PretreatmentThe refinery wastewater was pretreated in two steps. Thesuspended solids, immiscible liquids, solid particles, andsuspended substances were reduced significantly by grav-ity in separation tanks at National Refinery Limited (NRL)site, Karachi, Pakistan. Then concentration of heavy metaland small sized suspended solids were reduced in secondstep in Chemical Engineering Labs at Karachi University(KU), Karachi, Pakistan. The pretreated refinery wastewatersamples were tested for measurement of parameters. Afterupgrading and expansion completed recently, the NRL isdesigned to process 53,000 bpsd crude oil of local and ArabianGulf origin; 6600 bpsd of lube fraction; and producing premiumproducts by deeper conversion of the low value high sulfurfuel oil and asphalt. Table 1 shows the characteristics of the