Biochemical mediator demand - a novel rapid alternative for measuring biochemical oxygen demand

The biochemical oxygen demand (BOD) test (BOD5) is a crucial environmental index for monitoring organic pollutants in waste water but is limited by th e 5-day requirement for completing the test. We have optimised a rapid micr obial technique for measuring the BOD of a standard BOD5 substrate (150 mg glucose/l, 150 mg glutamic acid/l) by quantifying an equivalent biochemical mediator demand in the absence of oxygen. Elevated concentrations of Esche richia coli were incubated with an excess of redox mediator, potassium hexa cyanoferrate(III), and a known substrate for 1 h at 37 degrees C without ox ygen. The addition of substrate increased the respiratory activity of the m icroorganisms and the accumulation of reduced mediator; the mediator was su bsequently re-oxidised at a working electrode generating a current quantifi able by a coulometric transducer. Catabolic conversion efficiencies exceedi ng 75% were observed for the oxidation of the standard substrate. The inclu sion of a mediator allowed a higher co-substrate concentration compared to oxygen and substantially reduced the incubation time from 5 days to Ih. The technique replicates the traditional BOD5 method, except that a mediator i s substituted for oxygen, and we aim to apply the principle to measure the BOD of real waste streams in future work.