Disposable sensor for biochemical oxygen demand

 Disposable-type microbial sensors were prepared for the determination of biochemical oxygen demand (BOD). The yeast, Trichosporon cutaneum, was directly immobilized on the surface of miniature oxygen electrodes using an ultraviolet crosslinking resin (ENT-3400). The oxygen electrodes (15 mm× 2 mm×0.4 mm) were made on silicon substrates using micromachining techniques. They were Clark-type two-electrode systems with−1021 mV applied to the working electrode. Typical response times of the BOD sensors were in the range of 7–20 min. At 20°C, the sensors’ dynamic range was from 0 to 18 mg/l BOD when a glucose/glutamate BOD standard solution was used. The lower limit of detection was 0.2 mg/l BOD. This value was one order of magnitude lower than that of sensors previously reported. The sensors’ operational lifetime of 3 days was satisfactory for a disposable type. The sensors’ responses were reproducible to within 8% relative standard deviation. The BOD sensors’ were applied to untreated and treated waste waters from industrial effluents and municipal sewage. BOD values determined using these sensors correlated well with those determined by the conventional 5-day BOD determination method. Received: 22 December 1995/Received revision: 19 February 1996/Accepted: 17 March 1996     

Towards an on-line biochemical oxygen demand analyser

A simple, and effective tool to measure BOD with a 98% correlation to theoretical BOD values has been developed using a technique of continuous short term measurements of O₂ consumption rates. Measurement times are in the range of 5 to 10 h depending on the initial BOD, instead of 5 days required in the conventional BOD₅ analysis. A bioreactor containing calcium alginate entrapped activated sludge microorganisms was used with phenol and hydroxybutyric acid (HBA) as model substrates.     

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.     

Mechanism of D-cycloserine action: transport mutants for D-alanine, D-cycloserine, and glycine

The accumulation of d-alanine and the accumulation of glycine in Escherichia coli are related and appear to be separate from the transport of l-alanine. The analysis of four d-cycloserine-resistant mutants provides additional support for this conclusion. The first-step mutant from E. coli K-12 that is resistant to d-cycloserine was characterized by the loss of the high-affinity line segment of the d-alanine-glycine transport system in the Lineweaver-Burk plot. This mutation, which is linked to the met(1) locus, also resulted in the loss of the ability to transport d-cycloserine. The second-step mutation that is located 0.5 min from the first-step mutation resulted in the loss of the low-affinity line segment for the d-alanine-glycine transport system. The transport of l-alanine was decreased only 20 to 30% in each of these mutants. A multistep mutant from E. coli W that is 80-fold resistant to d-cycloserine lost >90% of the transport activity for d-alanine and glycine, whereas 75% of the transport activity for l-alanine was retained. E. coli W could utilize either d- or l-alanine as a carbon source, whereas the multistep mutant could only utilize l-alanine. Thus, a functioning transport system for d-alanine and glycine is required for both d-cycloserine action and growth on d-alanine.     

Effects of dilution on dissolved oxygen depletion and microbial populations in the biochemical oxygen demand determination

The biochemical oxygen demand (BOD) value is still a key parameter that can determine the level of organics, particularly the content of biodegradable organics in water. In this work, the effects of sample dilution, which should be done inevitably to get appropriate dissolved oxygen (DO) depletion, on the measurement of 5-day BOD (BOD₅), was investigated with and without seeding using natural and synthetic water. The dilution effects were also evaluated for water samples taken in different seasons such as summer and winter because water temperature can cause a change in the types of microbial species, thus leading to different oxygen depletion profiles during BOD testing. The predation phenomenon between microbial cells was found to be dependent on the inorganic nutrients and carbon sources, showing a change in cell populations according to cell size after 5-day incubation. The dilution of water samples for BOD determination was linked to changes in the environment for microbial growth such as nutrition. The predation phenomenon between microbial cells was more important with less dilution. BOD₅ increased with the specific amount of inorganic nutrient per microbial mass when the natural water was diluted. When seeding was done for synthetic water samples, the seed volume also affected BOD due to the rate of organic uptake by microbes. BOD₅ increased with the specific bacterial population per organic source supplied at the beginning of BOD measurement. For more accurate BOD measurements, specific guidelines on dilution should be established.     

Mechanism of D-cycloserine action: transport systems for D-alanine, D-cycloserine, L-alanine, and glycine

The accumulation of d-alanine, l-alanine, glycine, and d-cycloserine in Escherichia coli was found to be mediated by at least two transport systems. The systems for d-alanine and glycine are related, and are separate from that involved in the accumulation of l-alanine. d-Cycloserine appears to be primarily transported by the d-alanine-glycine system. The accumulation of d-alanine, glycine, and d-cycloserine was characterized by two line segments in the Lineweaver-Burk analysis, whereas the accumulation of l-alanine was characterized by a single line segment. d-Cycloserine was an effective inhibitor of glycine and d-alanine accumulation, and l-cycloserine was an effective inhibitor of l-alanine transport. The systems were further differentiated by effects of azide, enhancement under various growth conditions, and additional inhibitor studies. Since the primary access of d-cycloserine in E. coli is via the d-alanine-glycine system, glycine might be expected to be a better antagonist of d-cycloserine inhibition than l-alanine. Glycine and d-alanine at 10(-5)m antagonized the effect of d-cycloserine in E. coli, whereas this concentration of l-alanine had no effect.     

A fast estimation of biochemical oxygen demand using microbial sensors

Summary Microbial amperometric sensors for biochemical oxygen demand (BOD) determination using Bacillus subtilis or Trichosporon cutaneum cells immobilized in polyvinylalcohol have been developed. These sensors allow BOD measurements with very short response times (15–30s), a level of precision of ±5% and an operation stability of 30 days. A linear range was obtained for a B. subtilis-based sensor up to 20 mg/l BOD and for a T. cutaneum-based sensor up to 100 mg/l BOD using a glucose/glutamic acid standard.     

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.     

Immobilised activated sludge based biosensor for biochemical oxygen demand measurement

A biochemical oxygen demand (BOD) sensor, based on an immobilised mixed culture of microorganisms in combination with a dissolved oxygen electrode, has been developed for the purpose of on-line monitoring of the biological treatment process for waste and wastewater. The sensor was designed for easy replacement of the biomembrane, thereby making it suitable for short-term use. The drawbacks of activated sludge based sensor, such as short sensor lifetime, were thereby circumvented. The sensor BOD measurements were carried out in the kinetic mode using a flow injection system, resulting in 25 s for one measurement followed by 4–8 min recovery time. Based on the results of normalised sensor responses, the OECD synthetic wastewater was considered to be a more suitable calibration solution in comparison with the GGA solution. Good agreement was achieved between the results of the sensor BOD measurement and those obtained from BOD₅ analysis of a wastewater sample from a food-processing factory. Reproducibility of responses using one sensor was below ±5.6% standard deviation. Reproducibility of responses using different sensors was within acceptable bias limits, viz. ±15% standard deviation.     

Development of photocatalytic biosensor for the evaluation of biochemical oxygen demand

The photocatalytic biosensor of flow system using semiconductor TiO2 was developed to evaluate biochemical oxygen demand (BOD) levels in river water. Photocatalysis of sample was carried out in a photoreactor with TiO2 and a 6W black-light blue fluorescent tube as light source. Sample from a photoreactor outlet was measured by an oxygen electrode with a biofilm. The sensor response of photocatalytic biosensor was between 5 and 10 min depending on concentration of biochemical in the samples. At BOD of 1 mgl-1, the sensor response increased 1.33-fold in comparison with that without photocatalysis. The degradation of tannic acid and humic acid with photocatalysis were 51.8 and 38.4%, respectively. Gum arabic and linear alkylbenzene sulfonate (LAS) were degraded a little, but gave the responses of more than double to the sensor. Free radicals yielded by photocatalysis in a photoreactor did not affect the sensor response because their lifetime is extremely short. Fairly good correlation (r=0.983) between the sensor method and the conventional method was obtained for test samples. This biosensor using photocatalytic pretreatment improved the sensitivity.     

Optical fiber biosensor for the determination of low biochemical oxygen demand

An optical fiber biosensor was developed for the evaluation of low Biochemical Oxygen Demand (BOD) values in river waters. Artificial wastewater (AWW) solution was employed as standards for the calibration of the BOD sensor. The response time of the sensor was 15 min, and the optimal BOD response was observed at 30 degrees C, pH 7.0. A linear relationship was obtained between the output voltage and BOD5 values, and the range of determination was 1-10 mg l(-1) BOD. The sensor response was almost not influenced by chloride ion up to 1000 mg l(-1), and also not affected by heavy metal ions (Fe3+, Cu2+, Mn2+, Cr3+, Zn2+). The BOD of river waters was estimated by using the optical fiber biosensor, and good correlation between the sensor and BOD5 test was obtained (r2 = 0.971).     

Characterisation of organic fractions of pulp and paper mill wastewater with a manometric respirometric biochemical oxygen demand method and automatic chemical oxygen demand analyses

Abstract

The manometric respirometric method was applied to a characterisation of organic material in pulp and paper mill wastewater, which is usually high in organic content and inhibitory substances. Preliminary tests, including experiments with an extra microbial seed as well as dilution series, were carried out before the characterisation analyses in order to optimise the method. Three different physical-chemical methods were then used to characterise organic fractions. Influent organic fractions were specified with two methods in which the determination of the soluble biodegradable and the soluble inert fraction differed. In the third method, the influent fractions as well as the new metabolic products generated during the biodegradation process and an estimate of the mineralised part of the influent biodegradable fraction were determined without any hypothetical conversion factors. The results showed that a remarkable part of the detected oxygen demand was consumed for the biotransformation of biodegradable fractions into new inert organic products, not only for mineralisation. The amount of these new metabolic products, measured after biochemical oxygen demand analyses, was significant. It was also noticed that volatile organic compounds can have an influence on the chemical oxygen demand value of effluents.     

Continuous determination of biochemical oxygen demand using microbial fuel cell type biosensor

A mediator-less microbial fuel cell (MFC) was used as a biochemical oxygen demand (BOD) sensor in an amperometric mode for real-time wastewater monitoring. At a hydraulic retention time of 1.05 h, BOD values of up to 100 mg/l were measured based on a linear relationship, while higher BOD values were measured using a lower feeding rate. About 60 min was required to reach a new steady-state current after the MFCs had been fed with different strength artificial wastewaters (Aws). The current generated from the MFCs fed with AW with a BOD of 100 mg/l was compared to determine the repeatability, and the difference was less than 10%. When the MFC was starved, the original current value was regained with a varying recovery time depending on the length of the starvation. During starvation, the MFC generated a background level current, probably due to an endogenous metabolism.     

Influence of batch-specific biochemical egg characteristics on embryogenesis and hatching success in farmed pikeperch

Low and variable egg quality remains a major issue in aquaculture impeding a reliable and continuous supply of larvae, particularly in emerging species, such as pikeperch, Sander lucioperca. We assessed the influence of batch-specific egg parameters (fatty acid (FA) profiles, cortisol content) on embryo life-stages until hatching (survival at 2, 24, 48, 72 h post fertilization (hpf), hatching rate) in an integrated study under commercial hatchery conditions (44 egg batches). Embryo mortality was elevated until 48 hpf (average 9.8% mortality between 2 and 48 hpf). Embryos surviving until 48 hpf were very likely (98.5%) to hatch successfully. The inherent egg FA composition was variable in-between batches. Total FA content ranged form 66.1 to 171.7 µg/mg (dry matter) total FA. Whereas specific FA,18 : 0 and 20 : 5(n-3) (eicosapentaenoic acid) of the polar fraction and the ratio of 22 : 6(n-3) (docosahexaenoic acid) to 20 : 5(n-3) within the neutral fraction, were significantly correlated with early embryo development, contents of the respective FA did not differ between high (>90% hatching rate), mid (70% to 90% hatching rate) and low (<70% hatching rate) quality egg batches. Late embryo development and hatching were relatively independent of the FA profiles highlighting stage-dependent influences especially during early embryogenesis. Cortisol levels ranged from 22.7 to 293.2 ng/ml and did not directly explain for mortalities. However, high cortisol was associated with a lower content of specific FA, in particular highly unsaturated FA. These results demonstrate the magnitude of inter-individual differences in the batch-specific biochemical egg composition under stable hatchery conditions and suggest a stress-mediated lack of essential FA, which in turn affects early embryo survival. Surprisingly, embryos are able to cope well with a broad range of inherent egg parameters, which limits their predictive potential for egg quality in general. Still, specific FA profiles of high quality egg batches have potential for formulating species-specific broodstock diets and improving reproductive management in pikeperch.