title: MICREDOX--development of a ferricyanide-mediated rapid biochemical oxygen demand method using an immobilised Proteus vulgaris biocomponent.
abstract: 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, 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 Lentikat disks, were incubated with an excess of redox mediator (potassium hexacyanoferrate(III)) and organic substrate for 1h at 37 degrees C 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 BOD5 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 l(-1) glucose, 150 mg l(-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 1h, 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 P. vulgaris were typically 60% for free cells and 35-50% for immobilised cells.
authors.affiliation: Lincoln Technology, Lincoln Ventures Ltd., P.O. Box 133, Lincoln, Christchurch 8152, New Zealand. pascon@lincoln.ac.nz
authors.forename: Neil
authors.initials: N
authors.lastname: Pasco
authors.forename: Keith
authors.initials: K
authors.lastname: Baronian
authors.forename: Cy
authors.initials: C
authors.lastname: Jeffries
authors.forename: Judith
authors.initials: J
authors.lastname: Webber
authors.forename: Joanne
authors.initials: J
authors.lastname: Hay
mesh_terms: D015374:Biosensing Techniques / Q000295:instrumentation / Q000379:methods*; D018914:Cells, Immobilized / Q000187:drug effects / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D005292:Ferricyanides / Q000378:metabolism* / Q000494:pharmacology*; D009930:Organic Chemicals / Q000032:analysis / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000032:analysis / Q000378:metabolism*; D010101:Oxygen Consumption / Q000502:physiology*; D011514:Proteus vulgaris / Q000187:drug effects* / Q000302:isolation & purification / Q000378:metabolism; D014873:Water Pollutants / Q000032:analysis* / Q000378:metabolism
chemical_list: D005292:Ferricyanides; D009930:Organic Chemicals; D014873:Water Pollutants; D010100:Oxygen; C028033:potassium ferricyanide