Dose-dependent decomposition rate constants of hydrogen peroxide in small-scale biofilters

This study investigated rates of hydrogen peroxide (H2O2) degradation in biofilters, to provide information for more accurate treatment regimes in recirculation systems and more accurate prediction of effluent H2O2 concentrations. Sodium percarbonate (2Na2CO3·3H2O2) was applied to small-scale recirculation systems with active bio filters.

Three different treatment dosages corresponding to an initial hydrogen peroxide (H2O2) concentration (C0) of 13.0, 26.0 or 39.0ppm were used (N=18). Decomposition rate constants (ke) of H2O2 were identified by exponential regression analysis of recurrent water samples from treatment start to complete decomposition.

The chemical fate of H2O2 obeyed first order kinetics with half-lives inversely correlated with C0. Decomposition rate constants were significantly related to the amount of organic matter (BOD5) and initial dosage of H2O2, and ranged from ke=0.451 (C0=26ppm; BOD5=2.0mgO2/l) to ke=3.686h−1(C0=13ppm; BOD5=16.1mgO2/l).Surface specific reduction (SSR) of H2O2 in biofilters was positively related to dosage concentration for both levels of BOD5, where SSR from 55 to 220mgH2O2m−2t−1 were found.Oxygen liberation was positive correlated to C0 and BOD5, indicating that hyperoxic conditions can arise if large amounts of sodium percarbonate are added to water with high organic matter content.This study assesses the environmental fate of H2O2 in a closed recirculation system with biofilters, simulating recirculation aquaculture systems.

The information can be applied to hydraulic model to predict actual treatment concentrations in aquaculture facilities and to assess effluent pulse from simulated treatment regimes.