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Sorption and release of organics by primary, anaerobic, and aerobic activated sludge mixed with raw municipal wastewater.

Modin O, Saheb Alam S, Persson F, Wilén BM - PLoS ONE (2015)

Bottom Line: This study compared primary-, anaerobic-, and aerobic activated sludge as sorbents, determined sorption capacity and kinetics, and investigated some characteristics of the organics being sorbed.The 5-min sorption capacity of activated sludge was 6.5±10.8 mg total organic carbon (TOC) per g volatile suspend solids (VSS) for particulate organics and 5.0±4.7 mgTOC/gVSS for dissolved organics.The observed instantaneous sorption appeared to be mainly due to organics larger than 20 kDa in size being sorbed, although molecules with a size of about 200 Da with strong UV absorbance at 215-230 nm were also rapidly removed.

View Article: PubMed Central - PubMed

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

ABSTRACT
New activated sludge processes that utilize sorption as a major mechanism for organics removal are being developed to maximize energy recovery from wastewater organics, or as enhanced primary treatment technologies. To model and optimize sorption-based activated sludge processes, further knowledge about sorption of organics onto sludge is needed. This study compared primary-, anaerobic-, and aerobic activated sludge as sorbents, determined sorption capacity and kinetics, and investigated some characteristics of the organics being sorbed. Batch sorption assays were carried out without aeration at a mixing velocity of 200 rpm. Only aerobic activated sludge showed net sorption of organics. Sorption of dissolved organics occurred by a near-instantaneous sorption event followed by a slower process that obeyed 1st order kinetics. Sorption of particulates also followed 1st order kinetics but there was no instantaneous sorption event; instead there was a release of particles upon mixing. The 5-min sorption capacity of activated sludge was 6.5±10.8 mg total organic carbon (TOC) per g volatile suspend solids (VSS) for particulate organics and 5.0±4.7 mgTOC/gVSS for dissolved organics. The observed instantaneous sorption appeared to be mainly due to organics larger than 20 kDa in size being sorbed, although molecules with a size of about 200 Da with strong UV absorbance at 215-230 nm were also rapidly removed.

No MeSH data available.


Absorbance at 650 nm and 254 nm and concentrations of TOCp and TOCd in the mixtures of wastewater with effluent (Control), 0.30–0.33 gTSS/L of activated sludge (AS low), 1.04–1.16 gTSS/L of activated sludge (AS high), or activated that had been starved for either 1, 3 or 6 days.The low concentration of the starved sludge was 0.28–0.32 gTSS/L and the high concentration was 0.97–1.13 gTSS/L. The original TOC concentration and absorbance values before sedimentation are also shown. Averages of duplicate measurements are shown with the error bars representing the individual measurements. Arrow pairs indicate that the removal efficiencies for two treatments were compared. An asterisk (*) above the arrow pair indicate statistically significant difference in removal (p<0.05, n = 2).
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pone.0119371.g003: Absorbance at 650 nm and 254 nm and concentrations of TOCp and TOCd in the mixtures of wastewater with effluent (Control), 0.30–0.33 gTSS/L of activated sludge (AS low), 1.04–1.16 gTSS/L of activated sludge (AS high), or activated that had been starved for either 1, 3 or 6 days.The low concentration of the starved sludge was 0.28–0.32 gTSS/L and the high concentration was 0.97–1.13 gTSS/L. The original TOC concentration and absorbance values before sedimentation are also shown. Averages of duplicate measurements are shown with the error bars representing the individual measurements. Arrow pairs indicate that the removal efficiencies for two treatments were compared. An asterisk (*) above the arrow pair indicate statistically significant difference in removal (p<0.05, n = 2).

Mentions: Starvation of activated sludge may free up adsorption sites, which would allow greater removal of organic compounds from wastewater [24]. Therefore, activated sludge was starved for 1, 3, and 6 days and its sorption ability was compared to fresh sludge collected from the wastewater treatment plant (Fig. 3). After 1 day of starvation, the starved sludge performed approximately equal to the fresh sludge, both resulting in an improvement of the removal of particulate and dissolved substances compared to the control. Only for ABS650 and addition of low concentration of sludge did the starved sludge show significantly worse removal efficiency than the fresh activated sludge. After 3 days starvation, high addition of sludge resulted in significantly lower removal efficiency of ABS650, TOCp, and UV254. After 6 days starvation, addition of both low and high concentrations of starved sludge resulted in significantly worse removal efficiencies than fresh activated sludge for all parameters except TOCd. Under no circumstances did starved sludge perform better than fresh activated sludge. The reason may be that the fresh activated sludge was collected from the outlet of the aeration tanks at the wastewater treatment plant. Thus, organic substances taken up by the sludge in the treatment plant had already been metabolized and further starvation did not free up any additional adsorption sites. Instead, prolonged starvation (> 1 day) led to deflocculation of the sludge and release of particles (ABS650 and TOCp) and humic substances (UV254), which meant that addition of starved sludge to the wastewater had a negative effect on the removal efficiencies of these parameters.


Sorption and release of organics by primary, anaerobic, and aerobic activated sludge mixed with raw municipal wastewater.

Modin O, Saheb Alam S, Persson F, Wilén BM - PLoS ONE (2015)

Absorbance at 650 nm and 254 nm and concentrations of TOCp and TOCd in the mixtures of wastewater with effluent (Control), 0.30–0.33 gTSS/L of activated sludge (AS low), 1.04–1.16 gTSS/L of activated sludge (AS high), or activated that had been starved for either 1, 3 or 6 days.The low concentration of the starved sludge was 0.28–0.32 gTSS/L and the high concentration was 0.97–1.13 gTSS/L. The original TOC concentration and absorbance values before sedimentation are also shown. Averages of duplicate measurements are shown with the error bars representing the individual measurements. Arrow pairs indicate that the removal efficiencies for two treatments were compared. An asterisk (*) above the arrow pair indicate statistically significant difference in removal (p<0.05, n = 2).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4359093&req=5

pone.0119371.g003: Absorbance at 650 nm and 254 nm and concentrations of TOCp and TOCd in the mixtures of wastewater with effluent (Control), 0.30–0.33 gTSS/L of activated sludge (AS low), 1.04–1.16 gTSS/L of activated sludge (AS high), or activated that had been starved for either 1, 3 or 6 days.The low concentration of the starved sludge was 0.28–0.32 gTSS/L and the high concentration was 0.97–1.13 gTSS/L. The original TOC concentration and absorbance values before sedimentation are also shown. Averages of duplicate measurements are shown with the error bars representing the individual measurements. Arrow pairs indicate that the removal efficiencies for two treatments were compared. An asterisk (*) above the arrow pair indicate statistically significant difference in removal (p<0.05, n = 2).
Mentions: Starvation of activated sludge may free up adsorption sites, which would allow greater removal of organic compounds from wastewater [24]. Therefore, activated sludge was starved for 1, 3, and 6 days and its sorption ability was compared to fresh sludge collected from the wastewater treatment plant (Fig. 3). After 1 day of starvation, the starved sludge performed approximately equal to the fresh sludge, both resulting in an improvement of the removal of particulate and dissolved substances compared to the control. Only for ABS650 and addition of low concentration of sludge did the starved sludge show significantly worse removal efficiency than the fresh activated sludge. After 3 days starvation, high addition of sludge resulted in significantly lower removal efficiency of ABS650, TOCp, and UV254. After 6 days starvation, addition of both low and high concentrations of starved sludge resulted in significantly worse removal efficiencies than fresh activated sludge for all parameters except TOCd. Under no circumstances did starved sludge perform better than fresh activated sludge. The reason may be that the fresh activated sludge was collected from the outlet of the aeration tanks at the wastewater treatment plant. Thus, organic substances taken up by the sludge in the treatment plant had already been metabolized and further starvation did not free up any additional adsorption sites. Instead, prolonged starvation (> 1 day) led to deflocculation of the sludge and release of particles (ABS650 and TOCp) and humic substances (UV254), which meant that addition of starved sludge to the wastewater had a negative effect on the removal efficiencies of these parameters.

Bottom Line: This study compared primary-, anaerobic-, and aerobic activated sludge as sorbents, determined sorption capacity and kinetics, and investigated some characteristics of the organics being sorbed.The 5-min sorption capacity of activated sludge was 6.5±10.8 mg total organic carbon (TOC) per g volatile suspend solids (VSS) for particulate organics and 5.0±4.7 mgTOC/gVSS for dissolved organics.The observed instantaneous sorption appeared to be mainly due to organics larger than 20 kDa in size being sorbed, although molecules with a size of about 200 Da with strong UV absorbance at 215-230 nm were also rapidly removed.

View Article: PubMed Central - PubMed

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

ABSTRACT
New activated sludge processes that utilize sorption as a major mechanism for organics removal are being developed to maximize energy recovery from wastewater organics, or as enhanced primary treatment technologies. To model and optimize sorption-based activated sludge processes, further knowledge about sorption of organics onto sludge is needed. This study compared primary-, anaerobic-, and aerobic activated sludge as sorbents, determined sorption capacity and kinetics, and investigated some characteristics of the organics being sorbed. Batch sorption assays were carried out without aeration at a mixing velocity of 200 rpm. Only aerobic activated sludge showed net sorption of organics. Sorption of dissolved organics occurred by a near-instantaneous sorption event followed by a slower process that obeyed 1st order kinetics. Sorption of particulates also followed 1st order kinetics but there was no instantaneous sorption event; instead there was a release of particles upon mixing. The 5-min sorption capacity of activated sludge was 6.5±10.8 mg total organic carbon (TOC) per g volatile suspend solids (VSS) for particulate organics and 5.0±4.7 mgTOC/gVSS for dissolved organics. The observed instantaneous sorption appeared to be mainly due to organics larger than 20 kDa in size being sorbed, although molecules with a size of about 200 Da with strong UV absorbance at 215-230 nm were also rapidly removed.

No MeSH data available.