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Meta-analysis of mass balances examining chemical fate during wastewater treatment.

Heidler J, Halden RU - Environ. Sci. Technol. (2008)

Bottom Line: Occurrence data for organic wastewater compounds detected in digested sludge followed a simple nonlinear model that required only K(OW) or K(OC) as the input and yielded a correlation coefficient of 0.9 in both instances.The model predicted persistence in biosolids for the majority (> 50%) of the input load of organic wastewater compounds featuring a log10 K(OW) value of greater than 5.2 (log10 K(OC) > 4.4).In contrast, hydrophobicity had no or only limited value for estimating, respectively, phi and the overall persistence of a chemical during conventional wastewater treatment.

View Article: PubMed Central - PubMed

Affiliation: Johns Hopkins University Center for Water and Health, Department of Environmental Health Sciences, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland 21205, USA.

ABSTRACT
Mass balances are an instructive means for investigating the fate of chemicals during wastewater treatment. In addition to the aqueous-phase removal efficiency (phi), they can inform on chemical partitioning, transformation, and persistence, as well as on the chemical loading to streams and soils receiving, respectively, treated effluent and digested sewage sludge (biosolids). Release rates computed on a per-capita basis can serve to extrapolate findings to a larger scale. This review examines over a dozen mass balances conducted for various organic wastewater contaminants, including prescription drugs, estrogens, fragrances, antimicrobials, and surfactants of differing sorption potential (hydrophobicity), here expressed as the 1-octanol-water partition coefficient (K(OW)) and the organic carbon normalized sorption coefficient (K(OC)). Major challengesto mass balances are the collection of representative samples and accurate quantification of chemicals in sludge. A meta-analysis of peer-reviewed data identified sorption potential as the principal determinant governing chemical persistence in biosolids. Occurrence data for organic wastewater compounds detected in digested sludge followed a simple nonlinear model that required only K(OW) or K(OC) as the input and yielded a correlation coefficient of 0.9 in both instances. The model predicted persistence in biosolids for the majority (> 50%) of the input load of organic wastewater compounds featuring a log10 K(OW) value of greater than 5.2 (log10 K(OC) > 4.4). In contrast, hydrophobicity had no or only limited value for estimating, respectively, phi and the overall persistence of a chemical during conventional wastewater treatment.

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Schematic illustrating the role of sorption in the fate of organic wastewater compounds during their hypothetical passage through a conventional activated sludge wastewater treatment plant assuming a lack of both transformation and loss processes. The partitioning of compounds between the dissolved phase (blue) and wastewater solids (orange) is shown for three organic wastewater compounds featuring logarithmic organic carbon normalized sorption coefficients (log KOC) of 2, 4, and 6 (top, middle, and bottom panels, respectively).
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fig2: Schematic illustrating the role of sorption in the fate of organic wastewater compounds during their hypothetical passage through a conventional activated sludge wastewater treatment plant assuming a lack of both transformation and loss processes. The partitioning of compounds between the dissolved phase (blue) and wastewater solids (orange) is shown for three organic wastewater compounds featuring logarithmic organic carbon normalized sorption coefficients (log KOC) of 2, 4, and 6 (top, middle, and bottom panels, respectively).

Mentions: The schematic in Figure 2 illustrates the influence of sorption due to hydrophobic interactions for three different types of compounds featuring low, intermediate, and high log KOC values of 2, 4, and 6, respectively. A very hydrophobic organic compound (vHOC; here defined as having a log KOC of ≥6) entering the plant at a concentration of 10 μg/L is reduced in mass by at least one-third of its initial loading, because of sorption to primary sludge in the primary clarifiers (Figure 2). Thus, a considerable fraction (≥35%) of the vHOC loading to the plant never reaches the aerobic treatment step of activated sludge processing and instead is subjected to (typically anaerobic) sludge digestion only (12,13). For the remaining vHOC mass passing through the clarifier in primary effluent, this process of sequestration into particulates and removal with sludge is repeated during secondary treatment, which typically consists of aerobic degradation followed by sedimentation in secondary clarifiers. In contrast to primary treatment, effective residence times of vHOCs in the aerobic sludge process exceed those of hydrophilic compounds, because of the extensive recycling of solids (Figure 2). Removal of particulates during secondary clarification further depletes the vHOC mass, because of preferential partitioning of the compounds into activated sludge (typical solids content of 0.8−1.2%) (22). This sequential partitioning process effectively renders vHOC concentrations in final effluent at very low levels; even in the absence of any biological, chemical, or physical transformation, the aqueous-phase removal efficiency will be at least 97%. In contrast, the aqueous-phase removal efficiency for moderately hydrophobic (e.g., triclosan, estrogens) (9,14) and more hydrophilic OWCs (e.g., sulfamethoxazole, trimethoprim, and carbamazepine) (17,23) featuring log KOC values of 4 and 2 is on the order of 87 and 17%, respectively, if sorption represents the only removal mechanism (Figure 2).


Meta-analysis of mass balances examining chemical fate during wastewater treatment.

Heidler J, Halden RU - Environ. Sci. Technol. (2008)

Schematic illustrating the role of sorption in the fate of organic wastewater compounds during their hypothetical passage through a conventional activated sludge wastewater treatment plant assuming a lack of both transformation and loss processes. The partitioning of compounds between the dissolved phase (blue) and wastewater solids (orange) is shown for three organic wastewater compounds featuring logarithmic organic carbon normalized sorption coefficients (log KOC) of 2, 4, and 6 (top, middle, and bottom panels, respectively).
© Copyright Policy - open-access - ccc-price
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2665886&req=5

fig2: Schematic illustrating the role of sorption in the fate of organic wastewater compounds during their hypothetical passage through a conventional activated sludge wastewater treatment plant assuming a lack of both transformation and loss processes. The partitioning of compounds between the dissolved phase (blue) and wastewater solids (orange) is shown for three organic wastewater compounds featuring logarithmic organic carbon normalized sorption coefficients (log KOC) of 2, 4, and 6 (top, middle, and bottom panels, respectively).
Mentions: The schematic in Figure 2 illustrates the influence of sorption due to hydrophobic interactions for three different types of compounds featuring low, intermediate, and high log KOC values of 2, 4, and 6, respectively. A very hydrophobic organic compound (vHOC; here defined as having a log KOC of ≥6) entering the plant at a concentration of 10 μg/L is reduced in mass by at least one-third of its initial loading, because of sorption to primary sludge in the primary clarifiers (Figure 2). Thus, a considerable fraction (≥35%) of the vHOC loading to the plant never reaches the aerobic treatment step of activated sludge processing and instead is subjected to (typically anaerobic) sludge digestion only (12,13). For the remaining vHOC mass passing through the clarifier in primary effluent, this process of sequestration into particulates and removal with sludge is repeated during secondary treatment, which typically consists of aerobic degradation followed by sedimentation in secondary clarifiers. In contrast to primary treatment, effective residence times of vHOCs in the aerobic sludge process exceed those of hydrophilic compounds, because of the extensive recycling of solids (Figure 2). Removal of particulates during secondary clarification further depletes the vHOC mass, because of preferential partitioning of the compounds into activated sludge (typical solids content of 0.8−1.2%) (22). This sequential partitioning process effectively renders vHOC concentrations in final effluent at very low levels; even in the absence of any biological, chemical, or physical transformation, the aqueous-phase removal efficiency will be at least 97%. In contrast, the aqueous-phase removal efficiency for moderately hydrophobic (e.g., triclosan, estrogens) (9,14) and more hydrophilic OWCs (e.g., sulfamethoxazole, trimethoprim, and carbamazepine) (17,23) featuring log KOC values of 4 and 2 is on the order of 87 and 17%, respectively, if sorption represents the only removal mechanism (Figure 2).

Bottom Line: Occurrence data for organic wastewater compounds detected in digested sludge followed a simple nonlinear model that required only K(OW) or K(OC) as the input and yielded a correlation coefficient of 0.9 in both instances.The model predicted persistence in biosolids for the majority (> 50%) of the input load of organic wastewater compounds featuring a log10 K(OW) value of greater than 5.2 (log10 K(OC) > 4.4).In contrast, hydrophobicity had no or only limited value for estimating, respectively, phi and the overall persistence of a chemical during conventional wastewater treatment.

View Article: PubMed Central - PubMed

Affiliation: Johns Hopkins University Center for Water and Health, Department of Environmental Health Sciences, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland 21205, USA.

ABSTRACT
Mass balances are an instructive means for investigating the fate of chemicals during wastewater treatment. In addition to the aqueous-phase removal efficiency (phi), they can inform on chemical partitioning, transformation, and persistence, as well as on the chemical loading to streams and soils receiving, respectively, treated effluent and digested sewage sludge (biosolids). Release rates computed on a per-capita basis can serve to extrapolate findings to a larger scale. This review examines over a dozen mass balances conducted for various organic wastewater contaminants, including prescription drugs, estrogens, fragrances, antimicrobials, and surfactants of differing sorption potential (hydrophobicity), here expressed as the 1-octanol-water partition coefficient (K(OW)) and the organic carbon normalized sorption coefficient (K(OC)). Major challengesto mass balances are the collection of representative samples and accurate quantification of chemicals in sludge. A meta-analysis of peer-reviewed data identified sorption potential as the principal determinant governing chemical persistence in biosolids. Occurrence data for organic wastewater compounds detected in digested sludge followed a simple nonlinear model that required only K(OW) or K(OC) as the input and yielded a correlation coefficient of 0.9 in both instances. The model predicted persistence in biosolids for the majority (> 50%) of the input load of organic wastewater compounds featuring a log10 K(OW) value of greater than 5.2 (log10 K(OC) > 4.4). In contrast, hydrophobicity had no or only limited value for estimating, respectively, phi and the overall persistence of a chemical during conventional wastewater treatment.

Show MeSH
Related in: MedlinePlus