Increasingly stringent discharge regulations have impacted manufacturing operations globally, making the proper disposal of spent metalworking fluids (MWFs) imperative. The requirements vary among regions, countries, states, and provinces, but generally include both conventional and nonconventional pollutants. The US Environmental Protection Agency (EPA) has passed numerous laws to protect the nation's waterways. MWF wastewater is comprised of many sources, not just coolants and washing soaps. The influent characteristics and the volume of wastewater to be treated dictate the most effective wastewater treatment plant (WWTP) design. Metalworking operations typically generate two types of wastewater: dilute oily wastewater and concentrated spent MWFs. Chemical emulsion breaking requires intimate mixing of the wastewater with the emulsion-breaking chemicals, followed by flocculation and flotation. Biological systems have become an increasingly popular method of treatment of MWF wastewaters. Biological digestion is an appropriate treatment for biodegradable organic compounds.