NEREDA^®: an emerging technology for sewage treatment

Several modification of conventional activated sludge process (ASP) were made for efficient removal of carbon, nitrogen and phosphorous since its development. The problem of poor settling of sludge, high bulking and low nutrient removal frequently experienced in ASP systems. This has led to the development of advanced biological nutrient removal (BNR) systems for activated sludge. Several options are available these days such as sequencing batch reactor (SBR), moving bed bio-film reactor (MBBR), continuous fill intermittent decant type SBR, down flow hanging sponge (DHS) reactor and rotating biological contactors (RBC) (Khan 2012). SBR and MBBR were now used at full scale level while DHS and RBC under laboratory/pilot scale investigation. Results are promising; however, more studies are needed at pilot scale or demonstration level with actual environmental conditions (Khan et al. 2011). The most common problem encountered in the operation of these modified ASP system are foaming and bulking. The mixed liquor suspended solid (MLSS) flocs do not settle well or compact and flocs discharged in effluent in a bulking sludge.

Prof. Mark van Loosdrecht (2012 Lee Kuan Yew Water Prize winner), and his team at Delft University of Technology (TU Delft) investigated the formation of aerobic granules 1990s (Morgenroth et al. 1997; De Kreuk 2006; De Kreuk et al. 2007). The SBR is one of the modifications of ASP which can utilize on aerobic granular biomass to get rid of poor settling and bulking and sufficient number of pilots scale plants were installed for municipal and industrial wastewater (Khan 2012). Aerobic granular biomass has several advantages over conventional activated sludge flocs that have been well-documented. These include good settling ability that leads to better biomass retention and higher biomass concentrations, provision of a structured matrix for biomass growth, and ability to withstand high load variations (De Kreuk et al. 2010). These all lead to a compact reactor design that can reduce plant footprints significantly. Recently, the process has been engineered to suit commercial applications by DHV (now known as Royal HaskoningDHV) and has been commercially branded as Nereda^® Technology.

Nereda, a new biological wastewater technology, has been deployed at number of municipal waste water treatment plant (WWTP) in The Netherlands, to meet the high standards of sludge treatment, chemicals use and energy consumption. During 2007, six Dutch Water Boards, Technical University, Delft, STOWA (Dutch Foundation for Applied Water Research) and Royal HaskoningDHV jointly agreed to scale-up and implement aerobic granular biomass technology (NEREDA) for municipal applications.

Following the successful operation of Gansbaai (South Africa) plant, more than 20 other municipal Nereda^® plants are under construction and technology grew-out from an innovation into a proven new standard for urban and industrial biological wastewater treatment. Recently Royal HaskoningDHV has been awarded the first two of the (at least) ten planned Nereda^® installations for a design capacity of 517,000PE (57,024 m³/day) in Limeira (Tatu) and for 480,000 p.e. (86,400 m³/day) in Rio de Janeiro (Deodoro) in Brazil.

The first full-scale Nereda^® was installed during 2005 in a cheese industry in The Netherlands by retrofitting a milk storage tank into a treatment tank for inflow of 250 m³/day. Later during 2008, NEREDA was scaled-up for municipal applications at Gansbaai sewage treatment plant (STP), South Africa.

During a cyclic operation of the NEREDA, 3 h cycle time was applied to promote the adaptation of the microorganisms to the wastewater. Table 1 shows the physico-chemical parameters of the NEREDA plant at Gansbaai. In fact, NEREDA at Gansbaai (South Africa) WWTP was the first demonstration installation for treatment of sewage. The treatment plant was designed for 5,000 m³/day for high strength municipal wastewater. Final effluent quality was expected to follow the effluent discharge limits. Result indicates a remarkable high performance of the WWTP (Table 1). Final treated effluent was reused for irrigation, after disinfection. Various parameters of the Nereda regarding the removal of organic matter, nitrogen and phosphorous are presented in Table 1. The NEREDA was operated on the 3 h batch cycle and stable performance was observed. The values obtained for the NEREDA presented insignificant variations in COD, SS, nitrogen and phosphorous removal thus indicating that the NEREDA system was stable. The overall removal rate of organic matter, SS and ammonia nitrogen carried by the NEREDA was 97, 99% and 90% respectively.

The Epe WWTP, using the Nereda wastewater technology, which flows up to 1,500 m³ per hour, was commissioned in the middle of 2011. The plant was designed to meet the high influent COD load at temperature ranged 8–25 °C. The plant, which has been operational for the last 16 months, has been under constant monitoring for its performance.

During the monitoring, the Nereda wastewater technology exceeded its expectations and met the set stringent standards of effluent quality, sludge treatment, chemical use and power consumption. Electricity required by the plant, including sand filtration and sludge treatment, is comparatively less than that of any other similarly sized conventional treatment plant in the country. In addition, the system's effluent quality meets the country's set standards, which specifies that total nitrogen and phosphorous concentrations should be less than 5 and 0.3 mg per litre. Nereda is cost-effective and can save over 25% in investment and operational costs, when compared to other conventional systems. The system, which showed endurance and stability under strong varying influent load conditions and extreme influent pH fluctuations, can also remove Nitrogen from sludge even in wintry conditions.

The high quality effluent could be obtained from Nereda treatment. Results of Epe WWTP were summarized in Table 2. Results are summarized based on composite sample analysis. No adverse effect was observed in the treatment performance of plant since large fluctuations in the influent hydraulic and organic load particularly with pH frequently rises up to 10 occurred due to mixing of industrial waste. During pilot studies, the remarkable stability was noticed. Occasionally, Nereda^® pilot unit receiving the same influent observed insignificant disturbance but resumed smooth operation after a few cycles and was back to normal operation in 1–2 days after the occurrence of adverse effect of high pH.

The primary advantage of Nereda^® technology was less power requirement. Since at Epe, original plant based on ASP was utilizing 3,500 kWh/d energy while with Nereda^®, the average daily consumption is 2,000 kWh–2,500 kWh for same treatment capacity. This is a reduction of approximately 40% energy. Results on energy use were further supported by the demonstration plant at Frielas WWTP, Portugal.

The Frielas WWTP is designed for 70,000 m³/d capacity. Presently conventional ASP based WWTP was receiving about 70% of its biological design capacity sewage from 250,000 inhabitants, from the Greater Lisbon area. Since the start-up of plant during 1997, the Frielas WWTP suffered several operational constraints related to process design and wastewater characteristics as it became quite different from those used for the original plant design.

An important driving force of implementing the Nereda^® was the possibility of working at higher hydraulic loads and achieving nutrient removal without the need for increasing reactor volume. Besides providing a robust and efficient operation during all influent conditions, a driver for the retrofit was to evaluate the possibility to substantially lower the electricity demand of a conventional WWTP.

The demonstration scale Nereda reactor was started-up with normal activated sludge obtained from one of the aeration basin. After successful start-up, a steady state conditions were reached and a SVI30 around 40 mL/g, a SVI5 as low as 60 mL/g, a granulation fraction above 80% and an increasing biomass concentration in the range of 6 to 8 g/L was observed.

During start-up, the slower biomass growth and transformation rate was observed as this WWTP since the Nereda reactor was started partially during winter time with diluted wastewater (i.e. COD levels below 300 mg/L). Significantly good effluent quality was observed after more than one year of plant operation and far more consistent than the quality obtained in the original continuous AS system.

Results revealed that the average specific consumption for the Nereda^® amounts to 0.35 kWh/kg COD removed, representing approximately 30% electricity savings compared to aeration for the AS system. Combining this with the energy saving that granules bring by not using settling tanks, sludge recirculation pumps and post-filtration units, the overall electricity saving potential for the plant was computed to 50%.

Based on the commendable plant performance and results obtained with the Nereda^® demonstration reactor, Royal HaskoningDHV has commissioned and implement an extension of the demonstration to a full-scale reactor. The plant is about to start during late 2014. The reactor will have a treatment capacity of 12,000 m³/d and 40,000 inhabitants. After upgrade the Frielas WWTP will be able to meet the current discharge requirements.

Initially plant was primarily seeded with activated sludge obtained from an extended aeration system. The inflow was gradually increased to design flow within approx. 3 months. Since start-up the nitrogen removal was almost instantaneous meeting the discharge, while extensive biological phosphate removal developed over the three month period.

The final effluent quality was following the disposal standards criteria and final conc. were well below the target of TN <7 mg/L and TP < 1 mg/L.

The energy consumption of both the Nereda^® and the conventional system is closely monitored and shows that the Nereda treatment line is 50–60% more energy efficient.

The results were observed quite interesting in terms of organics, SS, nitrogen and phosphorous removal at demonstration and full scale application of NEREDA technology for sewage treatment. Further, a comparison of energy consumption was made at two WWTP between Nereda and conventional ASP system and found that approximately 40% energy reduction could be achieved by Nereda technology. Moreover, compact and high conc. of granular biomass could be useful to reduce the foot print area up to 75 and 50% with conventional ASP and SBR. For the last two decades, the Nereda^® technology has been scaled-up and developed from laboratory, pilot and demo into a dozen full scale applications. Enormous data from these municipal demo applications show that BNR in combination with high energy-efficiency and cost-effective plant construction are obtained.

The authors gratefully acknowledge the support of Prof. M.C.M Van Loosdrecht and Royal HaskoningDHV B.V. during writing this manuscript.