Biosys Journal Biotechnology & Bioengineering
An accurate measurement technique for the biological oxygen uptake rate Date: September 20, 2024
Abstract
Johnny Lee
For any wastewater treatment aeration tank, the paper presents an interesting technique to deal with oxygen uptake rate (OUR) measurements. Aerobic metabolism rates are frequently reflected in oxygen consumption rates, although inorganic carbon remineralization and abiotic reoxidation of reduced species can also contribute to oxygen consumption rates. This paper focuses on the former type of oxygen consumption; hence the technique is primarily related to the biological uptake rate only. It would be fascinating to try the proposed dilution vs. the “shake it up” aeration approach to avoid shearing the floc which may increase the OUR artificially, jeopardizing the true measurement in the aeration tank. In any bioreactor, when the level of dissolved oxygen in the medium falls below a certain point, the specific rate of oxygen uptake is also dependent on the oxygen concentration in the liquid.
Oxygen uptake rate and dissolved oxygen (DO) are inversely proportional to each other. The dissolved oxygen uptake rate (DOUR) test measures the respiration rate of organisms. Since it measures the rate at which oxygen is used (in mg O2/L/hour), it is a useful tool to evaluate process performance, aeration equipment, and biodegradability of the waste. The oxygen uptake rate is one of the fundamental physiological characteristics of culture growth and has been used for optimizing the fermentation process, and so it needs to be measured accurately. Oxygen uptake rate (OUR) is the microorganism oxygen consumption per unit time and is one of the few accessible parameters to quantify the metabolism rate of the activated sludge in a wastewater treatment plant.
The manuscript observes that if a sample of mixed liquor is withdrawn from an aeration tank operating at low DO, the OUR measured in the sample after shaking (or other means of perturbation) will be higher than the true oxygen uptake rate (OUR) which is limited by the aeration supply. Once a high DO is provided, then oxygen is no longer a limiting factor and the OUR will increase. With sufficient DO the OUR will become a function of the substrate concentration and the biomass concentration in the collected sample for measurement. Also, it is possible that the point at which the DO becomes limiting may itself be a function of the OUR. In other words, if a graph of OUR vs DO is made as shown in this document, one may find a different point at which the OUR starts to drop off (as the DO goes from close to saturation to lower levels).
To alleviate the many problems of measurement, the proposed method using dilution with saturated DO may give a more accurate measurement than the current standard method using a sample shaking technique as described in [1]. With a more accurate measurement of the OUR, it may lend credence to justification for the modification of the fundamental equation for oxygen transfer in a respiring system, as applied to an example provided by ASCE/EWRI 18- 18 recently published.