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. 2016 Apr 2;46(7):635-672.
doi: 10.1080/10643389.2016.1149903. Epub 2016 Feb 18.

Nonoxidative removal of organics in the activated sludge process

Oskar Modin  1 , Frank Persson  1 , Britt-Marie Wilén  1 , Malte Hermansson  2
Affiliations

Nonoxidative removal of organics in the activated sludge process

Oskar Modin et al. Crit Rev Environ Sci Technol. .

Abstract

The activated sludge process is commonly used to treat wastewater by aerobic oxidation of organic pollutants into carbon dioxide and water. However, several nonoxidative mechanisms can also contribute to removal of organics. Sorption onto activated sludge can remove a large fraction of the colloidal and particulate wastewater organics. Intracellular storage of, e.g., polyhydroxyalkanoates (PHA), triacylglycerides (TAG), or wax esters can convert wastewater organics into precursors for high-value products. Recently, several environmental, economic, and technological drivers have stimulated research on nonoxidative removal of organics for wastewater treatment. In this paper, we review these nonoxidative removal mechanisms as well as the existing and emerging process configurations that make use of them for wastewater treatment. Better utilization of nonoxidative processes in activated sludge could reduce the wasteful aerobic oxidation of organic compounds and lead to more resource-efficient wastewater treatment plants.

Keywords: Adsorption; DLVO theory; colloids; contact-stabilization; high-rate activated sludge; polyhydroxyalkanoate; triacylglyceride.

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Figures

Figure 1.
Figure 1.
Schematic of a conventional activated sludge wastewater treatment plant.
Figure 2.
Figure 2.
Size fractionation of municipal (A) and industrial (B) wastewater. (1) This study was carried out by van Nieuwenhuijsen et al. (2004) in the Netherlands with a wastewater having a total COD concentration of 501 mg/L. (2) Dulekgurgen et al. (2006), Turkey, 406 mg/L. (3) Hu et al. (2002), USA, 300 mg/L. (4–6) Sophonsiri and Morgenroth (2004), USA, 309 mg/L, 67,444 mg/L, and 7249 mg/L, respectively. (7) Dogruel et al. (2006), Turkey, 1340 mg/L. (8) Karahan et al. (2008), Turkey, 3100 mg/L. (9) Arslan-Alaton et al. (2009), Turkey, 46,318 mg/L. (10) Dogruel et al. (2013), Turkey, 15,300 mg/L. For ultrafiltration membranes using nominal molecular weight cutoffs (MWCO), MWCO was converted to equivalent particle size assuming the following relationship: Diameter in nm = 2 × 0.066 × (MWCO in Da)0.333 (Erickson 2009).
Figure 3.
Figure 3.
Plot of nonsorbable organics concentration (a) and organic loading (F/M) from five studies. Note that data from Jorand et al. (1995) and Modin et al. (2015) was converted from TOC to COD assuming 2.7 gCOD/gTOC and that concentrations from those studies refer to organics smaller than 0.45 μm, concentrations from Guellil et al. (2001) and La Motta et al. (2004) refer to the nonsettleable fraction, and concentrations from Jimenez et al. (2005) refer to nonsettleable organics larger than 0.001 µm.
Figure 4.
Figure 4.
Schematic of a wastewater treatment plant with recirculation of waste activated sludge to the primary settlers.
Figure 5.
Figure 5.
Schematic of a contact-stabilization wastewater treatment plant.
Figure 6.
Figure 6.
Schematic of an adsorption–biooxidation (AB) process.
Figure 7.
Figure 7.
Schematic of an EBPR process.
Figure 8.
Figure 8.
Schematic of a PHA-producing wastewater treatment plant.
Figure 9.
Figure 9.
Schematic of wastewater treatment plant with lipid enhancement of waste sludge (adapted from Mondala et al. (2012) and Revellame et al. (2013)).
See this image and copyright information in PMC

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