Visible light photocatalytic inactivation of Escherichia coli by natural pyrite assisted by oxalate at neutral pH

Abstract

Escherichia coli is the main microbial indicator in water. The enhancement of visible light photocatalytic inactivation of bacteria using oxalate – natural pyrite was evaluated in order to prevent development of disinfection byproducts and cost-effective operation. Influences of operating parameters include light intensity, pyrite dosage, particle size, oxalate concentration; pH, O2, H2O2 and inorganic ions were evaluated in a batch environment. Increase of light intensity, O2 flow, H2O2 concentration, smaller particle size and increased pyrite dosage boosted the inactivation rate of E. coli through more generation of reactive spices (RSs). Oxalate increased inactivation rate of E. coli via increasing release of iron, preventing formation of oxy layer on pyrite surface, high quantum yields of Fe+3 – organic ligand, enhancing permeability of E. coli membrane, increasing pH range close to neutral and visible light region. The scavenging tests confirmed participation of OHb, OHs and ∙O2− as dominant RSs in the system. The influence of inorganic ions on inactivation rate of E. coli was obtained as F−>HCO3−>Ca+2>NO3−>Cl−>SO4−2. The regrowth of E. coli was not observed in the optimum condition. This work suggests that oxalate – natural pyrite complex under light-emitting diode visible light can be a proper alternative for disinfection of natural water.