Treatment of triethyl phosphate wastewater by Fenton oxidation and aerobic biodegradation

The conventional (i.e., aerobic biodegradation) and advanced (i.e., Fenton oxidation) treatment methods with implementation potentials were in parallel investigated for the treatment of industrial wastewater rich in organic phosphorus (Org.-P, dominated by triethyl phosphate (TEP)). Fenton effectively reduced Org.-P from 58 to 5 mg/L under the optimal reaction conditions of 20 mM H₂O₂, 14 mM Fe²⁺, pH 3.0, 120 mins' reaction time and the continuous dosing method (N = 4), following the first order kinetic model with a reaction rate constant of 0.07 min^-1. Nevertheless, the pretreatment prior to Fenton reaction (e.g., desalination) is recommended since high salinity significantly hindered TEP degradation, possibly due to the formation of Fe-Cl complexation and its scavenging effect to ∙OH. The Org.-P mineralization rate of ~98% was achieved by aerobic biodegradation. The excellent performance was maintained up to a salinity of 4.6% (w/w), higher than which the mineralization was seriously deteriorated. The high salinity could inhibit the microbial growth. This property might be responsible for the insufficient Org.-P removal during the on-site wastewater biological treatment. The Org.-P and COD concentrations were 6 and 405 mg/L respectively after the realistic wastewater treatment by biodegradation and coagulation, which meets with the municipal sewer discharge standard (GB/T 31962-2015).