Correlation of microbial mass with ATP and DNA concentrations in acidogenesis of whey permeate

In this paper, we examine variations in the contents of ATP and DNA per unit microbial mass in an acidogenesis of whey permeate. We also introduce a novel approach to estimate microbial mass by measuring ATP and DNA when the ratios of ATP and DNA to microbial mass vary. Acidogenic experiments were performed at 35 degrees C and pH 6.0 in batch mode. The amounts of ATP and DNA per unit microbial mass were not consistent during the incubation except during the post-decay phase. Especially within the exponential phase, each showed a 10-fold difference between maximal and minimal values. In this case, the conventional method which converts ATP or DNA concentration into microbial mass using a fixed conversion factor can give inaccurate results. While the constant ratios of 0.74 mg ATP/g VSS and 1.96 mg DNA/g VSS were determined for the post-decay phase, the ATP and DNA concentrations showed strong linear relationships with the microbial mass (r2=0.99) within the ranges of 0.039-1.078 mg ATP/l and 0.075-2.080 mg DNA/l, respectively. The linear regression equations are as follows: (1) microbial mass concentration (mg/l)=478.5xATP concentration (mg/l)+293.5, (2) microbial mass concentration (mg/l)=257.2xDNA concentration (mg/l)+250.4. Therefore, changes in the mass of the acidogenic population should be monitored by the combined use of the regression equations obtained in the exponential phase and the constant ratios determined in the post-decay phase. This procedure should be widely applicable to the acidogenesis of dairy processing wastewaters, especially of a highly suspended organic wastewater such as whey.