COST-EFFECTIVE WASTEWATER REUSE AT AN AUTOMOTIVE ASSEMBLY PLANT

An extended drought and extensive population growth has created a severe water shortage in the Sonoran Desert where the Ford Hermosillo Stamping & Assembly Plant (HSAP) is located. Residential users have been forced into a serious curtailment program while the city pursues conservation, rate increases, and curtailment for industrial users. HSAP, being one of the larger water users, is under extreme pressure to reduce water consumption and has reduced water usage by ∼65% over the past 8 years.However, a new program destined for the HSAP that will increase production by 60% would increase water consumption from 127 to 178 million gallons per year (MGY) if no actions were taken. Therefore, a facility upgrade was approved to ensure that no additional consumption occurs as production is increased (that is, “water neutrality”). Twenty-three options to reduce city water usage were identified and the water savings, capital cost, and operation and maintenance costs for each alternative were quantified.The chosen technology was combined treatment of sanitary and pre-treated process water by membrane biological reactor (MBR) followed by reverse osmosis (RO). To maintain water use neutrality, 51 MGY had to be reused, of which 15 MGY could be reused by the site's irrigation system, and 36 MGY reused in cooling towers and the paint shop phosphate and E-coat operations.Treatment plant improvements were designed and constructed to maximize water reuse at the lowest life-cycle cost. Maximum reuse of existing infrastructure provided the smallest footprint and minimal interconnections. Total installed facilities provided MBR treatment of 350,000 gallons per day (GPD) for 1,672,000 (4.18 per installed GPD) and RO treatment of 225,000 GPD for 170,000 (0.75 per installed GPD).