Pagán-Incle, Keila M.

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    Impact assessment of the presence of engineered iron oxide nanoparticles on wastewater effluent disinfection
    (2014) Pagán-Incle, Keila M.; Hwang, Sangchul; College of Engineering; Bogere, Moses N.; Tarafa-Vélez, Pedro; Department of Civil Engineering; Arroyo, José
    A previous study indicated that ~8.7% wt. Fe of the initially dosed engineered iron oxide nanoparticles coated with surfactants (ENPFe-Surf), as contaminants, was present in the effluent from the lab-scale sequencing batch reactors (SBRs). It was suggested that presence of ENPFe-Surf might impact disinfection of wastewater effluents. Therefore, this study assessed the interactions among chlorine, ENPFe-Surf and fecal coliforms (FC) in batch and plug flow reactor (PFR) disinfection processes using real wastewater effluent collected from a local wastewater treatment plant. Then, the characteristics of the settled SBR sludge incorporating ENPFe-Surf were examined in order to validate the previous study aforementioned. The results from batch disinfection studies showed that ENPFe-Surf produced adverse (unfavorable) effects on FC disinfection. To achieve a 4-log FC removal, the required free chlorine residuals were 0.22, 0.18, and 0.10 mg Cl2 L-1 for contact times of 24, 30, and 60 minutes in the absence of ENPFe-Surf. In comparison, when ENPFe-Surf was present at 4.97 mg L-1 as Fe, the required free chlorine residual concentrations were 0.18, 0.14, and 0.07 mg Cl2 L-1 for the same contact times, respectively, to achieve the same log removal of FC. More log FC removal was achieved for the same chlorine consumption in the absence of ENPFe-Surf compared to values when it is present due to additional chlorine consumption (i.e., scavenging) with ENPFe- Surf. The results from PFR disinfection studies showed scavenging effects of ENPFe-Surf on chlorine as well: ~5% of the added chlorine concentration was still measured at pseudo steady state in the presence of ENPFe-Surf, while ~10% was observed in the absence of ENPFe-Surf. In general, FC log removals were proportional to CT values (the product of the residual disinfectant concentration, C, in mg L-1 times the contact time, T, in min), whether or not ENPFe-Surf was present. The same FC log removal at the same disinfection contact time was accomplished in PFR at lower concentrations of free chlorine residuals in the presence of ENPFe-Surf compared to its absence. Again, this was due to scavenging effect of ENPFe-Surf on chlorine, which reduces chlorine residuals available for FC disinfection and, thereby, poorer FC disinfection efficiency. The settled activated sludge of the SBR run in the presence of ENPFe-Surf had different characteristics from that of the control SBR run without ENPFe-Surf present. It had unique iron- rich, hexagon-shaped compounds. This implies that the presence of ENPFe-Surf modifies the physicochemical properties of the sludge and could alter the efficiency in the sludge management.