Journal
BIOSENSORS & BIOELECTRONICS
Volume 20, Issue 3, Pages 524-532Publisher
ELSEVIER ADVANCED TECHNOLOGY
DOI: 10.1016/j.bios.2004.02.016
Keywords
biochemical oxygen demand; microbial sensor; BOD5; immobilisation; wastewater; redox mediator
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Biochemical oxygen demand (BOD) is an international regulatory environmental index for monitoring organic pollutants in wastewater and the current legislated standard test for BOD monitoring requires 5 days to complete (BOD5 test). We are developing a rapid microbial technique, MICREDOX(R), for measuring BOD by eliminating oxygen and, instead, quantifying an equivalent biochemical co-substrate demand, the co-substrate being a redox mediator. Elevated concentrations of Proteus vulgaris, either as free cells or immobilised in Lentika(R) disks, were incubated with an excess of redox mediator (potassium hexacyanoferrate(III)) and organic substrate for 1 h at 37degreesC without oxygen. The addition of substrate increased the catabolic activity of the microorganisms and the accumulation of reduced mediator, which was subsequently re-oxidised at a working electrode generating a current quantifiable by a coulometric transducer. The recorded currents were converted to their 130135 equivalent with the only assumption being a fixed conversion of substrate and known stoichiometry. Measurements are reported both for the BOD5 calibration standard solution (150 mg 1(-1) glucose, 150 mg 1(-1) glutamic acid) and for filtered effluent sampled from a wastewater treatment plant. The inclusion of a highly soluble mediator in place of oxygen facilitated a high ferricyanide concentration in the incubation, which in turn permitted increased concentrations of microorganisms to be used. This substantially reduced the incubation time, from 5 days to 1 h, for the biological oxidation of substrates equivalent to those observed using the standard BOD5 test. Stoichiometric conversion efficiencies for the oxidation of the standard substrate by R vulgaris were typically 60% for free cells and 35-50% for immobilised cells. (C) 2004 Elsevier B.V. All rights reserved.
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