Scientific Summary: Anaerobic Sludge Granulation Under Saline Conditions

A variety of industries are generating saline wastewaters (e.g., agro-food, leather oil and gas industries ), which would have a negative impact on aquatic life and agriculture, if discharged without prior treatment. The application of biological treatment to remove organic pollutants from these wastes is somewhat limited due to salt (mainly NaCl) toxicity [1]. Two fundamental strategies are known for cells to survive under osmotic stress:

  • Increase of intracellular ion concentration, namely potassium;
  • Uptake or synthesis of osmolites.

The second strategy does not require adaptation of cell’s enzyme machinery and is common in most prokaryotes [2], [3].

The most widely used anaerobic wastewater treatment systems for industrial high strength effluents are upflow anaerobic sludge blankets (UASBs). Performance of these systems strongly depends on bio-aggregate’s (granule) formation, when treating wastewater with mainly dissolved COD and a limited amount of solids [4], [5]. Even though bio-aggregation is commonly encountered in biological wastewater treatment systems, the mechanisms behind it are still unclear and based on hypothesis [6].

In a recent review I. Vyrides [7] states, that biological treatment of highly saline wastewaters is necessary and can be economically viable and concludes, that application of compatible solutes to overcome salinity stress is still in early stages of studies. Moreover, there is a lack of strategies to cope with varying salinities within biological treatment systems as they occur in industries [7].

The objective of this study is developing strategies to cope with high salinity in UASB reactors as well as studying mechanisms of granulation under saline conditions, thus addressing two fundamental questions for biological process application to be extended to highly saline wastewaters.




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  2. Roeßler, M. and V. Müller, Osmoadaptation in bacteria and archaea: common principles and differences. Environmental microbiology, 2001. 3(12): p. 743-754.
  3. Gunde-Cimerman, N., A. Oren, and A. Plemenitaš, Adaptation to life at high salt concentrations in Archaea, Bacteria, and Eukarya. Vol. 9. 2006: Springer Science & Business Media.
  4. Hulshoff Pol, L., The phenomenon of granulation of anaerobic sludge. 1989, Landbouwuniversiteit te Wageningen.
  5. Pol, L.H., et al., Anaerobic sludge granulation. Water Research, 2004. 38(6): p. 1376-1389.
  6. Ding, Z., et al., Role of extracellular polymeric substances (EPS) production in bioaggregation: application to wastewater treatment. Applied microbiology and biotechnology, 2015: p. 1-23.
  7. Vyrides, I., Anaerobic Treatment of Organic Saline Waste/Wastewater: Overcome Salinity Inhibition by Addition of Compatible Solutes, in Environmental Microbial Biotechnology. 2015, Springer. p. 105-117.