Turning treated wastewater into district heating in northwestern China

Before the project, the Chengguan District faced a combination of structural and policy-driven challenges that made conventional solutions increasingly unviable. Lanzhou Thermal Power Group needed to address persistent shortfalls in winter heating coverage while expanding capacity to meet growing demand. At the same time, coal-fired boilers were being phased out, reducing the availability of traditional heat sources and increasing the need for alternatives that could scale. Clean heating had also become a regulatory priority, requiring a solution that could support Lanzhou's decarbonization goals while providing reliable heating.

Adding complexity, the proposed heat source, reclaimed wastewater, presented its own technical hurdles. Following a detailed on-site assessment of the wastewater treatment plant, Johnson Controls identified several operational constraints. Reclaimed water temperatures averaged only around 10°C, limiting heat-exchange efficiency, while the high salinity and corrosive characteristics of treated wastewater placed exceptional demands on long-term equipment durability. Winter startup conditions added another layer of complexity, requiring the system to operate reliably and stably under low-temperature conditions.

In response, Lanzhou Thermal Power Group initiated a phased approach to expand heating capacity without adding carbon-intensive infrastructure. The project was designed in two phases, each planned to serve approximately 1 million square meters, with Phase I centered in Chengguan District to address the most immediate heating needs. Rather than relying on conventional fuels, the Group explored whether treated wastewater could help meet growing heating demand. The city produces approximately 300,000 tonnes of treated wastewater that retains thermal energy from industrial and residential activities.

Working with Johnson Controls, the Group implemented a customized wastewater-source heat pump system centered on five YORK® CYK high-temperature centrifugal heat pump units. The units use ultra-high-pressure-ratio, two-stage compression technology to recover and upgrade low-temperature wastewater heat for use in the district heating network.

To support long-term operation in chloride-rich reclaimed water, evaporator heat-exchange tubes were constructed from corrosion-resistant copper-nickel alloy. The system was designed to address low wastewater temperatures, corrosive water conditions, and the demands of winter operation.

Trial operations began during winter 2024, and Phase I now provides clean and reliable winter heating to approximately 1.5 million m² of residential buildings. By converting previously wasted thermal energy into a productive heating resource, Lanzhou Thermal Power Group expanded heating capacity while advancing Lanzhou's clean-heating and dual-carbon objectives.

Over a single heating season, the system achieved:

• Nearly 273,000 GJ of low-grade heat recovered
• Approximately 37.65 MW of waste heat recovered per hour
• Estimated 9,330 tonnes of standard coal equivalent saved annually
• About 32,000 tonnes of CO₂ emissions avoided each year

The environmental impact is equivalent to planting approximately 1.6 million trees annually. The project also provides residents with a more stable and reliable heating supply while supporting Lanzhou's clean-heating and dual-carbon objectives.

Lanzhou Thermal Power Group provides district heating services in Lanzhou, northwestern China, and is advancing clean-heating and emissions reductions initiatives through circular energy use.