The deep treatment adopts "ultrafiltration + DKRO + RO" and "ultrafiltration + DKRO + DWRO + RO", in which the concentrated liquid of DKRO in the second process enters the SWRO system to improve the water recovery rate and reduce the evaporation of wastewater, and the concentration produced by DWRO enters the evaporation system to realize the recovery of crystalline salt of sodium sulfate and sodium nitrate.