2012 Progress Report: Uptake of Specific Engineered Nanoparticles (ENP) by Sludge Particulates as Affected by the Presence of Dissolved Organic Matters (DOM)EPA Grant Number: R834859
Title: Uptake of Specific Engineered Nanoparticles (ENP) by Sludge Particulates as Affected by the Presence of Dissolved Organic Matters (DOM)
Investigators: Huang, C. P. , Johnston, Murray V.
Institution: University of Delaware
EPA Project Officer: Lasat, Mitch
Project Period: February 1, 2011 through January 31, 2014
Project Period Covered by this Report: February 1, 2012 through January 31,2013
Project Amount: $599,678
RFA: Increasing Scientific Data on the Fate, Transport and Behavior of Engineered Nanomaterials in Selected Environmental and Biological Matrices (2010) RFA Text | Recipients Lists
Research Category: Nanotechnology , Safer Chemicals
The major objective of this research is to accurately evaluate the amount of ENP that flow through the wastewater treatment plant (WWTP). A mass balance of the ENP in the wastewater treatment plant was calculated to (1) measure the total amount of particles that flow through the WWTP, (2) understand the distribution of ENP within the WWTP, and (3) speculate their interaction with wastewater sludge. In short, the mass balance was calculated to better understand the characteristics and impacts of ENP in a given WWTP.
An additional goal was to study the uptake and interaction of ENP by wastewater and its constituents. The extent of ENP uptake by sludge and its constituents was studied by determining the amount of ENP sorbed as a function of free ENP concentration (sorption isotherms) using differential sedimentation methods.
We have successfully modified methods for ENP quantification in municipal WWTP. Pretreatment methods were modified using acid digestion to prevent particle loss. Dialysis and the wet peroxide method was used for oxidation followed by acid digestion. With the dialysis used to remove the dissolved metals, the acid digestion was used to dissolve the remaining metallic particles for maximum particle detection. Filtration was conducted on the digested samples to verify the degree of digestion. Results of the modified method showed higher concentrations of metallic ENP compared with the conventional method indicating optimal particle measurement.
Based on the modified method concentration profiles of inherent ENP was measured throughout the WWTP. A mass flux of ENP was calculated with the measured concentration and hydraulic flow data. Compared with the concentration data, the mass flux was more accurate in estimating the particle distribution within the WWTP due to the consideration of sludge recirculation. Results showed an 80% loss of Ti and 75% loss of Zn by waste or return sludge. The error of the mass balance showed to be 7.5% for Zn and minimal for Ti both lower than the standard deviation of the results.
Sediment experiments were conducted to measure the adsorption of ENP onto sludge. The sludge was separated into four different fractions. Experiments were conducted with TiO2 and Zn for ENP and primary and secondary sludge. Due to the surface charge, ZnO exhibited stronger affinity to dissolved organic matters (DOM) than TiO2. The second series of sediment experiments were conducted with small organic particles (<1µm) and DOM where the sample was named supernatant. Compared with the samples containing only DOM, the supernatant showed a significant amount of sedimentation with both ZnO and TiO2. Sedimentation experiments with large organic particles show a sharper decrease in the turbidity followed by a steady curve indicating that most of the NP in the sample is adsorbed to the large organic particles via differential sedimentation.
Ongoing research efforts will be focused on the fate and impact of ENP to sludge and other constituents. For insight to the fate, interaction of ENP with sludge particulates and other constituents of sludge will be tested for adsorption experiments. Sludge will be separated based on the size of the organic particles. Sedimentation experiments will be coupled with additional experiments to evaluate the adsorption characteristics of ENP to sludge.
For the impact of ENP, toxicity experiments will be conducted to evaluate the inhibition effect of particles on microbes in the sludge. Batch reactors will be operated in the laboratory as model wastewater treatment plants. Different concentrations of ENP will be injected into separate reactors for a toxicity profile. Additional experiments will also be conducted for the overall impact of ENP. Oxidation uptake rates (OUR) will be measured for the respiratory inhibition as well as the EC50 for the critical concentrations. Batch experiments to obtain the Michaelis-Menten equation for the inhibition factor will be conducted as well.
We will continue to develop and refine ways to aerosolize nanoparticles from aqueous solutions and to chemically characterize them. We will also begin to explore reactivity by exposing the particles to oxidants in a flow tube reactor.