Biodegradation of octylphenol polyethoxylates by denitrification

The biodegradation route of the octylphenol ethoxylates (OPEOs) by denitrification in an upflow anoxic sludge blanket (UASB) reactor was studied. An anaerobic sludge adapted to denitrifying conditions with acetate was adapted with increasing amounts of OPEOs and diminishing amounts of acetate until only 300 mg.L^-1 of OPEOs were fed. Only 70% of stoichiometric NO₃^- was fed so partial removal was expected. The total OPEOs fed was transformed with 70% COD removal. HPLC and GC-MS analyses showed that octylphenol (OP) was immediately formed but disappeared while other intermediates, the ethoxylated moieties; mono and diethoxylate (OPEO₁ and OPEO₂ respectively) led to the cleavage of the alkyl chain to form propylphenol triethoxylate (PPEO₃) and heptylphenol diethoxylated (HPEO₂). These last two compounds are produced due to an attack to both sides of the molecule; the hydrophilic and the hydrophobic. These findings suggest three simultaneous routes of OPEO degradation.