Aerobic granulation

The biological treatment of wastewater in the sewage treatment plant is often accomplished using conventional activated sludge systems. These systems generally require large surface areas for treatment and biomass separation units due to the generally poor settling properties of the sludge. In recent years, new technologies have been developed to improve settlability. The use of aerobic granular sludge technology is one of them.

Aerobic Granules derived from municipal sewage AGS application
Aerobic Granules

Context

Proponents of aerobic granular sludge technology claim "it will play an important role as an innovative technology alternative to the present activated sludge process in industrial and municipal wastewater treatment in the near future"[1] and that it "can be readily established and profitably used in activated sludge plants".[2] However in 2011 it was characterised as "not yet established as a large-scale application ... with limited and unpublished full-scale applications for municipal wastewater treatment."[3]

Aerobic granular biomass

The following definition differentiates an aerobic granule from a simple floc with relatively good settling properties and came out of discussions which took place at the “1st IWA-Workshop Aerobic Granular Sludge” in Munich (2004):[2]

“Granules making up aerobic granular activated sludge are to be understood as aggregates of microbial origin, which do not coagulate under reduced hydrodynamic shear, and which settle significantly faster than activated sludge flocs”(de Kreuk et al. 2005[4])"

Formation of aerobic granules

SBR Reactor, with aerobic granules

Granular sludge biomass is developed in sequencing batch reactors (SBR) and without carrier materials. These systems fulfil most of the requirements for their formation as:

Feast - Famine regime: short feeding periods must be selected to create feast and famine periods (Beun et al. 1999[5]), characterized by the presence or absence of organic matter in the liquid media, respectively. With this feeding strategy the selection of the appropriate micro-organisms to form granules is achieved. When the substrate concentration in the bulk liquid is high, the granule-former organisms can store the organic matter in form of poly-β-hydroxybutyrate to be consumed in the famine period, giving an advantage over filamentous organisms. When an anaerobic feeding is applied this factor is enhanced, minimising the importance of short settling time and higher hydrodynamic forces.
Short settling time: This hydraulic selection pressure on the microbial community allows the retention granular biomass inside the reactor while flocculent biomass is washed-out. (Qin et al. 2004[6])
Hydrodynamic shear force : Evidences show that the application of high shear forces favours the formation of aerobic granules and the physical granule integrity. It was found that aerobic granules could be formed only above a threshold shear force value in terms of superficial upflow air velocity above 1.2 cm/s in a column SBR, and more regular, rounder, and more compact aerobic granules were developed at high hydrodynamic shear forces (Tay et al., 2001[7] ).

Granular activated sludge is also developed in flow-through reactors using the Hybrid Activated Sludge (HYBACS®) process,[8] comprising an attached-growth reactor with short retention time upstream of a suspended growth reactor. The attached bacteria in the first reactor, known as a SMART unit, are exposed to a constant high COD, triggering the expression of high concentrations of hydrolytic enzymes in the EPS layer around the bacteria. The accelerated hydrolysis liberates soluble readily-degradable COD which promotes the formation of granular activated sludge.

Advantages

The development of biomass in the form of aerobic granules is being studied for its application in the removal of organic matter, nitrogen and phosphorus compounds from wastewater. Aerobic granules in an aerobic SBR present several advantages compared to conventional activated sludge process such as:

Stability and flexibility: the SBR system can be adapted to fluctuating conditions with the ability to withstand shock and toxic loadings
Low energy requirements: the aerobic granular sludge process has a higher aeration efficiency due to operation at increased height, while there are neither return sludge or nitrate recycle streams nor mixing and propulsion requirements
Reduced footprint: The increase in biomass concentration that is possible because of the high settling velocity of the aerobic sludge granules and the absence of a final settler result in a significant reduction in the required footprint.
Good biomass retention: higher biomass concentrations inside the reactor can be achieved, and higher substrate loading rates can be treated.
Presence of aerobic and anoxic zones inside the granules: to perform simultaneously different biological processes in the same system (Beun et al.. 1999[5] )
Reduced investment and operational costs: the cost of running a wastewater treatment plant working with aerobic granular sludge can be reduced by at least 20% and space requirements can be reduced by as much as 75% (de Kreuk et al.., 2004[9]).

The HYBACS process has the additional benefit of being a flow-through process, thus avoiding the complexities of SBR systems. It is also readily applied to the upgrading of existing flow-through activated sludge processes, by installing the attached growth reactors upstream of the aeration tank. Upgrading to granular activated sludge process enables the capacity of an existing wastewater treatment plant to be doubled.[10]

Treatment of industrial wastewater

Synthetic wastewater was used in most of the works carried out with aerobic granules. These works were mainly focussed on the study of granules formation, stability and nutrient removal efficiencies under different operational conditions and their potential use to remove toxic compounds. The potential of this technology to treat industrial wastewater is under study, some of the results:

Pilot research in aerobic granular sludge

Aerobic granulation technology for the application in wastewater treatment is widely developed at laboratory scales. The large-scale experience is growing rapidly and multiple institutions are making efforts to improve this technology:

The feasibility study showed that the aerobic granular sludge technology seems very promising (de Bruin et al., 2004.[20] Based on total annual costs a GSBR (Granular sludge sequencing batch reactors) with pre-treatment and a GSBR with post-treatment proves to be more attractive than the reference activated sludge alternatives (6-16%). A sensitivity analysis shows that the GSBR technology is less sensitive to land price and more sensitive to rain water flow. Because of the high allowable volumetric load the footprint of the GSBR variants is only 25% compared to the references. However, the GSBR with only primary treatment cannot meet the present effluent standards for municipal wastewater, mainly because of exceeding the suspended solids effluent standard caused by washout of not well settleable biomass.

Full scale application

Aerobic granulation technology is already successfully applied for treatment of wastewater.

Full-scale municipal sewage Nereda application (4000 m3.d-1) at the Gansbaai STP in South Africa
Full-scale municipal sewage Nereda application Epe the Netherlands
Full-scale industrial sewage Nereda application Vika the Netherlands

See also

References

  1. Ni, Bing-Jie (2013). Formation, Characterization and Mathematical Modeling of the Aerobic Granular Sludge (PDF). Springer. ISBN 978-3-642-31280-9.
  2. 1 2 Bathe, Stephan (2005). Aerobic granular sludge : selected proceedings of the 1st IWA-workshop aerobic granular sludge organised by the Institute of water quality control and waste management of the technical University of Munich (TUM) in cooperation with the Institute of advanced studies on sustainability of the European Academy of sciences and arts (EASA) and the international water association (IWA) (1. ed.). Londen: IWA publishing. ISBN 978-1843395096.
  3. Gao, Dawen; Liu, Lin; Liang, Hong; Wu, Wei-Min (1 June 2011). "Aerobic granular sludge: characterization, mechanism of granulation and application to wastewater treatment" (PDF). Critical Reviews in Biotechnology. 31 (2): 137–152. doi:10.3109/07388551.2010.497961. Retrieved 11 December 2012.
  4. de Kreuk M.K., McSwain B.S., Bathe S., Tay S.T.L., Schwarzenbeck and Wilderer P.A. (2005). Discussion outcomes. Ede. In: Aerobic Granular Sludge. Water and Environmental Management Series. IWA Publishing. Munich, pp.165-169)
  5. 1 2 Beun J.J., Hendriks A., Van Loosdrecht M.C.M., Morgenroth E., Wilderer P.A. and Heijnen J.J. (1999). Aerobic granulation in a sequencing batch reactor. Water Research, Vol. 33, No. 10, pp. 2283–2290.
  6. Qin L. Liu Y. and Tay J-H (2004). Effect of settling time on aerobic granulation in sequencing batch reactor. Biochemical Engineering Journal, Vol. 21, No. 1, pp. 47–52.
  7. Tay J.-H., Liu Q.-S. and Liu Y. (2001). The effects of shear force on the formation, structure and metabolism of aerobic granules. Applied Microbiology and Biotechnology, Vol. 57, Nos. 1–2, pp. 227–233.
  8. "Archived copy". Archived from the original on 2015-08-28. Retrieved 2015-09-03.
  9. de Kreuk, M.K., Bruin L.M.M. and van Loosdrecht M.C.M. (2004). Aerobic granular sludge: From idea to pilot plant.. In Wilderer, P.A. (Ed.), Granules 2004. IWA workshop Aerobic Granular Sludge, Technical University of Munich, 26–28 September 2004 (pp. 1–12). London: IWA.
  10. "Archived copy" (PDF). Archived from the original (PDF) on 2015-05-14. Retrieved 2015-09-03.
  11. Arrojo B., Mosquera-Corral A., Garrido J.M. and Méndez R. (2004) Aerobic granulation with industrial wastewater in sequencing batch reactors. Water Research, Vol. 38, Nos. 14-15, pp. 3389 – 3399
  12. Schwarzenbeck N., Erley R. and Wilderer P.A. (2004). Aerobic granular sludge in an SBR-system treating wastewater rich in particulate matter. Water Science and Technology, Vol. 49, Nos. 11-12, pp. 41–46.
  13. Cassidy D.P. and Belia E. (2005). Nitrogen and phosphorus removal from an abattoir wastewater in a SBR with aerobic granular sludge. Water Research, Vol. 39, No. 19, pp. 4817–4823.
  14. Inizan M., Freval A., Cigana J. and Meinhold J. (2005). Aerobic granulation in a sequencing batch reactor (SBR) for industrial wastewater treatment. Water Science and Technology, Vol. 52, Nos. 10-11, pp. 335–343.
  15. Tsuneda S., Ogiwara M., Ejiri Y. and Hirata A. (2006). High-rate nitrification using aerobic granular sludge. Water Science and Technology, 53 (3), 147-154.
  16. Shams Qamar Usmani, Suhail Sabir, Izharul Haq Farooqui and Anees Ahmad (2008) Biodegradation of Phenols and p-Cresol by Sequential Batch Reactor proc. International Conference on Environmental Research and Technology (ICERT 2008), scope 10, pp 906–910, ISBN 978-983-3986-29-3.
  17. Figueroa M., Mosquera-Corral A., Campos J. L. and Méndez R. (2008). Treatment of saline wastewater in SBR aerobic granular reactors. Water Science and Technology, 58 (2), 479-485.
  18. Farooqi I.H., Basheer F. and Ahmad T.(2008). Studies on Biodegradation of Phenols and m -Cresols by Upflow Anaerobic Sludge Blanket and Aerobic Sequential Batch Reactor.Global Nest Journal,10(1), 39-46.
  19. López–Palau S., Dosta J. and Mata-Álvarez J. (2009). Start-up of an aerobic granular sequencing batch reactor for the treatment of winery wastewater. Water Science and Technology, 60 (4), 1049-1054.
  20. de Bruin L.M.M., de Kreuk M.K., van der Roest H.F.R., Uijterlinde C. and van Loosdrecht M.C.M. (2004). Aerobic granular sludge technology: and alternative to activated sludge. Water Science and Technology, Vol. 49, Nos. 11-12, pp. 1–7)

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