Abstract

When aerobic granular sludge is applied for industrial wastewater treatment, different soluble substrates can be present. For stable granular sludge formation on volatile fatty acids (e.g. acetate), production of storage polymers under anaerobic feeding conditions has been shown to be important. This prevents direct aerobic growth on readily available chemical oxygen demand (COD), which is thought to result in unstable granule formation. Here, we investigate the impact of acetate, methanol, butanol, propanol, propionaldehyde, and valeraldehyde on granular sludge formation at 35 °C. Methanogenic archaea, growing on methanol, were present in the aerobic granular sludge system. Methanol was completely converted to methane and carbon dioxide by the methanogenic archaeum Methanomethylovorans uponensis during the 1-h anaerobic feeding period, despite the relative high dissolved oxygen concentration (3.5 mg O2 L−1) during the subsequent 2-h aeration period. Propionaldehyde and valeraldehyde were fully disproportionated anaerobically into their corresponding carboxylic acids and alcohols. The organic acids produced were converted to storage polymers, while the alcohols (produced and from influent) were absorbed onto the granular sludge matrix and converted aerobically. Our observations show that easy biodegradable substrates not converted anaerobically into storage polymers could lead to unstable granular sludge formation. However, when the easy biodegradable COD is absorbed in the granules and/or when the substrate is converted by relatively slow growing bacteria in the aerobic period, stable granulation can occur.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-014-6358-3) contains supplementary material, which is available to authorized users.

Highlights

  • Aerobic granular sludge (AGS) is an innovative technology to simultaneously remove nitrogen, phosphorus and carbon from wastewater with bacterial granules

  • We studied the conversion and evaluated the granulation potential of a set of carbon compounds frequently encountered in industrial wastewaters, i.e. acetate, methanol, butanol, propanol, propionaldehyde and valeraldehyde

  • This was gradually decreased by 3–5 min over the course of 3 weeks to a final 3-min settling time corresponding to a minimum settling velocity of 12 m h−1

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Summary

Introduction

Aerobic granular sludge (AGS) is an innovative technology to simultaneously remove nitrogen, phosphorus and carbon from wastewater with bacterial granules. This is achieved in one reactor compartment; the requirement of space and energy is highly reduced (De Kreuk and van Loosdrecht 2006b). Full scale aerobic granular reactors treating domestic wastewater are currently operational in The Netherlands, Portugal and South Africa (Giesen et al 2013). AGS is formed by applying selective environmental pressures on bacteria generally found in sewage treatment sludge (Beun et al 2000; McSwain et al 2004). When all soluble COD is removed, the bacteria are supplied with oxygen (and nitrate), and they

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