In June of this year, the largest and most advanced wastewater treatment facility in Mongolia—the Ulaanbaatar Central Wastewater Treatment Plant—officially commenced operations. Serving as the project's lead interpreter, Mongolian employee Urna has been diligently moving between various workshops across the facility in recent months, providing interpretation for Mongolian technical staff while systematically organizing the complete operations and maintenance documentation, all in preparation for the plant's handover.

Constructed by China Railway No.4 Engineering Group Co., Ltd. (CTCE Group) using Chinese standards and technology, this treatment plant represents a key ecological cooperation project between China and Mongolia. Covering approximately 178,000 square meters with 55 individual buildings, the facility boasts a daily treatment capacity of 250,000 cubic meters, capable of processing the vast majority of Ulaanbaatar's domestic and industrial wastewater while serving nearly half of Mongolia's population.

Standing on the fourth-floor rooftop of the administration building, eight massive secondary clarifiers spread out like mirrors, their crystal-clear water reflecting the blue sky and white clouds. Inside the main lobby, two display boards create a striking contrast—one showcasing the new energy-efficient, intelligent, and resource-recycling water plant, the other depicting the old facility with its insufficient capacity and outdated equipment.

Lu Haiyun, the project manager for CTCE Group, highlighted the pollution treatment challenges the city once faced: the original plant was built in the 1960s and underwent three expansions, yet its maximum daily treatment capacity remained only 160,000 to 170,000 cubic meters. As the city's population surged, wastewater discharge increased, aging equipment frequently malfunctioned, and the facility could no longer keep pace with urban development. For years, large volumes of inadequately treated sewage flowed directly into the Tuul River, Ulaanbaatar's mother river, leaving the water perpetually emitting a pungent odor—a reality Urna knows all too well. When she first joined CTCE Group a decade ago, she worked on the company's disability rehabilitation center project for children in Mongolia, and she recalls, "We could always smell the foul stench from the river near our accommodation."

Now, with the new plant operating steadily, both the surrounding air quality and river water conditions have improved significantly. Lu Haiyun noted that this facility aims to deliver more than just clean water—it aspires to export a low-carbon, circular economy philosophy. From the design stage, the project incorporated an integrated system combining wastewater treatment, clean energy generation, and resource recovery. According to Lu, the design team capitalized on the high organic content of Mongolian sludge by installing four large-scale mesophilic anaerobic digesters. These digesters ferment sludge to produce biogas for power generation, enabling the plant to achieve approximately 25% to 30% self-sufficiency in electricity and sludge heating needs once fully operational, dramatically reducing long-term operational costs.

From polluted runoff to clean water flowing into the river, this project not only fills a technological gap but also places significant emphasis on cultivating local talent and ensuring independent operations and maintenance. Since 2023, approximately 70 Mongolian operations and maintenance personnel have traveled to China for professional training. Just recently, Urna accompanied local government officials to Beijing for specialized biogas power generation training. "Many Mongolian engineers feel they have gained tremendous knowledge and made great progress through this experience. For me personally, through the learning and growth this project has provided, I am confident I can take on other similar projects in the future," Urna said.