Martínez-Pérez, Diana E.

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    Effect of engineering iron oxide nanoparticles on effluent water quality from biological wastewater treatment
    (2013) Martínez-Pérez, Diana E.; Hwang, Sangchul; College of Engineering; Benitez, Jaime; Zapata López, Raúl E.; Department of Civil Engineering; Harmsen, Eric
    The production, use, and disposal of products containing nanoparticles may lead to their appearance in air, water, and soil, and subsequently in the human body. Because there is no existing regulation, large amounts of used or wasted engineered nanoparticles may be discharged into sewer systems and eventually enter wastewater treatment plants. Wastewater treatment plants can play an important role in controlling engineered nanoparticles release from the sources to the aquatic environmental receptors via treated effluent discharge, or to the terrestrial environments via sludge disposal to land. Effluent wastewater quality from a lab-scale sequencing batch reactor (SBR) was evaluated with the different loadings of engineered iron oxide nanoparticles coated with a surfactant (ENPFe-surf). Lab-scale SBRs were run at different hydraulic retention times (HRT, 3 and 6 hrs), a 0.5-hr sedimentation, and a 0.5-hr decant/refill at a food-to-microorganisms ratio of 0.32 g BOD/g MLSS/day. The SBRs were stabilized by running up to the 6th cycle under the same experimental conditions. At the onset of the 7th-10th cycles, the treatment SBRs were loaded with ENPFe-surf at either 29.6 or 88.9 mg as soluble Fe per L of mixed liquors. Physiochemical influence of ENP on water quality parameters was tested, including pH, turbidity, and chemical oxygen demand, biological oxygen demand, and Fe concentrations. Results showed that about ~8.7% of ENPFe-surf applied were present in the effluent stream of the treatment SBR regardless of ENPFe-surf loadings. The stable presence of ENPFe-surf was confirmed with the analyses of mean particle diameters and Fe concentrations in the effluent. Consequently, results showed that statistically significant (p<0.05) increases were found for turbidity, apparent color and soluble chemical oxygen demand in the treatment SBR effluents, compared to those in the effluents of the control SBRs that were run in parallel without ENPFe-surf loadings. Biological oxygen demand concentrations were insignificantly higher in the effluents of the treatment SBRs than in those of the control SBRs. In general, these findings implied that ENPFe-surf would be introduced into environmental receptors through the treated effluent and could potentially impact them. Effluent suspended solid concentrations were not significantly different between the control and treatment SBRs. ENPFe-surf loadings to the mixed liquors produced inhibitory respiration resulting in decreased oxygen uptake rate. Twice longer aeration time did not produce significant differences in any of water quality parameters. Such insignificant differences in water quality deterioration was attributed to the presence of the similar ENPFe-surf concentrations in the effluent at 2.3±0.3 and 2.7±0.5 mg/L as Fe for the treatment SBRs run at hydraulic retention time of 3- and 6- hrs, respectively. Low ENPFe-surf concentrations (<10 mg/L as soluble Fe) in the SBR effluent were unlikely to produce significantly adversary effect on the removal and inactivation of fecal coliforms in disinfection process. Although greater (p>0.05) chlorine demand was found proportionally to the ENPFe-surf loadings, disinfection of fecal coliforms at the ENPFe-surf concentrations lower than 3 mg/L as Fe was not affected, achieving 100% fecal coliform removals at the initial chlorine concentration of either 5.7 or 11.4 mg/L.