Treatment and biodegradability enhancement of metalworking fluids by the Fenton and Fenton-like processes: Effect of some variables

The Metalworking or cutting fluids (MWCFs) used as a coolant and lubrication in by different metal working operations and machinery processes. Treatment of this kind of wastewater imposes an excessive cost on metalworking industries. The worldwide usage is estimated about 3.8–7.6 million m3 of oily wastewater results annually from the use of MWCFs. Fenton and Fenton-like processes is applied for the treatment of MWCFs characterized by high COD concentration and non-biodegradability. Affecting the processes, such as pH, dosages of Fe2+ (and Fe3+) and H2O2, the contact time, mixing speed were determined by Jar-test experiment, also according to dual functions of oxidation and coagulation in Fenton process, the sludge production rate and sludge settling velocity were determined in a graduated cylinder.The results of study showed the optimum conditions, the amount of COD removal was 88.31% in Fenton Process under pH 3, 50 g/l H2O2, 10 g/l Fe2+ and 60 min settling time, and 73.97% in Fenton-like Process under pH 5, 100 g/l H2O2, 10 g/l Fecl3 and 30 min settling time. Also, during the first 15 min of the Fenton’s reaction, more than 92% of COD removal could be achieved. The efficiency of the Fenton-like process was less than Fenton processes. The Fenton process, when increasing the dosages of Fe2+ from 5 to 40 g/l, the sludge production rate increasing from 55 to 580 ml/l but also increasing sludge settling velocity.After all processes, the biodegradability (BOD5/COD ratio) of the treated MWCFs was increased compared to that of the raw MWCFs and the highest increase in BOD5/COD ratio was observed in the Fenton process.

Keywords:

metal cutting fluids , wastewater treatment , Fenton’s reagent , Oxidation , Hydroxyl radical