Distribution and transfer of organics in the coagulation–anaerobic hydrolysis–aerobic treatment process of cutting fluid wastewaters

Two kinds of real cutting fluid wastewater samples (i.e., sample A and sample B) and two kinds of coagulants (i.e., polymerized aluminum chloride (PAC) and polymeric iron sulfate (PFS)) were studied during coagulation experiment, and the coagulation effluent of sample B with PAC was utilized for subsequent anaerobic hydrolysis–aerobic treatment, and the molecular weight (MW) distribution and ultraviolet (UV) absorption spectroscopy were used to explore the distribution and transfer of organics of each treatment unit. The results showed that sample A and sample B both mainly contained macromolecular organics with MW > 100 kDa and small molecule organics with MW < 3 kDa, and PAC had significant coagulation performance for organics with MW > 100 kDa in both samples, while neither PAC nor PFS achieved good coagulation performance for the small molecule organics with MW < 3 kDa in both samples. It could be inferred by UV spectra that the coagulation effluent of sample A and B might both contain organics with conjugated double bonds, monocyclic aromatic hydrocarbons, and the coagulation effluent of sample B might also contain polycyclic aromatic hydrocarbons and heterocyclic compounds with low MW. MW distribution analysis and the UV spectra results showed that biological treatment could further remove organics with conjugated double bonds and aromatic compounds with MW < 3 kDa. HIGHLIGHTS Two kinds of real cutting fluid wastewater mainly contained organics with MW > 100 kDa and with MW < 3 kDa.; PAC had a significant coagulation performance for organics with MW > 100 kDa in both samples.; Neither PAC nor PFS achieved good coagulation performance for organics with MW < 3 kDa in both samples.; Biological treatment could further remove organics with conjugated double bonds and aromatic compounds with MW < 3 kDa.;