Bench scale studies were performed to evaluate removal and toxicity of copper nanoparticles (CuNPs) and copper ions in activated sludge biomass. The data indicated that, under the test conditions, copper nanoparticles were removed more effectively (∼95%) than copper ions (30-70%) from the wastewater. Mechanisms of CuNP removal were further investigated by equilibrating CuNP and copper ion in activated sludge filtrate (0.45 μm). The predominant mechanisms of copper removal appear to be aggregation and settling (CuNP) or precipitation (copper ion) rather than biosorption. Most probable number (MPN) test data indicated that addition of 10 mg/L of copper ion was toxic to both coliform and ammonia oxidizing bacteria in the wastewater while no inhibitory effects were observed with the addition of the same amount of copper nanoparticles. Respirometry data indicated a 55% decrease in respiration rate when 10 mg/L ionic copper was added. However, no significant decrease in respiration rate was observed in the presence of copper nanoparticles. The toxicity of copper to activated sludge microorganisms appears to be a function of the concentration and characteristics of copper remaining in solution/suspension.

The dynamic light scattering (DLS) technique can detect the concentration and size distribution of nanoscale particles in aqueous solutions by analyzing photon interactions. This study evaluated the applicability of using photon count rate data from DLS analyses for measuring levels of biogenic and manufactured nanoscale particles in wastewater. Statistical evaluations were performed using secondary wastewater effluent and a Malvern Zetasizer. Dynamic light scattering analyses were performed equally by two analysts over a period of two days using five dilutions and twelve replicates for each dilution. Linearity evaluation using the sixty sample analysis yielded a regression coefficient R(2) = 0.959. The accuracy analysis for various dilutions indicated a recovery of 100 ± 6%. Precision analyses indicated low variance coefficients for the impact of analysts, days, and within sample error. The variation by analysts was apparent only in the most diluted sample (intermediate precision ~12%), where the photon count rate was close to the instrument detection limit. The variation for different days was apparent in the two most concentrated samples, which indicated that wastewater samples must be analyzed for nanoscale particle measurement within the same day of collection. Upon addition of 10 mg l(-1) of nanosilica to wastewater effluent samples, the measured photon count rates were within 5% of the estimated values. The results indicated that photon count rate data can effectively complement various techniques currently available to detect nanoscale particles in wastewaters.

The production of zinc nanomaterial has increased significantly over the past several years and, as a result, nanoparticles have navigated their way into wastewater streams. The transportation and toxicity of zinc nanomaterial within the wastewater treatment processes is not well known. In this study, the zinc nanomaterial and its fate were characterized in an activated sludge treatment process. The tests performed included batch studies to evaluate abiotic and biotic removal, toxicity studies to evaluate inhibition to coliform and nitrifying bacteria, and bioreactor studies to evaluate impact on operating parameters. Stock solutions of zinc nanomaterial varied in size from 50 to 500 nm, but when added to an activated sludge solution, the nanoparticles agglomerated to larger sizes such that more than 60% of the zinc nanomaterial settled out of solution. However, when ionic zinc was added to activated sludge, more than 60% of the ionic zinc remained in suspension. It is likely that the ionic strength of the wastewater influenced the aggregation of the nanomaterial. Differences in the extent of removal between ionic and nano zinc species indicate that the mechanisms governing their removal are different. Toxicity analysis showed that zinc nanomaterial did not inhibit growth of coliform and ammonia oxidizing bacteria. However, ionic zinc inhibited the growth of both the coliform and ammonia oxidizing bacteria. Bioreactors were set up using activated sludge that was collected from a local treatment plant operating only in carbon oxidation mode. The treatment plant was operated at an SRT of 1.2 days and an MLSS of 650 mg/L. Several key parameters (COD, MLSS, pH) in the bioreactors were monitored through a 7-day incubation period, but showed no significant changes due to the addition of nano or ionic zinc. It is possible that the toxicity of zinc nanomaterial was not observed in these experiments because the nanomaterial agglomerated and settled out of solution.

Membrane processes are a widely used and a growing method to reclaim wastewater effluent.However, a major drawback is their energy intensity. Treating 1 million gallons of water requires in general 600-800 kW for microfiltration and 1,600-2,000 kW for reverse osmosis membranes.A better understanding of membrane fouling is key to reducing energy requirements, which in turn lower running costs. There are two fouling mechanisms: 1) the more known type is cake formation on the membrane caused by particles greater than 0.2 microns (backwashing and air sparging help mitigating this problem); 2) the lesser known is pore plugging caused by biogenic nanoparticles (< 0.2 microns), which is very difficult to mitigate. Nanoparticles have a higher potential to foul due to their smaller size. This phenomenon may account for up to 80% of flux reduction, causing irreversible fouling that necessitates costly chemical cleaning. Previously (Safarik and Phipps, 2006), studies at the Orange County Water District (OCWD) correlated fouling of microfiltration (MF) membranes with wastewater characteristics, using unfiltered, and pre-filtered wastewater (using 0.2 µm, 20K MWCO and 10K MWCO ultrafilters). This showed that removing nanoparticles larger than 200 nm only improved membrane performance by 20%. Nanoparticles larger than 3.5 nm (20KMWCO ultra filter) reduced membrane performance by 45%. But nanoparticles smaller than 2.5 nm (10K MWCO ultra filter) had little or no influence on membrane performance (Figure 1). In this study we wanted to further investigate the extent of nanoscale particles impact on membrane flux reduction and therefore on energy consumption.Samples were collected at the Santa Margarita Water District (SMWD), Irvine Ranch Water District (IRWD) and Orange County Sanitation District (OCSD) plants. At each plant samples were collected at several points (primary influent and effluent, secondary effluent) and a filtration series was conducted with 0.45, 0.2, 0.1, 0.08, 0.05, 0.03, and 0.01 micron membranes. At each step, filtrate was collected, COD was measured, and Zetasizer Nano analysis was performed to quantify particle size distribution and count rate (number of particles per second detected by the instrument, i.e. total amount of particles in the water). The photon count rate (expressed as kilocounts per second) is linearly correlated with the change in the filtration pore size (Figure 2). 518 Membrane Applications 2010