Aerobic Granular Sludge Becomes the Standard in Europe
A New Generation After Activated Sludge
Aerobic granular sludge (AGS) is a new biological treatment approach replacing conventional activated sludge systems and has spread rapidly worldwide over the last five years. Developed in the Netherlands and commercialised under the "Nereda" brand, the technology is now operating in over 100 full-scale plants across more than 80 countries.
Why Is It Growing So Fast
The advantages of AGS over conventional activated sludge are striking on both technical and economic grounds:
- Plant footprint reduction up to 75 percent
- 30 percent decrease in energy consumption
- Simultaneous nitrogen and phosphorus removal (without additional dosing)
- No need for a secondary settling tank
- Reduced sludge volume and improved dewatering performance
These features become decisive especially for plants facing land constraints in urban areas.
How the Technology Works
AGS is based on a biological process where microorganisms grow in dense granules instead of flocs. Sequential phases (in SBR logic) within a single tank create aerobic, anoxic and anaerobic conditions, allowing different pollutant removal mechanisms to take place in the same reactor. The granular structure provides high density and rapid settling.
Comparison Table
A typical comparison between activated sludge and AGS in an urban wastewater plant:
- Hydraulic retention time: 12 hours / 6 hours
- Specific energy consumption: 0.45 kWh/m³ / 0.30 kWh/m³
- Sludge age: 15–25 days / 25–40 days
- Sludge volume index (SVI): 100–150 mL/g / 35–65 mL/g
- Total plant area: reference / 25–35 percent of reference
Deployments in Turkey
In Turkey, the technology is still in an early diffusion phase. A few mid-size pilot plants have been built through partnerships between the Dutch licensor and local engineering firms. Feasibility studies are underway in Ankara, Izmir and Antalya, while retrofit scenarios for converting existing plants to AGS are also on the agenda. The Ministry of Environment is preparing a technical guideline to make AGS comparison a standard step in new plant design.
Licensing and Patent Dimension
A key constraint of the technology is the concentration of patent and licensing rights with a single provider. This produces a license fee that offsets some of the cost advantage. That said, a significant portion of the core patents will expire in the next three years, paving the way for new players in the market and price competition.
Implications for the Sector
For EPC firms, AGS is becoming a required capability in the engineering portfolio. For operators, training investment to adapt existing operating know-how to this new technology matters too. Over the next decade, a significant share of urban wastewater investments in Europe is expected to be AGS-based designs.