Incorporating biodegradation and advanced oxidation processes in the treatment of spent metalworking fluids

Abstract

The treatment of spent metalworking fluids (MWFs) is difficult due to their complex and variable composition. Small businesses often struggle to meet increasingly stringent legislation and rising costs as they need to treat this wastewater on site annually over a short period. Larger businesses that treat their wastewater continuously can benefit from the use of biological processes, although new MWFs designed to resist biological activity represent a challenge. A three-stage treatment is generally applied, with the oil phase being removed first, followed by a reduction in COD loading and then polishing of the effluent's quality in the final stage. The performance of advanced oxidation processes (AOPs), which could be of benefit to both types of businesses was studied. After assessing the biodegradability of spent MFW, different AOPs were used (UV/H2O2, photo-Fenton and UV/TiO2) to establish the treatability of this wastewater by hydroxyl radicals (*OH). The interactions of both the chemical and biological treatments were also investigated. The wastewater was found to be readily biodegradable in the Zahn-Wellens test with 69% COD and 74% DOC removal. The UV/TiO2 reactor was found to be the cheapest option achieving a very good COD removal (82% at 20 min retention time and 10 L min(-1) aeration rate). The photo-Fenton process was found to be efficient in terms of degradation rate, achieving 84% COD removal (1 M Fe2+, 40 M H2O2, 20.7 J cm(-2), pH 3) and also improving the wastewater's biodegradability. The UV/H202 process was the most effective in removing recalcitrant COD in the post-biological treatment stage.

Bioremediation Of A Spent Metalworking Fluid With Auto- And Allochthonous Bacterial Consortia

“…For that reason microbiological remediation has been proposed as an advantageous and high-yield method, which may serve as a cost-competitive, low energy demanding and environment-friendly alternative [10,11,[32][33][34][35][36][37]. The applicability of biological methods is particularly high for the treatment of water-miscible emulsions.…”

“…The annual use of the MWFs exceeds 2 million m 3 worldwide [9,10]; however, the final volume of wastewater discharge may be even 10 times higher since technological processes require MWF dilution. MWFs are usually very chemically complex.…”

“…In addition, water-miscible MWF emulsions can hamper conventional wastewater treatment processes. Therefore the disposal of such waste streams directly to sewage systems is strictly forbidden and manufacturing companies are urged to treat their waste on-site [2,10]. The reuse of spent MWFs is not practically possible due to their chemical ageing and microbiological deterioration [1,4,26].…”

“…The above risks have forced the worldwide environmental authorities to tighten regulations regarding the MWF use, treatment and disposal [9,10,[23][24][25]. In addition, water-miscible MWF emulsions can hamper conventional wastewater treatment processes.…”

“…For the reasons described above there is a strong need to elaborate economically-efficient and technologically reasonable methods to treat the MWFs streams. Most of the efforts taken to date have relied upon physical and chemical treatment or mechanical attempts towards oil phase separation [1,10]. Among the elaborated techniques are: chemical or electrochemical pretreatment (flocculation, coagulation, destabilization, electrochemical splitting), gravity or membrane separation as well as thermal emulsion breaking, vacuum evaporation and finally, incineration [1,2,9,10,[27][28][29][30][31][32].…”