Impact of Hydrogen Peroxide Oxygen Transfer Tests on the Performance of the Biological Nutrient Removal Process

Abstract

Knowledge of in-process oxygen transfer is essential to the optimum design and operation of aeration systems in activated sludge processes. In this study, non-steady state H2O2 oxygen transfer tests were performed in a laboratory scale, University of Cape Town configuration biological nutrient removal process (BNR) to measure the in-process oxygen transfer rates. Given the small quantity (about 1 ml @30% concentration) of H2O2 used in the aerobic reactor with a mixed liquor volume of 161 (total system working volume of 33.65 l), no effect on the process performance itself was expected. However, the process performance data obtained indicated results to the contrary. Use of H2O2 in measuring process oxygen transfer rates may not be suitable for BNR processes, as all the major process performance indicators (carbon, nitrogen and phosphorus removal by the system and carbon uptake and phosphorus release in the anaerobic zone) were negatively affected. Evidence in thiswork leads to the conclusion that external addition of H2O2 leads to excessive production of the hydroxyl radical. Since microorganisms do not have enzyme systems capable of acting upon this additional reactive radical, it resulted in loss of process performance. It is also possible that H2O2 could have upset the normal aerobic respiration process by introducing oxidative stress conditions on the catalase, peroxidase and superoxide dismutase enzymes that deal with other oxygen radicals generated as part of the overall process of reducing oxygen to water. Any test that interferes with the system in which the test is being performed is suspect. Therefore, in light of these results, the H2O2 method to test in-process oxygen transfer should be re-evaluated.

Comparison of Oxygen Transfer Parameters from Four Testing Methods in Three Activated Sludge Processes

“…In addition to the surprisingly high oxygen transfer parameters, the H2O2 addition resulted in rapid increases in ORP and pH and such changes potentially alter the metabolic functioning of microorganisms (Mahendraker et al 2002). This test also led to a loss in process efficiency in terms of COD, ammonia and phosphorus removal by the process (Mahendraker et al 2002, In press).…”

Activated Sludge and Other Aerobic Suspended Culture Processes

“…The impact of hydrogen peroxide on the activated sludge system to measure in process oxygen transfer was studied (Mahendraker et al, 2002). It was found that small amounts of hydrogen peroxide (1 ml at 30% concentration) inhibited carbon, nitrogen, and phosphorus removal in the activated sludge system.…”

Closure

“…After total ammonia oxidation in this reactor, a new ammonia addition re‐established the plateau, with the nitrification process remaining inhibited in reactor 1. The effect of H 2 O 2 addition on process performance observed by Mahendraker et al (2002) may possibly be a result of the duration or mass of the H 2 O 2 addition.…”