General Motors Cactus Plant | Water Reuse ZLD System

The Client's Needs

The General Motors Cactus Plant in San Luis Potosi, Mexico, is an automobile assembly plant situated in an area with limited-capacity deep wells that supply the production facility with process water. Due to the arid, remote location, no receiving stream or municipal sewer is available to receive wastewater generated by the plant. For these reasons, the plant needed a zero liquid discharge solution designed to maximize water reuse. The facility generates process water from various automotive manufacturing operations, as well as sanitary wastewater. The process wastewater contains high concentrations of dissolved metals, phosphates, free and emulsified oils, dissolved organics, and silica. Typically, automotive wastewater is pretreated and discharged to a municipal wastewater treatment plant. With no municipal facilities in the area, an innovative option had to be developed.

Our Solution

The process wastewater from this assembly plant is pretreated for oil and grease and metals removal. It is then combined with the sanitary waste and treated by a conventional activated sludge process for organics removal. Following this treatment, the wastewater contains 1,000 to 1,500 mg/l total dissolved solids (TDS), 25 to 35 mg/l silica, and 18 to 35 mg/l of dissolved refractory organics. The water is then processed by Veolia Water Solutions & Technologies' proprietary OPUS® technology, where the TDS and dissolved organics are removed so that the water can be recycled for reuse.

The goal of the OPUS® technology is to convert 90% of the tertiary wastewater into reusable water. This technology consists of multiple treatment processes including degasification, chemical softening, media filtration, ion exchange softening, and reverse osmosis technologies. The pretreatment processes ahead of the RO are designed to reduce the hardness, metals and suspended solids in the feed water. The RO process operates at an elevated pH, which effectively controls biological, organic and particulate fouling, eliminates scaling due to silica, and increases the rejection of organics. The reject water is sent to solar ponds at the site for evaporation.

Scope of Work and Technologies

The GM Cactus Plant project involved process design, basic engineering and equipment supply. The advanced water treatment system includes the equipment shown in the process diagram below.



Constituent Wastewater Quality Achieved

TDS, mg/l



SILICA, mg/l



TOC, mg/l



COD, mg/l



BOD, mg/l









RO CIP Requirements: once in 4 to 6 months