Frequently asked questions

Nereda technology is an innovative biological wastewater treatment technology, based on the unique characteristics of a special type of biomass or ‘activated sludge’. Nereda technology purifies water using the unique features of ‘aerobic granular biomass”. Contrary to conventional processes, the purifying bacteria concentrate naturally in compact granules, with superb settling properties. Furthermore a large variety of biological processes take place simultaneously in such granules. Nereda technology provides excellent water quality through compact and easy to operate installations, at low energy consumption. Nereda technology is cost-effective and is applied in new and upgrades of municipal and industrial wastewater treatment facilities.

The name Nereda derives from the Greek word “Neraida”. Nereda was a water nymph and one of the daughters of Nereus, the wise and benevolent Greek god of the sea. In Greek mythology Nereda is linked with the terms “pure” and “immaculate”, a hint to the water quality produced by the new technology.

The advantages of Nereda technology are compelling and could be categorized in four main benefits:

• Cost-effective
• Small footprint
• Easy-to-operate
• Sustainable

Compared to conventional biological nutrient removal activated sludge processes with clarifiers, savings on footprint can be up to 75%. Compared to conventional SBR’s saving on footprint is approx. 50%, thanks to the optimized cycle and the higher biomass concentration (MLSS).

Compared to conventional activated sludge systems Nereda technology is significantly more energy efficient as it requires a lower amount of mechanical equipment. (e.g. Nereda technology does not require return sludge pumps, mixers in anaerobic tanks, mixers in selector tanks, propulsion in activated sludge reactors). The energy savings are often in the range of 20-30%. On top of that, additional energy savings are expected as a result of a higher than normal aeration efficiency.

Considerations for odour control in Nereda technology are not much different than for conventional activated sludge processes.Wastewater contains volatile components that may be malodourous. For that reason, and depending on permitted or desired odour emission, a wastewater treatment plant (WWTP) is equipped with odour abatement measures. The main sources of odour are the raw wastewater and the processing of the imported and on-site generated biosolids. Therefore, adequate covering and treatment of the emitted air is typically applied for e.g. the inlet works, screening, degritter, sludge thickening, digestion, sludge dewatering and sludge storage. Note that primary clarifiers can also be a significant source of a plant’s odour emission. Covering primary clarifiers is not only relatively expensive but associated air treatment can also be power intensive. As emissions from the biological treatment section is relatively limited, there is, even in urban and residential environment, typically no need for covering and air treatment.Experience shows that odour emission from the Nereda process is similar to that of conventional activated sludge plants. This is also illustrated by the fact that several of the WWTPs that use Nereda technology comply with very stringent odour emission targets and meet those without covering the biological Nereda reactor and subsequent odour treatment. In addition, the fact that a Nereda-based WWTP can achieve a low power consumption without using primary clarifier can be an advantage in designing cost-effective zero-nuisance WWTP’s.

Nereda technology results in construction costs that are lower than for conventional technology, which is understandable, because the plant footprint is up to a factor 4 smaller, tank volumes are smaller and less equipment will be required. The investment savings are however very site specific and thus will vary per project, which makes it difficult to give a generalized answer. The investment savings are significant.

Operating costs are significantly lower as result of:

• lower energy consumption
• less equipment and its maintenance
• no chemicals needed for P-removal / no chemical waste produced
• surplus sludge production is comparable to conventional activated sludge systems, but, as is the case with anaerobic granular sludge, surplus sludge could be sold for start-up of other units. Anaerobic granules in early days of UASB plant start-ups were called “the black gold”.

NNOP is the National Nereda Research Program, a cooperation between Royal HaskoningDHV, the Dutch Foundation for Applied Water Research (STOWA), Delft University of Technology (TUD) and six Dutch water boards. As part of the NNOP several extensive municipal pilot projects were executed. The NNOP worked on the research and development Nereda over a 20-year period. The original invention of aerobic granular biomass was made at the Delft University of Technology. The invention moved from the laboratory to real-life application to pilot installations, and culminated in the opening of the world’s first operational municipal plant in the Dutch town of Epe in 2012.

The Nereda Controller is a smart, integrated process controller for Nereda. The controller not only ensures fully automated plant operation, reliable performance and ease-of-operation but also optimized and energy-efficient treatment.

There are several differences:

Compact: Nereda technology is at least as compact as a MBR but will show much lower investment and operating costs

Virtually no suspended soils: due to the membranes, MBR will virtually have no suspended solids in the effluent. The suspended solids concentration in the effluent of Nereda without polishing step will be comparable to a normal activated sludge system (and is thus higher than MBR). However by applying simple screens or filters, the suspended solids in the Nereda effluent can be easily removed down to very low concentrations and thus effluent quality for base parameters like SS, P, COD and N will be comparable to those of MBR.

No microfiltration: MBR applies microfiltration or ultra filtration membranes. Due to theses membranes also a part of bacteria and viruses are removed from the water. Without a similar polishing step, Nereda technology is expected to have bacteria/viruses in the effluent similar to normal activated sludge systems.

Reusage: MBR is often used if water reuse is required. Similarly, Nereda effluent from municipal Nereda plants can be reused for irrigation.

Yes, like conventional systems the effluent can be reused. The biological process ensures a strong reduction in organics, harmful bacteria and if targeted: nutrients as well. Similar to conventional treatment the effluent will contain some suspended solids, which can be easily removed if so required. Advantage is that relative easily filtration seems to be possible, but also membrane filtration (like in MBR) would be an available option. For example the effluent from the Gansbaai plant is reused for greening and irrigation after pond sedimentation.