Fenton Treatment of Cutting Oil Wastewater with Ferric Sludge Reuse for Subsequent COD Removal

Synthetic cutting-oil wastewater was treated by the Fenton process under laboratory conditions at pH 3.00 ± 0.2. Selected Fe2+/H2O2 doses were concentration-specific: 25/125, 75/375, 150/300, and 300/1,500 mg/L for 1.0, 4.0, 9.0, and 22.0 g/L wastewater, respectively. The corresponding COD removals were 88.52%, 87.22%, 90.56%, and 93.24%. An Fe-only control removed 91.41% COD and produced more suspended solids, showing that coagulation/precipitation contributed to the observed COD removal. Ferric-sludge reuse maintained COD removals of 89.35%, 85.12%, and 83.60% during the initial treatment and two subsequent reuse cycles. The treated wastewater remained above the Thai industrial COD limit and remained turbid; therefore, under the conditions studied, Fenton treatment should be considered a pretreatment followed by an appropriate solids-separation and polishing step.