Elsevier

Biosensors and Bioelectronics

Volume 25, Issue 7, 15 March 2010, Pages 1705-1709
Biosensors and Bioelectronics

An innovative reactor-type biosensor for BOD rapid measurement

https://doi.org/10.1016/j.bios.2009.12.018Get rights and content

Abstract

Biochemical oxygen demand (BOD) is one of the most important and widely used parameters for characterizing the organic pollution of water and wastewater. In this paper, a novel reactor-type biosensor for rapid measurement of BOD was developed, based on using immobilized microbial cell (IMC) beads as recognition bio-element in a completely mixed reactor which was used as determining chamber, replacing the traditionally used membrane as recognition bio-element. The IMC beads were freely suspended in the aqueous solution, so the mass transfer resistance for dissolved oxygen and organic compounds significantly reduced, and the quantity of the microbial cells used as recognition element can be easily adjusted, in comparison with the traditional membrane-type BOD biosensor, in which exists a unadjustable contradiction between the quantity of biomass and the thickness of the bio-membrane, thus limiting the stability and the detection limit. This novel kind of BOD biosensor significantly increased the sensitivity of the response, the detecting precision and prolonged the life time of the recognition element. The experimental data showed that the most appropriate temperature for biochemical reaction in the reactor was 30 °C, and the IMC beads could keep the bioactivity for about 70 d at the detecting frequency of 8 times every day. The standard deviation of repeatability and the reproducibility of responses were within ±6.4% and ±5.0%, respectively, which are within acceptable bias limits, and meet the requirement of BOD rapid measurement.

Introduction

Biochemical oxygen demand (BOD) is one of the most important and widely used parameters for characterizing the organic pollution of water and wastewater, which is estimated by determining the amount of oxygen required by aerobic microorganisms for degrading organic matters in wastewater. The BOD value represents the amount of biodegradable organic compounds. The standard method for measuring biodegradable organic levels in wastewater is the 5-day biochemical oxygen demand assay (BOD5) described by the APHA (1998). The BOD test has its widest application in measuring wastes loadings to treatment plants and in evaluating the BOD removal efficiency of such treatment systems (APHA, 1998). The BOD value has been determined conventionally by taking a sample of water, aerating it well, placing it in a sealed bottle, incubating for a standard period of time at 20 ± 1 °C in the dark, and determining the oxygen consumption in the water at the end of incubation. Usually the incubation time is 5 days and BOD values based on this standard are called BOD5 value.

However, the conventional BOD method requires not only 5 days, but also experiences and skills. Therefore, the method using a sensor is a very attractive alternative because it can conduct a measurement within several minutes. Different kinds of BOD sensors for rapid measurement of BOD have been developed in last three decades. Hudson et al. (2008) investigated the possibility of using fluorescence spectrometry as a surrogate for BOD test in water quality assessment. Seo et al. (2009) developed a flow injection analysis system with encapsulated high-density Saccharomyces cerevisiae cells for rapid determination of BOD. Nakamura et al. developed a series of new methods for BOD measurement, including a chemiluminescence BOD measuring method, a spectrophotometric BOD determination method using 2,6-dichlorophenolindophenol as the redox color indicator and the eukaryote S. cerevisiae, a double-mediator system by ferricyanide and menadione using the eukaryote S. cerevisiae, and a absorption-based highly sensitive and reproducible biochemical oxygen demand measurement method for seawater using salt-tolerant yeast S. cerevisiae ARIF KD-003 (Nakamura et al., 2007a, Nakamura et al., 2007b, Nakamura et al., 2007c, Nakamura et al., 2008).

BOD biosensor generally consist of a bio-membrane (containing biological recognition element) and an oxygen electrode (transducer), it can offer the possibility of faster estimation of a BOD5-related parameter. The bio-membrane contains an immobilized bioactive material to catalyze the biochemical reaction. The change in the response of the oxygen electrode is measured in terms of electric current. Karube et al. (1977) reported the first BOD sensor based on the principle of biosensor. Since then, BOD biosensor has been developed in last three decades (Liu et al., 2004a, Liu et al., 2004b, Chen et al., 2008a, Chen et al., 2008b, Kara et al., 2009). However, all these BOD biosensors developed were membrane-type, i.e., they tended to immobilize the microbial cells in a porous membrane such as nitrate cellulose, acetate cellulose membrane and the like. This membrane-type BOD biosensor has several disadvantages, such as (1) due to the utilization of the microbial membrane in the sensor, during the process of the organic compounds and dissolved oxygen permeating the microbial membrane, there exists certain mass transfer resistance, which will result in the decline of dissolved oxygen (DO) to great extent; (2) the biosensor is not stable and the reproducibility of the measurement results is low because of the small amount of biomass immobilized in membrane; (3) the requirement for DO electrode is high due to the decline of DO through membrane, the DO after permeating the membrane declined remarkably, which requires high sensitive oxygen electrode, even though it leads to the inaccuracy of the measuring results.

In recent year, our research group has been carrying on the study on the rapid measurement of BOD using a novel BOD sensor, based on the completely mixed determining chamber containing immobilized microbial cell (IMC) beads instead of bio-membrane element used in conventional BOD sensor. The reactor-type BOD biosensor invented by our group can overcome the drawbacks of the membrane-type BOD biosensor (Wang, 2002, Wang et al., 2003a, Wang et al., 2003b, Ye et al., 2005, Chen et al., 2007).

Entrapment of cells in polymeric matrixes is widely used for cell immobilization. Many natural and synthetic polymers have been used. Polyvinyl alcohol (PVA) is a promising type of synthetic polymer, which is cheap and nontoxic to microorganisms. It is very suitable for microbial immobilization (Wang et al., 1995).

We fabricated the recognition component by using polyvinyl alcohol (PVA) to immobilize the microbial cells, which forms small-size microbial spherical particles. The PVA gel has large specific area, porous surface, and the particles suspended in the aqueous solution dispersedly, so the mass transfer resistance for dissolved oxygen and organic compounds was much smaller, compared with the traditional membrane-type BOD sensor. Therefore, this kind of biosensor could enhance the accuracy of the measuring results. On the other hand, it could also shorten the measuring time because the quantity of the microbial cells was much higher than that of membrane-type BOD sensor.

The objective of this study was to investigate the response characteristics of the novel BOD biosensor, including the effect of temperature, the life time of IMC beads, and the repeatability and the reproducibility of the sensor BOD measurements.

Section snippets

Chemicals

PVA (polyvinyl alcohol), calcium chloride, glucose and glutamic acid were purchased from Beijing Chemical Reagents Company. Other reagents were commercially available analytical reagents of laboratory grade materials.

Microorganisms

Activated sludge was collected from Beijing Gaobeidian Sewage Treatment Plant and cultivated under aerobic conditions at 30 °C. The growth medium consisted of CaCl2·2H2O, 1 mg; MgSO4·7H2O, 19 mg; K2HPO4, 4.4 mg; NH4HCO3, 26.8 mg; C6H12O6, 0.1031 g. The pH of the medium was maintained at

Effect of temperature

Considering that the appropriate temperature for activated sludge from sewage treatment plant is about 20–30 °C, the temperature effect was examined by calibrating the sensor at 20, 25, 27, and 30 °C, using GGA solution.

The effect of temperature on the sensor response was shown in Fig. 2.

It can be seen that the temperature effect was consistent with the results reported by other researchers (Chee et al., 1999a, Chee et al., 1999b, Chee et al., 2000, Liu et al., 2000, Kim and Park, 2001, Kwok et

Conclusions

The novel reactor-type BOD biosensor was more effective for BOD measurement, in which IMC beads were used as recognition element for detecting biodegradable organic compounds in samples. The IMC beads suspended in the reactor could decrease the mass transfer resistance for dissolved oxygen and organic compounds, which significantly increased the sensitivity of the sensor response and the detecting precision, it also prolonged the life time of the recognition element to about 70 d. The standard

Acknowledgements

This work was supported by the High-Tech Program (863) of China (Grant No. 2007AA06A404) and Key Industralization Project of Jiangsu Province (Grant No. BA2009100).

References (31)

  • G.J. Chee et al.

    Anal. Chim. Acta

    (1999)
  • G.J. Chee et al.

    Anal. Chim. Acta

    (1999)
  • G.J. Chee et al.

    Biosens. Bioelectron.

    (2000)
  • H. Chen et al.

    Anal. Chim. Acta

    (2008)
  • N. Hudson et al.

    Sci. Total Environ.

    (2008)
  • J.B. Jia et al.

    Biosens. Bioelectron.

    (2003)
  • M.N. Kim et al.

    Sens. Actuators B: Chem.

    (2001)
  • N.Y. Kwok et al.

    Sens. Actuators B: Chem.

    (2005)
  • F. Li et al.

    Biosens. Bioelectron.

    (1994)
  • J. Liu et al.

    Biosens. Bioelectron.

    (2000)
  • J. Liu et al.

    Biosens. Bioelectron.

    (2004)
  • J. Liu et al.

    Biosens. Bioelectron.

    (2004)
  • H. Nakamura et al.

    Anal. Chim. Acta.

    (2007)
  • H. Nakamura et al.

    Anal. Biochem.

    (2007)
  • H. Nakamura et al.

    Talanta

    (2007)
  • Cited by (0)

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