of reliably predicting real effluent BODs

The measured response of rapid biochemical oxygen demand (BOD) biosensors is often not identical to those measured using the conventional 5-day BOD assay. This paper highlights the efficacy of using both glucose-glutamic acid (GGA) and Organisation for Economic Cooperation and Development (OECD) BOD standards as a rapid screen for microorganisms most likely to reliably predict real effluent BODs when used in rapid BOD devices. Using these two synthetic BOD standards, a microorganism was identified that produced comparable BOD response profiles for two assays, the MICREDOX® assay and the conventional 5-day BOD(5) test. A factorial experimental design systematically evaluated the impact of four factors (microbial strain, growth media composition, media strength, and microbial growth phase) on the BOD response profiles using GGA and OECD synthetic standard substrates. An outlier was identified that showed an improved correlation between the MICREDOX® BOD (BOD(sens)) and BOD(5) assays for both the synthetic standards and for real wastewater samples. Microbial strain was the dominant factor influencing BOD(sens) values, with Arthrobacter globiformis single cultures clearly demonstrating superior rapid BOD(sens) response profiles for both synthetic and real waste samples. It was the only microorganism to approach the BOD(5) response for the OECD substrate (171 mg O(2)L(-1)), and also reported BOD values for real waste samples that were comparable to those produced by the BOD(5) test, including discriminating between filtered and unfiltered samples.

Immobilized multi-species based biosensor for rapid biochemical oxygen demand measurement

To improve the practicability of rapid biochemical oxygen demand (BOD) method, we proposed a stable BOD sensor based on immobilizing multi-species BODseed for wastewater monitoring in the flow system. The activation time of the biofilm was greatly shortened for the biofilm prepared by BODseed in the organic–inorganic hybrid material. Some influence factors such as temperature, pH, and concentration of phosphate buffer solution (PBS) were investigated in detail in which high tolerance to environment was validated for the BOD sensor permitted a wide pH and PBS concentration ranges. The minimum detectable BOD was around 0.5 mg/l BOD under the optimized 1.0 mg/ml BODseed immobilized concentration. The as-prepared BOD sensor exhibited excellent stability and reproducibility for different samples. Furthermore, the as-prepared BOD biosensor displayed a notable advantage in indiscriminate biodegradation to different organic compounds and their mixture, similar to the character of conventional BOD 5 results. The results of the BOD sensor method are well agreed with those obtained from conventional BOD 5 method for wastewater samples. The proposed rapid BOD sensor method should be promising in practical application of wastewater monitoring.

A flow injection analysis system with encapsulated high-density Saccharomyces cerevisiae cells for rapid determination of biochemical oxygen demand

The biochemical oxygen demand (BOD) determination was studied using a novel flow injection analysis (FIA) system with encapsulated Saccharomyces cerevisiae cells and an oxygen electrode and was compared with conventional 5-day BOD tests. S. cerevisiae cells were packed in a calcium alginate capsule at a dry cell weight of 250 g/l of capsule core. The level of dissolved oxygen (DO) was reduced due to the enhanced respiratory activity of the microbial cells when the injected nutrient passed through the bioreactor. The decrease in DO (DeltaDO) was intensified with the amount of microbial cells packed in the bioreactor. However, the specific DeltaDO decreased as the amount of cells loaded in the bioreactor increased. The DeltaDO value was dependent on the pH and temperature of the mobile phase and reached its maximum value at 35 degrees C and pH 7-8. Also, DeltaDO became larger at longer response times as the flow rate of the mobile phase decreased. The measurement of DeltaDO was repeated more than six times consecutively using a 20-ppm standard glucose and glutamic acid solution, which confirmed the reproducibility with a standard deviation of 0.95%. A strong linear correlation between DeltaDO and BOD was also observed. The 5-day BOD values of actual water and wastewater samples were in accordance with the BOD values obtained by this FIA method using encapsulated S. cerevisiae cells. Unlike the cell-immobilized bead system, there was no contamination of the bioreactor resulting from any leak of yeast cells from the sensor capsules during BOD measurements.

A New Approach to Characterize Biodegradation of Organics by Molecular Mass Distribution in Landfill Leachate

This study provides biodegradability of organics in leachate according to their molecular mass distributions (<0.5, 0.5 to 1, 1 to 3, 10, and >10 KDa). Organics with molecular mass values lower than 0.5 KDa were the predominant species in the raw leachate filtrate, and the aerated lagoon process was very effective in treating these highly biodegradable organics; the Fenton's oxidation process was very effective in treating not-so-biodegradable organics with molecular mass values higher than 0.5 KDa, but a portion of these organics were converted into organics <0.5 KDa after Fenton's oxidation. An oxygen uptake measurement using a respirometer was more sensitive than a conventional biochemical oxygen demand measurement to evaluate bioactivities, especially when bioactivities were low.

A novel approach based on ferricyanide-mediator immobilized in an ion-exchangeable biosensing film for the determination of biochemical oxygen demand

A novel biochemical oxygen demand (BOD) sensing method employing a ferricyanide (FC) mediator immobilized in an ion-exchangeable polysiloxane was developed. The ion-exchangeable polysiloxane containing alkylammonium groups (PAPS-Cl) was synthesized by sol–gel reaction of 3-(aminopropyl)trimethoxysilane (APTMOS) catalyzed by hydrochloric acid. FC was combined in PAPS-Cl via ion-association and the product was labeled as PAPS-FC, which was employed for a modified glassy carbon electrode. The apparent diffusion coefficient ( D app) of FC on the modified glassy carbon electrode was 9.8 × 10 −11 cm 2 s −1. In a three-electrode system, a linear relationship between the anodic current responses and glucose/glutamate (GGA) concentration was obtained up to 40 mg O 2 L −1 ( r = 0.994) when the reaction mixture was incubated for 30 min. Single sensor and piece-to-piece reproducibility were less than 3.8 and 7.7%, respectively. The effects of dissolved oxygen, pH, temperature and co-existing substances on the BOD responses were studied. The sensor responses to nine pure organic substances were compared with the conventional BOD 5 method and other biosensor methods. Detection results of seawater samples were compared with those obtained from the BOD 5 method and showed a good correlation ( r = 0.988).

A new BOD estimation method employing a double-mediator system by ferricyanide and menadione using the eukaryote Saccharomyces cerevisiae

A new biochemical oxygen demand (BOD) sensing method employing a double-mediator (DM) system coupled with ferricyanide and a lipophilic mediator, menadione and the eukaryote Saccharomyces cerevisiae has been developed. In this study, a stirred micro-batch-type microbial sensor with a 560 μL volume and a two-electrode system was used. The chronamperometric response of this sensor had a linear response between 1 μM and 10 mM hexacyanoferrate(II) ( r 2 = 0.9995, 14 points, n = 3, average of relative standard deviation and R.S.D. av = 1.3%). Next, the optimum conditions for BOD estimation by the DM system (BOD DM) were investigated and the findings revealed that the concentration of ethanol, used to dissolve menadione, influenced the sensor response and a relationship between the sensor output and glucose glutamic acid concentration was obtained over a range of 6.6–220 mg O 2 L −1 (five points, n = 3, R.S.D. av 6.6%) when using a reaction mixture incubated for 15 min. Subsequently, the characterization of this sensor was studied. The sensor responses to 14 pure organic substances were compared with the conventional BOD 5 method and other biosensor methods. Similar results with the BOD biosensor system using Trichosporon cutaneum were obtained. In addition, the influence of chloride ion, artificial seawater and heavy metal ions on the sensor response was investigated. A slight influence of 20.0 g L −1 chloride ion and artificial seawater (18.4 g L −1 Cl −) was observed. Thus, the possibility of BOD determination for seawater was suggested in this study. In addition, no influence of the heavy metal ions (1.0 mg L −1 Fe 3+, Cu 2+, Mn 2+, Cr 3+ and Zn 2+) was observed. Real sample measurements using both river water and seawater were performed and compared with those obtained from the BOD 5 method. Finally, stable responses were obtained for 14 days when the yeast suspension was stored at 4 °C (response reduction, 93%; R.S.D. for 6 testing days, 9.1%).

An optical biosensor for multi-sample determination of biochemical oxygen demand (BOD)

An optical biosensor for parallel multi-sample determination of biochemical oxygen demand (BOD) in wastewater samples has been developed. The biosensor monitors the dissolved oxygen (DO) concentration in water through an oxygen sensing film immobilized on the bottom of glass sample vials. The oxygen sensing film contains the tris(4,7-diphenyl-1,10-phenanthroline) ruthenium(II) dye (Ru(dpp)) the luminescence intensity of which varies with oxygen concentration. A computer-controlled moving optrode head with four blue light emitting diodes (LEDs) was scanned sequentially under each sample vial. The luminescence signal was collected by an optical cable and transmitted to a photomultiplier tube (PMT) and processed by a microcomputer. The microbial samples (activated sludge and Bacillus subtilis were immobilized in a sol–gel composite material of silica and poly(vinyl alcohol)-grafted-poly(vinylpyridine) on the oxygen sensing film. The performance of the microbial film as a function of cell loading, thickness, temperature and pH and in the presence of heavy metals as well as its stability and service life have been investigated. The BOD value was determined from the rate of oxygen consumption by the microorganisms in the first 20 min. The BOD values obtained from this biosensor correlates well with the results of the conventional 5-day BOD test.

A simplified headspace biochemical oxygen demand test protocol based on oxygen measurements using a fiber optic probe.

Batch respirometric tests have many advantages over the conventional biochemical oxygen demand (BOD) method for analysis of wastewaters, including the use of nondiluted samples, a more rapid exertion of oxygen demand, and reduced sample preparation time. The headspace biochemical oxygen demand (HBOD) test can be used to obtain oxygen demands in 2 or 3 days that can predict 5-day biochemical oxygen demand (BOD5) results. The main disadvantage of the HBOD and other respirometric tests has been the lack of a simple and direct method to measure oxygen concentrations in the gas phase. The recent commercial production of a new type of fiber optic oxygen probe, however, provides a method to eliminate this disadvantage. This fiber optic probe, referred to here as the HBOD probe, was tested to see if it could be used in HBOD tests. Gas-phase oxygen measurements made with the HBOD probe took only a few seconds and were not significantly different from those made using a gas chromatograph (t test: n = 15, R2 = 0.9995, p < 0.001). In field tests using the HBOD probe procedure, the probe greatly reduced sample analysis time compared with previous HBOD and BOD protocols and produced more precise results than the BOD test for wastewater samples from two treatment plants (University Area Joint Authority [UAJA] Wastewater Treatment Plant in University Park, Pennsylvania, and The Pennsylvania State University [PSU] Wastewater Treatment Plant in University Park). Headspace biochemical oxygen demand measurements on UAJA primary clarifier effluent were 59.9 +/- 2.4% after 2 days (HBOD2) and 73.0 +/- 3.1% after 3 days (HBOD) of BOD, values, indicating that BOD5 values could be predicted by multiplying HBOD2 values by 1.67 +/- 0.07 or HBOD3 by 1.37 +/- 0.06. Similarly, tests using PSU wastewater samples could be used to provide BOD5 estimates by multiplying the HBOD2 by 1.24 +/- 0.04 or by multiplying the HBOD3 by 0.97 +/- 0.03. These results indicate that the HBOD fiber optic probe can be used to obtain reliable oxygen demands in batch respirometric tests such as the HBOD test.

Co-immobilized microbial biosensor for BOD estimation based on sol–gel derived composite material

A novel type of biochemical oxygen demand (BOD) biosensor was developed for water monitor, based on co-immobilizing of Trichosporon cutaneum and Bacillus subtilis in the sol–gel derived composite material which is composed of silica and the grafting copolymer of poly (vinyl alcohol) and 4-vinylpyridine (PVA-g-P(4-VP)). Factors that influence the performance of the resulting biosensor were examined. The biodegradable substrate spectrum could be expanded by the co-immobilized microorganisms. The biosensor prepared also exhibited good reproducibility and long-term stability. Good agreement was obtained between the results of the sensor BOD measurement and those obtained from conventional BOD 5 method for water samples.

BOD analysis of industrial effluents: 5 days to 5 min

Abstract Wastewater generation and its subsequent treatment is a major problem for every industry and for the society as well. Prior to treatment, the wastewaters need to be monitored so as to permit their discharge into the local water resources. Amongst all the parameters for which the wastewaters are monitored, biochemical oxygen demand (BOD), is one of the most important and frequently used parameters for estimating the level of water pollution. The control of wastewater treatment plants is very difficult or even impossible using the classical determination method for BOD because of its high time consumption (3–5 days). The need for fast, portable and cost-effective methods for environmental monitoring has stimulated the production of a variety of field analytical tools such as biosensors. Biosensors are device that have several unique features such as compact size, simple to use, one step reagentless analysis, low cost and quick-real time results. The conventional BOD measurement requires 3–5 days, which a microbial BOD biosensor senses within minutes. A number of microbial BOD sensors have been developed nationally and internationally. The drawback of such developed sensors is that they cannot be used for all types of industrial and domestic wastewaters. Our developed BOD biosensor is based on a pre-tested, synergistic formulated microbial consortium. It is capable to sense the BOD load of a wide variety of synthetic as well as industrial wastewaters having low–moderate–high biodegradability within minutes. The sensor BOD values show a good linear relationship with the BOD values obtained using the conventional method upto a GGA concentration of 90 mg/l (r=0.938). BOD values of real wastewater samples from different industries viz, distillery dairy and tannery were analysed using the developed sensor. The BOD sensor results were found to be comparable with those obtained using the conventional 3-day method.

Use of biodegradable dissolved organic carbon to assess treatment process performance in relation to solids retention time.

A biodegradable dissolved organic carbon (BDOC) method has been developed and used to analyze secondary- and advanced-treated wastewater effluents and to investigate correlations between residual organic content and the solids retention time (SRT). Conventional biochemical oxygen demand (BOD) bottles and a 28-day incubation period were used. Secondary wastewater effluents from Hawaii were found to contain between 9.0 and 14.0 mg/L of dissolved organic carbon (DOC), of which 23 to 35% was biodegradable in the 28-day BDOC test (from a survey of nine treatment plants). Bench-scale, continuous-flow activated-sludge biological reactors treating synthetic wastewater were operated at SRTs between 2 and 15 days, and effluent BDOCs were determined. A good BDOC prediction equation was developed that incorporates the initial DOC, the DOC remaining after 5 days, and the SRT of the system from which the sample originated. This equation can be used to determine the BDOC value using data that can be obtained during a conventional 5-day BOD test. The determined equation was found to be appropriate for some of the full-scale wastewater effluent survey data.

Improvement of a mediator-type biochemical oxygen demand sensor for on-site measurement

We characterized a mediator-type biochemical oxygen demand (BOD) sensor with a three-electrode system using potassium ferricyanide (FC) and Pseudomonas fluorescens in our previous study. In the present study, we have utilized the advantages of a mediator-type biosensor, which does not require air-supply equipment for on-site measurements, and made a fully disposable sensor tip for a portable device. The tip consists of a two-electrode system with P. fluorescens immobilized on a cellulose acetate membrane and is packaged in polyester film to prevent it from drying out. By aeration with a 0.1 M NaCl solution of P. fluorescens (after growth), the sensor responses as well as their reproducibility and stability have been successfully improved. The responses increased more than seven times, and the calibration curve from 15 to 260 mg l −1 also remained linear although the response decreased approximately half the original after at least 35 days in storage. The reproducibility of the sensor responses improved to 12.7% (average of relative standard deviations (RSDs)) in the calibration curve obtained by using the Organization for Economic Cooperation and Development synthetic sewage. Examination of real samples from three different sources showed that the BOD as determined by the sensor correlates well with the conventional 5-day BOD method ( r 2=0.982, 0.823, and 0.809). Consequently, the aeration process makes it possible to realize rapid, and in situ measurements without the long conditioning process that is generally required to activate the microorganisms immobilized on bio-films before use. Finally, we have designed a portable device that utilizes our disposable sensor tip.

Development of highly sensitive BOD sensor and its evaluation using preozonation

A highly sensitive microbial sensor for biochemical oxygen demand (BOD) is described based on preozonation of refractory organic compounds in river waters. The hydroxyl radical generated by ozone decomposition was used as oxidant to split up organic compounds. Artificial wastewater (AWW) solutions were employed as standard solutions for the calibrations of the BOD sensor. The degree of degradation of organic compounds after ozonation of humic acid, lignin, tannic acid, gum arabic and surfactants were investigated as total organic carbon (TOC) reduction rates. The ozonation of AWW solutions was carried out by 42.4 g N −1 m −3 ozone for 3 min at pH 7.0. TOC reduction rates of humic acid and tannic acid were 22% and 18%, respectively, but gum arabic showed extremely low values. The sensor response to 1 mg l −1 BOD after ozonation was twice than that before ozonation. A typical response time of the BOD sensor was ca. 5 min, and the 3 σ lower detection limit was 0.2 mg l −1 BOD. BOD values estimated by the biosensor correlated well with those determined by the conventional BOD 5 method.