Abstract The river basin that empties into the Atlantic Ocean near the Brazilian city of Aracaju is the most important in the northeast corner of this environmentally sensitive country. The river basin supplies water for Aracaju's 470,000 inhabitants, as well as for many sugar cane plantations and cattle ranches in the region. Protecting that water supply was a major concern for Schlumberger operations based in Aracaju. The city's water is collected and treated from the Poxim River that flows close to the base. To ensure no contaminated water reaches the river, Schlumberger recently built an organically based wastewater treatment plant that has eliminated all sewage emissions. As a result of the new wastewater treatment plant, the Schlumberger base in Aracaju achieved the following results: Contributed to protection of local water supply Achieved significant reductions in harmful discharges Completely eliminated sewage emission into the Poxim River Received recognition from state environmental agency Eliminated odors and enhanced local vegetation In 2003, Schlumberger built a wetland tank to collect and treat effluent water from the base, which houses up to 120 employees. The new sanitation installation was built as a requirement to comply with local regulations, established in 2002, in order to renew the state environmental license for the base. The wetland tank replaced septic tanks that used to discharge used water into the Poxim River. The Aracaju Water Treatment Station collects its water from the river. Now, instead of being released into the river, effluent water is stored and re-oxygenated in a 37-cubic-meter cement treatment tank filled with coarse gravel in which Tabua plants live. The water treatment plant uses no mechanical devices. Rather aerobic and anaerobic chambers are used to degrade organic material. The final effluent water is evaporated in a wetland and any excess is used to irrigate grass and trees of the base. With this system, the treatment plant has achieved significant reductions in chemical oxygen demand, oxygen consumption and fecal coliforms. The discharge rates for these are significantly lower than those allowed by the new local environmental regulations. In addition the base has completely eliminated sewage emission into the Poxim River. The Schlumberger base was recognized by the state environmental agency that inspected the new plant in July/2004 to issue the environmental license. The agency took photographs and requested that plant be copied at other industrial installations at Sergipe State as part of environmental licenses locations. Also, the base's neighbor, a state finance agency, congratulated the base on the elimination of foul odors. Visually, the grass at the base entrance now is continuously green.