Jinwoo Cho

Inhibition of total oxygen uptake by silica nanoparticles in activated sludge

Nanoparticle toxicity to biological activities in activated sludge is largely unknown. Among the widely used nanoparticles, silica nanoparticles (SNP) have a limited number of studies associated with inhibition to the activated sludge process (ASP). We demonstrated SNP inhibition of activated sludge respiration through oxygen uptake rate (OUR) measurement. Based on the percentage inhibition of total oxygen consumption (IT), we observed that smaller SNPs (12 nm, IT=33 ± 3%; 151 nm, IT=23 ± 2%) were stronger inhibitors than larger SNPs (442 and 683 nm, IT=5 ± 1%). Transmission electron micrographs showed that some of the SNPs were adsorbed on and/or apparently embedded somewhere in the microbial cell membrane. Whether SNPs are directly associated with the inhibition of total oxygen uptake warrants further studies. However, it is clear that SNPs statistically significantly altered the composition of microbial membrane lipids, which was more clearly described by principal component analysis and weighted Euclidian distance (PCA-ED) of the fatty acid methyl ester (FAME) data. This study suggests that SNPs potentially affect the biological activity in activated sludge through the inhibition of total oxygen uptake.

Obtaining Real-Time Kinetic Parameters on Ozone Decay from a Full-Scale Ozone Contactor Using the Axial Dispersion Reactor Model

Ozone decay kinetic parameters, including fast ozone demand ([D]0), ozone decay rate constant (kD), and rate constant for ozone reaction with ozone demand (kR), are required for a numerical simulation targeting the design and operational optimization of an ozone contactor. The kinetic parameters of ozone decay and dispersion number were obtained from a full-scale ozone contactor for the axial dispersion reactor model simulation. The sensitivity analysis showed that the influence of kR was minor and the constant 13 L mg−1 min−1 for kR was suitable for carrying out simulations for sand-filtered raw water without measuring it. Curve fitting with on-site ozone concentrations and the ADR simulation results using a trial-and-error method could successfully provide kinetic parameters on ozone decay (i.e., kD and [D]0). Using these real-time kinetic parameters, we successfully predicted the CT, residual ozone, C. parvum log inactivation, and bromate formation. Compared to a method based on the CSTR in series, this method could provide more accurate CT and residual ozone for an ozone contactor with horizontal meandering flow and low dispersion number.

Fluorescent nano particle application for a membrane surface integrity test: Sensitivity, stability, and reliability of the particles

Abstract In this research, silica-based fluorescent particles were synthesized and used as a surrogate detector to evaluate the integrity of a compromised flat sheet membrane. Three different sizes of particles were synthesized and dyed with a fluorescent dye to make a fluorescence image under a UV light. Experiments were designed to test the sensitivity of the detection limit, stability of particles, and reliability of the proposed method. UV spectrometer and image analysis were used to evaluate the detection limits and measure the concentration and mass of the particles in the feed and permeate. For the stability of the particles, dye-leakage tests were conducted to estimate the amount of fluorescent decay when fluorescent particles were dissolved in an aqueous solvent. The effect of the particles on the membrane fouling was also investigated by conducting a batch filtration test of undamaged membranes. To examine the reliability of the proposed method, a series of filtration tests were performed with t...