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Nonoxidative removal of organics in the activated sludge process.

Modin O, Persson F, Wilén BM, Hermansson M - Crit Rev Environ Sci Technol (2016)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Division of Water Environment Technology, Department of Civil and Environmental Engineering, Chalmers University of Technology , Gothenburg , Sweden.

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.

No MeSH data available.


Schematic of an EBPR process.
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f0007: Schematic of an EBPR process.

Mentions: The purpose of the EBPR process is to remove phosphorous from wastewater. Intermittent intracellular storage of organic compounds plays an important role for the biochemistry of the microorganisms involved. However, it should be noted that the organic compounds are not harvested from the wastewater as storage products, but are oxidized in the microbial cells during the aerobic or anoxic phase of the process. In the EBPR process, polyphosphate accumulating organisms (PAOs) are responsible for removing phosphorous from wastewater by storing it inside the cell as polyphosphate (Oehmen et al., 2007). Enrichment of PAOs can be achieved by cycling the activated sludge through anaerobic and aerobic conditions (Figure 7) (van Loosdrech et al., 1997; Seviour et al., 2003). Under anaerobic conditions, the activated sludge is mixed with wastewater containing VFAs. The PAOs take up the VFAs and store them as PHAs. The energy and reducing power required for PHA storage is obtained from intracellular reserves of polyphosphate and glycogen. Under aerobic conditions, the PAOs oxidize the stored pools of PHAs and instead store polyphosphate and glycogen (Mino et al., 1998). In EBPR systems, the PAOs can face unwanted competition from glycogen accumulating organisms (GAO), which take up VFAs under anaerobic conditions and store glycogen under aerobic conditions without storage of polyphosphate (Mino et al., 1995). The competition between PAOs and GAOs is, for example, affected by the VFA composition in the anaerobic phase where PAOs appear to have more rapid uptake of propionate. The propionate uptake rate was 0.18 ± 0.02 mol C/mol biomass C per hour irrespective of acetate concentration whereas the acetate uptake rate decreased from 0.21 ± 0.02 to 0.06 ± 0.01 mol C/mol biomass C per hour with increasing concentration of propionate in the VFA mixture (Carvalheira et al., 2014). Denitrifying glycogen accumulating organisms (DGAO) also compete for the available VFAs (Zeng et al., 2003).Figure 7.


Nonoxidative removal of organics in the activated sludge process.

Modin O, Persson F, Wilén BM, Hermansson M - Crit Rev Environ Sci Technol (2016)

Schematic of an EBPR process.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940897&req=5

f0007: Schematic of an EBPR process.
Mentions: The purpose of the EBPR process is to remove phosphorous from wastewater. Intermittent intracellular storage of organic compounds plays an important role for the biochemistry of the microorganisms involved. However, it should be noted that the organic compounds are not harvested from the wastewater as storage products, but are oxidized in the microbial cells during the aerobic or anoxic phase of the process. In the EBPR process, polyphosphate accumulating organisms (PAOs) are responsible for removing phosphorous from wastewater by storing it inside the cell as polyphosphate (Oehmen et al., 2007). Enrichment of PAOs can be achieved by cycling the activated sludge through anaerobic and aerobic conditions (Figure 7) (van Loosdrech et al., 1997; Seviour et al., 2003). Under anaerobic conditions, the activated sludge is mixed with wastewater containing VFAs. The PAOs take up the VFAs and store them as PHAs. The energy and reducing power required for PHA storage is obtained from intracellular reserves of polyphosphate and glycogen. Under aerobic conditions, the PAOs oxidize the stored pools of PHAs and instead store polyphosphate and glycogen (Mino et al., 1998). In EBPR systems, the PAOs can face unwanted competition from glycogen accumulating organisms (GAO), which take up VFAs under anaerobic conditions and store glycogen under aerobic conditions without storage of polyphosphate (Mino et al., 1995). The competition between PAOs and GAOs is, for example, affected by the VFA composition in the anaerobic phase where PAOs appear to have more rapid uptake of propionate. The propionate uptake rate was 0.18 ± 0.02 mol C/mol biomass C per hour irrespective of acetate concentration whereas the acetate uptake rate decreased from 0.21 ± 0.02 to 0.06 ± 0.01 mol C/mol biomass C per hour with increasing concentration of propionate in the VFA mixture (Carvalheira et al., 2014). Denitrifying glycogen accumulating organisms (DGAO) also compete for the available VFAs (Zeng et al., 2003).Figure 7.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Division of Water Environment Technology, Department of Civil and Environmental Engineering, Chalmers University of Technology , Gothenburg , Sweden.

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.

No MeSH data available.