[Chinese Mainland] Making the Most of Sludge: Yantai Establishes a Full Chain of Biogas Power Generation–Collaborative Incineration–Slag Brickmaking, Cutting Over 3,000 Tons of Carbon Annually

Key Highlights: After completing the renovation of its sludge digestion system, the Yantai Taozhiwan Wastewater Treatment Plant has increased annual biogas production by 210万 cubic meters, bringing total output to 390万 cubic meters; the supporting biogas power generation system achieves combined heat and power (CHP), saving 300万 kWh of electricity annually. Meanwhile, all sludge from the three wastewater treatment plants in the urban area enters the "sludge—incineration—power generation—brick making" collaborative disposal chain, with all furnace slag fully utilized as resources, achieving full coverage of harmless treatment of urban sludge, and reducing carbon dioxide emissions by more than 3000 tons annually.

I. Renovation of the Old Digestion System Boosts Biogas Production

The sludge digestion system at the Taozhiwan Wastewater Treatment Plant has been in service for more than 20 years, and after long-term operation, its equipment has aged and its efficiency has declined. This round of renovation focuses on two areas: renovation of the biogas mixing system and replacement of major equipment.

The renovation effect is directly reflected in gas production: annual biogas production increased by 210万 cubic meters, bringing total system output to 390万 cubic meters.

After commissioning, the supporting biogas power generation system achieves combined heat and power (CHP), saving 300万 kWh of electricity annually. Under the design of cascaded energy utilization, the electricity generated by biogas power generation is directly used for plant equipment operation, while the waste heat generated during power generation is reused to heat the digestion tanks—sludge anaerobic digestion itself requires maintaining mesophilic or thermophilic conditions, and waste heat reuse precisely fills this energy consumption gap, forming an internal energy loop of "gas production—power generation—waste heat—gas production."

On the large screen in the central control room, the operating data of the biogas generator units and the daily power generation are continuously updated and accumulated. For a wastewater treatment plant, this means a reversal of its energy role: from a pure major electricity consumer to a partially self-supplying energy-producing unit.

II. Collaborative Incineration: Sludge Co-fired with Waste and Coal

Biogas power generation only consumes the organic components in sludge; how to dispose of the remaining residual sludge is another question.

At the Yantai Runda Waste Treatment Project site, sludge from wastewater treatment plants is mixed with domestic waste and a small amount of coal in a certain proportion before being fed into the incinerator. The heat energy generated by high-temperature incineration is used for clean power generation, the tail gas is purified and discharged up to standard, and the furnace slag after incineration is collectively transferred to building materials enterprises.

In the building materials production workshop, the furnace slag undergoes crushing, screening, molding, and other processes, ultimately becoming construction bricks. Thus, the sludge disposal pathway is fully closed:

Sludge → Collaborative Incineration → Clean Power Generation → Slag Brick Making

The value of this chain lies in "neither end going to landfill": organic components are converted into biogas energy through anaerobic digestion, inorganic components are converted into building material raw materials after incineration, and all furnace slag is utilized as resources and no longer enters landfills, effectively reducing the risk of secondary pollution.

In fact, Yantai started early on this path. As early as 2010年, the Xin'an River Wastewater Treatment Plant used a German-Chinese financial cooperation loan to build Shandong Province's first sludge co-incineration demonstration project, with a treatment capacity of 50 tons/day, pioneering the co-firing of sludge and coal for power generation. Today, all sludge generated by the three wastewater treatment plants in the urban area enters the collaborative incineration disposal process.

III. Pollution Reduction and Carbon Reduction Account: Annual Carbon Dioxide Emissions Reduced by More Than 3000 Tons

The "ecological account" provided by the Yantai Urban Management Bureau includes three levels.

The first level is harmlessness. The incineration process can effectively remove toxic and harmful substances and pathogens in sludge, pollutant emissions are strictly controlled, and the potential risks of soil and groundwater pollution that may be caused by landfill are fundamentally eliminated. All sludge in the urban area achieves full coverage of harmless treatment.

The second level is carbon emission reduction. After the Taozhiwan sludge digestion renovation, biogas power generation saves 300万 kWh of electricity annually, equivalent to saving a large amount of fossil energy consumption; annual carbon dioxide emissions are reduced by more than 3000 tons.

The third level is avoiding fugitive emissions. Sludge disposal achieves fully enclosed operation throughout the chain, avoiding the uncontrolled fugitive release of greenhouse gases such as methane. The 100-year global warming potential of methane is far higher than that of carbon dioxide. If the sludge anaerobic digestion process is poorly managed, fugitive methane will directly offset the carbon reduction benefits of energy recovery—therefore, "enclosure" itself is a carbon reduction measure, not merely an environmental management requirement.

With three layers stacked, the synergistic effect of pollution reduction and carbon reduction is significant. This "treating waste with waste and turning waste into treasure" model transforms sludge from an environmental burden into energy and building material resources, achieving a closed-loop flow of "resources—products—renewable resources."

IV. Where Is the Replicability

The reference value of the Yantai model lies not in how novel the technologies are—anaerobic digestion, synergistic incineration, and slag brickmaking are all mature processes—but in the combination approach and operational management.

• Prioritizing retrofitting of existing assets—The Taoziwan system is an old facility that has been in operation for over 20 years. Through stirring system retrofitting and equipment renewal, it achieved a substantial increase in gas production, demonstrating that many existing digestion systems have underestimated potential for tapping.
• Cascading energy utilization—Power generation for self-use + waste heat returned to the digestion tanks uses every unit of energy twice, which is the key to improving project economics.
• Cross-industry synergy—Sludge, domestic waste, and coal are co-processed in the same furnace, leveraging the treatment capacity and tail gas purification systems of existing waste incineration facilities, avoiding the high investment of building dedicated facilities for sludge alone.
• Full-chain ledger—Every ton of sludge is traceable and accountable. This is not only an environmental management requirement but also a prerequisite for carbon emission reductions to be calculable and tradable.

For many small and medium-sized cities facing "difficult sludge disposal outlets," these four points offer more reference value than specific process parameters: first revitalize existing assets, then open up cross-industry synergy, and finally use ledgers to turn environmental benefits into measurable assets.

V. Industry Background: Sludge Disposal Remains a Weak Link in Water Treatment

Compared with the rapid upgrading of standards in the wastewater treatment stage, sludge disposal has long been a weak link in the industry. With the 2026年8月15日 of the Ecological Environment Code of the People's Republic of China coming into effect, full life-cycle closed-loop control of pollutants has been written into the codified framework, and as the end product of the wastewater treatment chain, sludge is subject to increasingly stringent harmless disposal and resource utilization requirements.

At the same time, among the two ecological environment labeling standards reviewed and approved at the 2026年9月23日 Executive Meeting of the Ministry of Ecology and Environment, there is "Ecological Environment Labeling - Solid Waste Storage (Disposal) Facilities", which brings solid waste storage and disposal facilities under unified labeling management. For the sludge disposal stage, this means that standardization requirements for storage, transfer, and disposal facilities will be further raised.

Against this background, the combined pathway of "energy recovery + building material utilization + full-process ledger" represented by Yantai has strong demonstration value: it responds to the rigid requirements of harmless disposal while transforming a disposal cost center into a stage with energy and material returns.

Sludge is never "waste that has been treated," but rather "a resource in the wrong place." Yantai's practice provides a quantifiable answer: the sludge from every wastewater treatment plant could be the starting point for the plant's electricity meter to run backward.

About TIANYI TECH

Hong Kong TIANYI Technology Limited (TIANYI LIMITED) focuses on industrial water treatment and water resource reuse. Centered on three core products—Industrial Wastewater Treatment AI Agent, Industrial Water Reuse Optimization System, and Industrial Water System Digital Twin—the company provides enterprises with full-chain services from water quality diagnosis and process optimization to intelligent operations, helping customers improve water reuse rates and reduce operating costs.

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