Abstract
Recently, the disposal of waste oil-in-water cutting emulsion has become an urgent issue because of its extremely high chemical oxygen demand (COD). The present work focuses on treating the waste cutting emulsion generated from the Samsung Thai-Nguyen factory in Vietnam. This work used multistage methods to treat the waste cutting emulsion to meet the wastewater disposal requirement and characterize the oil recovered. The multistage methods consist of the flocculation method (stage 1) and Fenton oxidation (stage 2). The wastewater after stage 1 treatment has a COD reduction efficiency of 98.24% at the condition of pH 5, Al2(SO4)3 2 g/L, C-PAM 12 mg/L, stirring speed 50 rpm, and stirring time 15 minutes. At that condition, the COD value decreased from 147200 mg/L to 2484 mg/L. After stage 2, the COD value further decreased from 2484 mg/L to 85.4 mg/L with total COD removal efficiency increasing to 99.9% at the optimum conditions of pH 3, H2O2 : FeSO4 concentration ratio of 10 : 1, and FeSO4 concentration of 14.04 g/L. After the stage 2 treatment, the wastewater with the COD value of 85.4 mg/L and BOD5 value of 30 mg/L satisfied the Vietnam standard grade B and grade A, respectively, for industrial wastewater. The oil recovered from the treatment has a heating value of 38095 ± 8 kJ/kg, and thus, it could be reusable as fuel gas.
Highlights
Metal cutting emulsions or cutting fluids play an important role in the machining process. ey are frequently used in metalworking industries for several reasons, such as lubricating and cooling the machine
cationic polyacrylamide (C-PAM) is a positively charged organic polymer used as a water treatment flocculant aid [23]. e Fenton oxidation was selected as stage 2 for the treatment. e hydroxyl radical produced from advanced oxidation can decompose the residual oil and other contaminants into harmless substances such as CO2 and water [24]
Results from Stage 1: Flocculation Treatment. e flocculation treatment of the oil cutting emulsion was carried out using Al2(SO4)3 and cationic polyacrylamide (C-PAM) as the flocculant and flocculant aid, respectively
Summary
Metal cutting emulsions or cutting fluids play an important role in the machining process. ey are frequently used in metalworking industries for several reasons, such as lubricating and cooling the machine. Ese emulsions are formed by blending oil and water for about 3–15% oil concentration and the emulsifiers for more stable emulsion [5] Despite their huge advantages, cutting emulsions is becoming the main source of oil-contaminated wastewater in metal industries. It is estimated that more than 1000 million gallons of the cutting emulsions are disposed of each year in the USA, and the amount of wastewater may increase a lot after using [7, 8]. It brings about more challenges for the treatment to meet the requirement of the standard for discharging fluids. C-PAM is a positively charged organic polymer used as a water treatment flocculant aid [23]. e Fenton oxidation was selected as stage 2 for the treatment. e hydroxyl radical produced from advanced oxidation can decompose the residual oil and other contaminants into harmless substances such as CO2 and water [24]
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