Industry News
2026-10-15The board of directors of the Spanish state-owned water utility ACUAES approved the signing of an agreement to advance the upgrade of the Cartagena Mar Menor Sur wastewater treatment plant, with a total investment of 1500万 euros. The core is a new tertiary treatment system, with an average flow of 3.5万 m³/day and a maximum of 5万 m³/day, adopting an equalization tank plus deep-bed filtration + UV disinfection process, and the effluent must meet Spain's Class A agricultural standard for direct supply to irrigation users.
I. From Lagoon Crisis to a 6.75亿 Euro Action Framework
Mar Menor is one of Europe's largest saltwater lagoons. For many years, repeated algal blooms and hypoxia events caused by eutrophication have kept its ecological condition in the spotlight. Among the various stressors, sewage management has been explicitly identified as one of the key pressures; the relevant region is also drafting new coastal discharge control regulations, further tightening the requirements.
This upgrade is part of the "Priority Action Framework for the Restoration of Mar Menor," which is supported by 6.75亿 euros from Spain's Ministry for Ecological Transition. This means the Mar Menor Sur project is not an isolated plant-level retrofit, but an execution unit within a basin governance investment package — this organizational approach of "framework first, projects implemented in batches" has been a common practice in European water environment governance in recent years.
II. Process Configuration: Equalization Tank + Deep-Bed Filtration + UV Disinfection
The core of the project is a new tertiary treatment system, designed for an average flow of 3.5万 m³/day and a maximum of 5万 m³/day. The process comprises:
- Equalization tank — buffers fluctuations in influent volume and quality, providing stable hydraulic conditions for the downstream filtration unit, and is key to coping with wet-weather shock loads and water intake fluctuations during the irrigation season.
- Deep-bed filtration — further removes Suspended Solids and particulate pollutants from the secondary effluent, creating favorable conditions for disinfection. The filtered turbidity directly determines the actual dose efficiency of UV disinfection.
- UV disinfection — achieves microbial inactivation without dosing chemicals, avoiding the adverse effects of residual chlorine on irrigated crops and soil microorganisms.
The tertiary treatment system is built above the existing primary treatment section (rehabilitated existing structures). This approach saves a substantial amount of new land, and is an idea worth referencing when expanding existing plants.
In addition to the main process, the project also includes replacing aging electromechanical equipment, improving the aeration system of the biological treatment, adding generators, and installing sound barriers along part of the plant boundary. These items may appear ancillary, but they actually correspond respectively to operational reliability, energy consumption, power supply resilience, and neighbor relations — the parts that are often cut during old plant retrofits yet most prone to problems.
III. Class A: The Water Quality Threshold for Direct Supply of Reclaimed Water to Irrigation Users
The project explicitly requires that the Reclaimed Water produced must meet the Class A agricultural standard under current Spanish regulations, so that it can be supplied directly to local irrigation users.
The standard design of Reclaimed Water Reuse for agriculture typically addresses three categories of risk: microbial (pathogens and parasite eggs), chemical pollutants (heavy metals, persistent organic compounds, salinity), and sensory and operational indicators (turbidity, odor). Class A, as a higher grade, generally corresponds to stricter microbial indicators and more complete treatment process requirements, while also imposing limits on irrigation methods, crop types, and exposed populations.
For the project, this brings two practical constraints: first, the effluent quality must meet standards continuously and stably, not merely on spot-check basis, so process redundancy and online monitoring configuration cannot be omitted; second, the reliability of water supply must match the irrigation season — agricultural water demand is concentrated in specific months, and the treatment system needs to withstand seasonal load fluctuations.
IV. Funding Structure: Half EU Funds, Half 30年 Water Tariff Recovery
The project's financing arrangement deserves separate mention:
- 50% comes from the European Regional Development Fund (ERDF) within the 2021—2027 period.
- Another 50% is advanced by ACUAES from its own reserves, and then gradually recovered through ESAMUR via water tariffs over a 30年 period.
- The Cartagena municipal government provides the land and assumes responsibility for the plant's subsequent operation and maintenance.
This structure extends the recovery period of construction costs to a scale matching the plant's service life, thereby avoiding the political resistance of a one-time significant water price increase. The combination of grants and long-term recovery funds is also a leverage approach commonly used by the EU in the water environment infrastructure sector: grants lower the project threshold, while recovery funds form a recyclable funding pool.
It should be noted that the formal construction tender can only be launched after the tripartite agreement is signed. In other words, the project is currently at the approval advancement stage and has not yet entered construction implementation.
V. Reference for Agricultural Use of Reclaimed Water in China
The use of reclaimed water for agricultural irrigation is also considerable in scale in China, especially in water-scarce areas in the north and around large irrigation districts. From Spain's practice, three points of experience have reference value:
- Standards should be tiered, and uses should correspond—setting different grades according to crop types and exposed populations is more feasible than a uniform high standard, and can also avoid the waste caused by using high-quality reclaimed water in low-requirement scenarios.
- Treatment processes should match the reuse season—equalization tanks and redundancy design are not optional; the centralized water intake characteristics of agricultural irrigation determine that the system's peak response capacity must be considered in advance.
- Long-term funding arrangements determine whether a project can be implemented—the water fee recovery mechanism of 30年 essentially aligns infrastructure investment with user payment along the time dimension. Such designs are particularly critical for water environment projects with large investment scale and limited direct returns.
From a broader perspective, the Mar Menor Sur project reflects the mature approach of European water environment governance: deriving project investment from watershed goals, leveraging EU funds to drive local implementation, and opening market outlets for reclaimed water through clear water quality grades. When reclaimed water is truly accepted by irrigators as a stable water source, the role of wastewater treatment plants also shifts from end-of-pipe treatment facilities to a component of the regional water supply system.
TIANYI TECH Co., Ltd. (TIANYI LIMITED) has long been deeply engaged in the fields of wastewater treatment and reclaimed water reuse. Centering on three major directions—low-carbon processes, resource recovery, and smart operations—it provides full-chain services from scheme design, equipment manufacturing, engineering construction, to operation management for municipal wastewater treatment plants, industrial parks, and various water-using entities. With the goals of "stable compliance, energy saving and consumption reduction, and resource circulation," the company continuously helps customers reduce operating costs and enhance system resilience in the green and low-carbon transition.
Source: Public information from the Spanish water authority ACUAES regarding the Mar Menor Sur wastewater treatment plant upgrade agreement, compiled from public reports such as Spanish News Today (early 2026年10月).
