Date of Completion

12-12-2016

Embargo Period

12-12-2016

Keywords

Cu, bioavailability, effluent, storm, organic matter, metal binding, algae, DGT, size fraction

Major Advisor

Timothy Vadas

Associate Advisor

Allison MacKay

Associate Advisor

John Clausen

Associate Advisor

Alexander Agrios

Associate Advisor

Ashley Helton

Field of Study

Environmental Engineering

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Urban streams receive Cu from both treated wastewater and stormwater runoff sources. Both sources have significant quantities of organic matter (OM), which is known to control Cu speciation and bioavailability. Individual and mixed water samples from wastewater treatment plant effluents, stormwater runoff, and streams from developed areas were characterized with respect to OM concentration and spectral properties and metal concentration and size distribution. In addition, asymmetric flow-field flow fractionation coupled to inductively coupled plasma mass spectrometry was used to measure concentration, size distribution and association of metals in the colloidal size range. Results reveal that Fe, Cu, Zn and Pb in the colloidal size range were mainly associated with the less than 5 nm, or less than 10 kDa size range. Cu was most strongly associated with OM, while Zn and Pb were mixed between Fe and OM. Effluent showed higher binding capacity for metals, while stormwater, even with higher OM concentrations showed more exchangeable metals. Upon mixing of source waters, colloidal metal concentrations and size distributions were conserved.

Dissolved OM was either left intact or separated into small (0-650 Da), medium (650 Da-50 kDa), or large (50 kDa-0.45 μm) size fractions using tangential flow filtration (TFF). Conditional stability constants of the OM were determined using competitive ligand exchange-solid phase extraction. Metal ligand concentrations were determined from Cu titrations. Conditional stability constants of the whole effluent OM were 0.5 to 1 log unit higher than those of stormwater OM for both hydrophilic and hydrophobic OM (Hydrophilic: Log KCu-eff-OMf = 8.2±0.2, Log KCu-storm-OM = 7.5±0.3; hydrophobic OM: Log KCu-eff-OM = 8.9±0.4, Log KCu-storm-OM = 7.9±0.1). The stability constants of the source

Hongwei Luan – University of Connecticut, 2016

OM were all higher than those of algae (Log KM-total = 6.3 and Log KM-intra = 6.8). Based on short-term uptake experiments, the results show there was 46% less total Cu uptake in the presence of effluent OM than stormwater OM, while intracellular Cu was about 25% less with effluent. This difference corresponded to the higher conditional stability constants measured for effluent OM than stormwater OM. We also found Cu mainly bound hydrophilic OM (80%) in effluent while it mainly bound hydrophobic OM (77%) in stormwater. Incorporating the conditional stability constants and metal ligand concentrations into an algal uptake model, the Cu uptake could be predicted. As for attachment to algal surfaces, stormwater OM promoted more accumulation of Cu on the algal surface, but this accounted for a small percentage of the total algal Cu content. Furthermore, there was a difference in Cu biouptake and stability constants between effluent and storm size fractions. For effluent OM, the Cu uptake and stability constants across size fractions were similar to the whole effluent. For stormwater OM the Cu stability constants were the lowest for the small size stormwater OM, resulting in more Cu uptake as stormwater OM size decreased. Differentiation between OM sources could lead to better predictions of metal uptake.

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