Challenge

DaimlerChrysler built an assembly plant for Dodge Ram pick-up trucks in northern Mexico in 1994.  The production lines operate at a rate of 30 vehicles per hour requiring thousands of gallons of fresh water for both industrial and potable water usage.  All wastewater generated from the facility would have to be treated to stringent effluent limits prior to discharge to a small river.  This river runs dry at times and the plant discharge would make up its entire flow.

In the middle of the northern Mexico desert, water is limited and expensive.  Although there are wells located on company property, DaimlerChrysler is still required to pay 6 peso per cubic meter for the water (in 1994, the water costs equated to $7.57 per 1,000 gallons).  An additional cost was incurred in order to pretreat the water prior to use in the facility.

Solution

The final treatment process design includes five key components:

- Potable water treatment to supply drinking water and non-critical industrial applications – aeration to remove hydrogen sulfide followed by chlorination

- Industrial water treatment system to upgrade the well water quality to the levels required for plant industrial processes – reverse osmosis to remove TDS, chlorides and silica

- Sanitary wastewater system for all domestic wastes – system designed to reduce BOD from 300 mg/L to less than 30 mg/L, includes equalization and aeration, clarification, extended aeration and chlorination for final disinfection

- Industrial wastewater system to pretreat and recover all industrial wastewaters - system designed for maximum recovery and reuse and includes batch treatment for metals removal, RBCs for BOD/COD removal, multimedia filters, and reverse osmosis

- Evaporation ponds to dewater produced salt brines

Results

- DaimlerChrysler recovers more than 100,000 gallons per day.
- The cost of reclaiming the water (including chemicals, electricity, etc.) is approximately $8.36 per 1,000 gallons which is currently more economical than purchasing and pre-treating well water.