Most of the wastewater from cold rolling in steel mills is discharged intermittently, and the replacement cycle for acid pickling solution, degreasing solution, and emulsion used in rolling mills ranges from two weeks to two months. The flushing water of the rolling mill is generally discharged once a day, and the product cleaning water is also discharged intermittently. The discharged wastewater contains pollutants such as oil, acid, and alkali.

The oily wastewater discharged from the washing of various unit sites, the emulsified and oily wastewater generated from the pit and rolling mill cleaning of the acid pickling rolling mill combined unit, the oily wastewater generated from the cleaning cycle treatment section and pit of the continuous annealing unit, the oily wastewater generated from the degreasing cleaning section and pit of the hot-dip galvanizing unit, the oily wastewater generated from the degreasing cleaning and process section of the color coating unit, the emulsified and oily wastewater generated from the grinding roller room of the machine repair, and the flushing wastewater of the oil depot enter the oily and emulsified wastewater treatment system of the steel rolling mill.

Oil containing and emulsion wastewater enters the wastewater regulation tank, where most of the floating oil is skimmed off. The wastewater is pumped to a paper tape filter for filtration, and then enters the ultrafiltration device. The filtered waste oil is collected for treatment, and the water is sent to the acid-base system for further treatment.

The rinse water and other acid containing wastewater from the pickling unit are discharged into the acid water treatment system. The degreasing wastewater is treated with oil removal and the passivation cleaning water is treated with chromium removal before entering the pickling wastewater treatment system.