Potential effects of rainwater-borne hydrogen peroxide on pollutants in stagnant water environments

- Stagnant water environments are subject to chemical and microbial contamination.
- Microcosm experiments using canal and urban lake water as example stagnant water.
- Synthetic rainwater-borne H2O2 reacted with water-borne Fe2+ to trigger Fenton reaction.
- Coliforms, ammonia-oxidizing microbes and organic pollutant-degraders were inactivated.
- Nitrite and PAHs can be chemically decomposed by OH generated from the reaction system.

Microcosm experiments were conducted to examine the effects of rainwater-borne H2O2 on inactivation of water-borne coliforms, oxidation of ammonia and nitrite, and degradation of organic pollutants in canal and urban lake water. The results show that the soluble iron in the investigated water samples was sufficiently effective for reaction with H2O2 in the simulated rainwater-affected stagnant water to produce OH (Fenton reaction), which inactivated coliform bacteria even at a H2O2 dose as low as 5 μM within just 1 min of contact time. Coliform inhibition could last for at least 1 h and repeated input of H2O2 at a 30 min interval allowed maintenance of microbial inhibition for at least 3 h. Nitrification was also impeded by the Fenton process. The resulting inhibition of ammonia-oxidizing microbes reduced the removal rate of NH4+ and the emission of gaseous N species. In the presence of H2O2 at a dose of 20 μM, Fenton-driven chemical oxidation appeared to outplay the impediment of biodegradation caused by inhibited microbial activities in terms of removing total polycyclic aromatic hydrocarbons from the water column. The findings point to a potential research direction that may help to explain the dynamics of water-borne pollutants in ambient water environments.