New High

Lhasa Najin WTP setting global standards

China houses the world’s largest municipal wastewater infrastructure asset. The cou­ntry’s wastewater treatment plant (WWTP) is focused on employing low-carbon concepts and adopting global advanced technologies that are engineered in line with its sustainable development strategy. It aims to become a global standard for municipal WWTPs. The Chi­na National Development and Reform Commis­sion has also recently issued guidelines for promoting the use of wastewater as a resource, whi­ch will aid in the development of WWTPs.

The Lhasa Najin water treatment plant (WTP) was established in 2017 at a cost of approximately $213 million and is designed to treat a flow of 480,000 m3 per day. This plant, which is located on the Tibetan plateau in China’s Tibet Auto­nomous Region, is the world’s largest WTP for surface water in the area, as well as the world’s highest ultraviolet (UV) disinfection WTP at 3,658 metres.

Salient features

The plant has the capacity to supply the daily water needs of 1 million people in the plateau’s central region, near the Himalayas. Many districts in Lhasa, including Chengguan District, Liuwu New District, and the Lhasa Economic and Tech­nological Development Zone, receive water from the plant. The Najin WTP has addressed many of the issues faced in the original WTP due to limited water supply and use of conventional water treatment procedures. The up­graded plant uses a combination UV-ch­lorine disinfection technique, which swiftly and efficiently inactivates disease-causing mi­cro­orga­nisms while also lowering the amount of various disinfection by-products in the water, as­suring clean and safe drinking water for Lhasa’s residents.

Throughout the plant, an in-pipe medium pressure UV system (Onyx-WH-12) with an input power of 72 kW and an output power of 10.8 kW is used. To achieve a 4-log microbial inactivation rate, the system has a photoelectric conversion efficiency of 15 per cent and an effective dose of more than 40 millijoules per cm2. In addition, the UV system’s medium pressure UV lamp has a service life of more than 9,000 hours, and its daily operation and maintenance costs are less than CNY 0.02 per tonne of water, making this approach exceptionally efficient and cost-effective.

Technology showcase

Tsinghua University and the Beijing Onyx Envi­ronmental and Research Institute for Envi­ron­mental Innova­tion (Suzhou) have collaborated on UV disinfection research and development for nearly 20 years. Some of the technologies that have been developed are third-generation reactor with co­mputational fluid dynamics simulation technology for quick, efficient and thorough system sterilisation; an online automatic cleaning system with a spiral cleaning structure that fully guarantees cleaning and maintains the casing transmission rate above 90 per cent for a long period of time, resulting in a stable UV dose output; a ballast with double cooling mode that can be intelligently controlled based on water quality and quantity to ensure long-term stable operation of systems; a level-2 equipment protection system prevents the surface temperature from rising too high during the operation of medium voltage equipment and internet of things cloud control technology that allows the central control room and mobile phone apps to monitor the treatment processes off-site in real time.

The Lhasa Najin WTP’s UV disinfection process is an excellent example of academia and industry working together to do independent and innovative research and development to improve ac­c­e­ss to clean and safe water. The project receiv­ed an honourable certificate from the E20 Envi­ron­mental Platform for “Outstanding Solu­tions in Water Supply Industry – Quality Water Supply Providers” for 2019-20.

During the Thirteenth Five-Year Plan period, Tibet concentrated on making up for municipal infrastructure deficiencies, and completed the construction of nine water supply plants, including the Najin water plant in Lhasa. The urban public water supply penetration rate in the entire district reached 94.75 per cent at the end of 2019, an increase of 9.75 percentage points from the end of the Twelfth Five-Year Plan period.

In sum

Sewage treatment plays a key role in enhancing the environmental quality, pollution prevention and ecological protection, and ensuring sustainable economic and social development. The Lhasa Najin WTP has set an example for technology use in efficient water treatment. The plant is aims to achieve sustainable water quality, re­sour­ce recovery, energy neutrality and environmental friendliness. It is deploying the latest me­thods to conduct revolutionary research to improve access to clean and safe water.