The effect of hydrogen peroxide on the biochemical oxygen demand (BOD) values measured during ionizing radiation treatment of wastewater

Abstract

As biochemical oxygen demand (BOD) properly illustrates transformation of toxic organic compounds to harmless and biodegradable substances, it is often used to demonstrate the efficiency of wastewater treatment technologies. Nevertheless, H2O2 can form when solutions are subjected to advanced oxidation processes (AOP). H2O2 production is typical in high energy irradiation treatments. Toxic effect of H2O2 on microbes is a well known fact in the field of biology, however, the impact of H2O2 is usually not taken into account when evaluating effectiveness of AOP. To quantify the impact of the forming H2O2 on the outcome of BOD tests, the BOD of glucose-glutamic acid reference solution was determined in the presence of hydrogen peroxide in the 0.1 and 75 mg dm−3 concentration range. Results showed that H2O2 distorts the BOD measurement in two ways. Prolonged lag period takes place that ensures adaptation of microbes to toxic environment and promotes production of catalase enzyme that decomposes hydrogen peroxide. On the other hand, appearance of catalase producing bacterial groups leads to reduced BOD values because the oxygen released from the H2O2 results in a negative error as it acts against oxygen depletion. The correlation between H2O2 concentration and the shift in lag period was described, as well as the relationship between the initial H2O2 concentration and the final BOD results. To validate the effects studied, BOD was measured in 0.1 mmol dm−3 oxacillin solutions irradiated with gamma rays. It was confirmed that the presence of H2O2 may lead to underestimation of the actual BOD as increase in BOD was observed when hydrogen peroxide was eliminated from the solution before starting the measurement.