The use of two commercial microbial inocula (Bi-Chem and Biolen M112) as reference organisms for the 5-day biochemical oxygen demand (BOD5) test was studied using both dilution and manometric methods with the standard glucose-glutamic acid solution. A comparative study was carried out performing this test for several real effluent samples with the two commercial inocula and with a treatment plant inoculum. The microbiological characterization of these inocula was performed with the API identification system (bioMerieux S.A., France). The results obtained for the BOD5 of the standard solution are within the range for activated sludge as found in the standards of the cited methods (mean values obtained were BOD5 = 199.4 mg/L O-2 [variation coefficient, VC = 4.52%] and BOD5 = 176.8 mg/L O-2 [VC = 4.66%] for the Bi-Chem inoculum and BOD5 = 209.8 mg/L O-2 [VC = 7.35%] and BOD5 = 228.6 mg/L O-2 [VC = 9.37%] for the Biolen M112 inoculum, with the dilution and manometric methods, respectively). Moreover, Pearson rank correlation analysis for the real effluent samples indicates that correlations between the BOD5 values for the two commercial inocula and for the treatment plant inoculum were highly significant to 95% confidence (r(2) = 0.922 to 1.00. p < 0.05).
