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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.


HPSEC of samples from sorption tests with aerobic activated sludge and 1 min mixing.Black lines show controls without addition of sludge. Red lines show samples with addition of 0.97 g/L VSS. The vertical lines show the retention time of polyethylene glycol standards of known molecular weight.
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pone.0119371.g006: HPSEC of samples from sorption tests with aerobic activated sludge and 1 min mixing.Black lines show controls without addition of sludge. Red lines show samples with addition of 0.97 g/L VSS. The vertical lines show the retention time of polyethylene glycol standards of known molecular weight.

Mentions: The fate of small molecules (<20 kDa) in the sorption tests was investigated using HPSEC. In this size range, most of the organic molecules were smaller than 2 kDa (Fig. 6). Detection at wavelengths of 215, 230, 254, and 280 nm was carried out. However, the results at 215 and 230 nm were very similar to each other, and so were the results at 254 and 280 nm. Therefore, only the results at 215 and 254 nm are shown in Fig. 6. Organic compounds with functional groups such as carboxyls, carboxylates, aldehydes, ketones, and esters have absorption maxima near 200 nm [25], and these groups are likely detected in the HPSEC spectra at 215 nm. At longer wavelengths, aromatic organic compounds have absorption peaks. Benzene and more complex aromatic molecules such as humic acids have absorption peaks near 254 nm and this wavelength is often used as an indicator of natural organic matter in water [26]. Proteins usually have absorption peaks near 280 nm because of the aromatic amino acids tryptophan and tyrosine [27]. Fig. 6 shows samples after 1 min of mixing, thus the effect of the near-instantaneous sorption event can be observed. At 215 nm, there is a clear difference between sorption tests and controls for molecules of 200 Da and less. This suggests that small molecules such as carboxylic acids may have been rapidly taken up by the sludge upon mixing. At 254 nm, there is no obvious difference between control and sorption test samples for molecules smaller than 20 kDa. As the TOCd values in the kinetic tests were obtained by correlation with ABS254 values, this suggests that the instantaneous sorption of TOCd observed in Fig. 4 is due to dissolved organic matter larger than 20 kDa. The HPSEC spectra obtained after mixing 15 and 120 min are shown in S3 File. For the short wavelengths (215 and 230 nm) the sorption tests samples are still distinctly different from the control around 200 Da at 15 min. However, at 120 min the absorbance at this size range has increased drastically both for the control and test samples, possibly because of fermentation leading to the production of carboxylic acids. At the longer wavelengths (254 and 280 nm), the absorbance of molecules smaller than 200 Da decreases with time in the sorption test samples whereas the control samples remain fairly constant. At 120 min, there is a clear difference between the controls and the test samples. This suggests that prolonged mixing with sludge leads to uptake or conversion of the aromatic fraction of organic molecules smaller than 200 Da.


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)

HPSEC of samples from sorption tests with aerobic activated sludge and 1 min mixing.Black lines show controls without addition of sludge. Red lines show samples with addition of 0.97 g/L VSS. The vertical lines show the retention time of polyethylene glycol standards of known molecular weight.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4359093&req=5

pone.0119371.g006: HPSEC of samples from sorption tests with aerobic activated sludge and 1 min mixing.Black lines show controls without addition of sludge. Red lines show samples with addition of 0.97 g/L VSS. The vertical lines show the retention time of polyethylene glycol standards of known molecular weight.
Mentions: The fate of small molecules (<20 kDa) in the sorption tests was investigated using HPSEC. In this size range, most of the organic molecules were smaller than 2 kDa (Fig. 6). Detection at wavelengths of 215, 230, 254, and 280 nm was carried out. However, the results at 215 and 230 nm were very similar to each other, and so were the results at 254 and 280 nm. Therefore, only the results at 215 and 254 nm are shown in Fig. 6. Organic compounds with functional groups such as carboxyls, carboxylates, aldehydes, ketones, and esters have absorption maxima near 200 nm [25], and these groups are likely detected in the HPSEC spectra at 215 nm. At longer wavelengths, aromatic organic compounds have absorption peaks. Benzene and more complex aromatic molecules such as humic acids have absorption peaks near 254 nm and this wavelength is often used as an indicator of natural organic matter in water [26]. Proteins usually have absorption peaks near 280 nm because of the aromatic amino acids tryptophan and tyrosine [27]. Fig. 6 shows samples after 1 min of mixing, thus the effect of the near-instantaneous sorption event can be observed. At 215 nm, there is a clear difference between sorption tests and controls for molecules of 200 Da and less. This suggests that small molecules such as carboxylic acids may have been rapidly taken up by the sludge upon mixing. At 254 nm, there is no obvious difference between control and sorption test samples for molecules smaller than 20 kDa. As the TOCd values in the kinetic tests were obtained by correlation with ABS254 values, this suggests that the instantaneous sorption of TOCd observed in Fig. 4 is due to dissolved organic matter larger than 20 kDa. The HPSEC spectra obtained after mixing 15 and 120 min are shown in S3 File. For the short wavelengths (215 and 230 nm) the sorption tests samples are still distinctly different from the control around 200 Da at 15 min. However, at 120 min the absorbance at this size range has increased drastically both for the control and test samples, possibly because of fermentation leading to the production of carboxylic acids. At the longer wavelengths (254 and 280 nm), the absorbance of molecules smaller than 200 Da decreases with time in the sorption test samples whereas the control samples remain fairly constant. At 120 min, there is a clear difference between the controls and the test samples. This suggests that prolonged mixing with sludge leads to uptake or conversion of the aromatic fraction of organic molecules smaller than 200 Da.

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.