Markus Boller

Synthetic TiO2 nanoparticle emission from exterior facades into the aquatic environment

We present direct evidence of the release of synthetic nanoparticles from urban applications into the aquatic environment. We investigated TiO(2) particles as these particles are used in large quantities in exterior paints as whitening pigments and are to some extent also present in the nano-size range. TiO(2) particles were traced from exterior facade paints to the discharge into surface waters. We used a centrifugation based sample preparation which recovers TiO(2) particles between roughly 20 and 300nm. Analytical electron microscopy revealed that TiO(2) particles are detached from new and aged facade paints by natural weather conditions and are then transported by facade runoff and are discharged into natural, receiving waters. Microscopic investigations are confirmed by bulk chemical analysis. By combining results from microscopic investigations with bulk chemical analysis we calculated the number densities of synthetic TiO(2) particles in the runoff.

Release of silver nanoparticles from outdoor facades

In this study we investigate the release of metallic silver nanoparticles (Ag-NP) from paints used for outdoor applications. A facade panel mounted on a model house was exposed to ambient weather conditions over a period of one year. The runoff volume of individual rain events was determined and the silver and titanium concentrations of 36 out of 65 runoff events were measured. Selected samples were prepared for electron microscopic analysis. A strong leaching of the Ag-NP was observed during the initial runoff events with a maximum concentration of 145 micro Ag/l. After a period of one year, more than 30% of the Ag-NP were released to the environment. Particles were mostly <15 nm and are released as composite colloids attached to the organic binders of the paint. Microscopic results indicate that the Ag-NP are likely transformed to considerably less toxic forms such as Ag2S.

Influence of interactions between NOM and particles on UF fouling mechanisms

This study focused on the mechanistic effects of molecular interactions between inorganic particles (kaolinite) and the two main NOM fouling fractions of polysaccharides (alginate) and humics (humic acids) in ultrafiltration. Fouling effects were studied during the dead-end filtration of individual and mixed compounds as well as during the subsequent filtration of individual compounds. SEM analyses were performed to further study the fouling-layer structure. A significant synergistic effect was observed during combined particle-NOM fouling, which was considerably greater than the sum of particle and organic fouling alone. Synergistic fouling could be explained by NOM-particle interactions in the feed solution and during the fouling process. Kaolinite alone formed a fouling layer of particle aggregates, whereas humic acid adsorption onto kaolinite resulted in a fouling layer of stabilized colloids of humic acid and kaolinite. In the case of alginate, simultaneous pore-blocking and cake-layer formation of NOM and kaolinite dominated the fouling. In both cases, incorporation of the organics in the kaolinite fouling layer resulted in a fouling cake of significantly reduced porosity compared to individual particle filtration. Irreversible fouling by NOM could not be prevented by kaolinite. SEM images showed patches of the particle-fouling layer remaining on the membrane surface after backwashing, which can be linked to particle-membrane associations by NOM bridging.

Characterization of natural organic matter adsorption in granular activated carbon adsorbers

The removal of natural organic matter (NOM) from lake water was studied in two pilot-scale adsorbers containing granular activated carbon (GAC) with different physical properties. To study the adsorption behavior of individual NOM fractions as a function of time and adsorber depth, NOM was fractionated by size exclusion chromatography (SEC) into biopolymers, humics, building blocks, and low molecular weight (LMW) organics, and NOM fractions were quantified by both ultraviolet and organic carbon detectors. High molecular weight biopolymers were not retained in the two adsorbers. In contrast, humic substances, building blocks and LMW organics were initially well and irreversibly removed, and their effluent concentrations increased gradually in the outlet of the adsorbers until a pseudo-steady state concentration was reached. Poor removal of biopolymers was likely a result of their comparatively large size that prevented access to the internal pore structure of the GACs. In both GAC adsorbers, adsorbability of the remaining NOM fractions, compared on the basis of partition coefficients, increased with decreasing molecular size, suggesting that increasingly larger portions of the internal GAC surface area could be accessed as the size of NOM decreased. Overall DOC uptake at pseudo-steady state differed between the two tested GACs (18.9 and 28.6 g-C/kg GAC), and the percent difference in DOC uptake closely matched the percent difference in the volume of pores with widths in the 1-50 nm range that was measured for the two fresh GACs. Despite the differences in NOM uptake capacity, individual NOM fractions were removed in similar proportions by the two GACs.

Pollution of soil and groundwater from infiltration of highly contaminated stormwater - a case study

A surface and a sub-surface infiltration system that received runoff water from trafficked roads for several decades was dug up and the contamination with heavy metals, PAH and AOX was investigated. Most measured solid phase concentrations exceeded background concentrations in nearby surface soils and sub-surface sediments and some even exceeded guidelines fixed to preserve the fertility of soil. However, the contamination decreased rapidly with depth. None of the measured metal concentrations in simulated soil solutions exceeded defined drinking water quality standards. Surprisingly, the surface and the sub-surface infiltration system seemed to be equally good at retaining pollution. This indicates that the runoff sludge found in such infiltration systems plays an important role both as a source and a sorbent for stormwater contaminants. The study does not point at a considerable risk for groundwater contamination due to stormwater infiltration, but highlights that well absorbable contaminants readily available in urban stormwater runoff eventually build up in surface soils and sub-surface sediments to environmentally critical concentration levels. Thus, on the one hand stormwater infiltration systems may act as effective pollution traps and on the other, they may pose a potential solid waste disposal problem that future stormwater management based on local infiltration will have to face.

Design of a nitrifying tertiary trickling filter based on theoretical concepts

Abstract A nitrification model for a tertiary trickling filter is developed based on stoichiometry, Ficks Law and Monod kinetics. The design of tertiary trickling filters for nitrification is discussed, with special emphasis on: residual ammonium concentration, recirculation, reactors in series, residual alkalinity, residual nitrite concentration and effects of temperature on reactor performance. Wherever possible the theoretical predictions are compared with experimental results.

Nitrification in tertiary trickling filters followed by deep-bed filters

Based on 20 months of pilot experiments, tertiary plastic media trickling filters have shown to be a feasible and cost-saving solution for the enlargement of existing treatment plants for nitrification. The influence of several process variables such as hydraulic load, media characteristics, NH4-load, concentration fluctuations, suspended solids, organic nutrients and biomass grazing on nitrification activity was evaluated. From performance analysis along the trickling filter depth, basic design informations were obtained. In addition to suspended solids removal, subsequent deep-bed filtration proved to be an excellent final treatment to further reduce and stabilize effluent ammonia and nitrite residuals.

Particle characteristics and headloss increase in granular media filtration

Abstract Size density relationships for aggregated particulates in suspension are transferred into a model describing the accumulation of particulate deposits in the pore space of granular media filters. Using data from several shallow filter layer experiments, the deposit density and the actual pore volume occupied by the captured particulates were estimated for solids of different characteristics. Based on extension of existing headloss models, the effects of particulate size, particulate density, filtration rate, and media grain size on headloss development during particle deposition were evaluated.

Size, number and chemical composition of nanosized particles in drinking water determined by analytical microscopy and LIBD

In this paper we comprehensively characterized particles in drinking water originating from a lake water source. We focused on particles smaller than a few hundred nm. Several analytical techniques were applied to obtain information on number concentration, size distribution, morphology and chemical composition of the particles. Morphological information was obtained by atomic force microscopy (AFM) analysis. Two types of particles, spherical aggregates up to a few tens of nm and elongated fibers were identified. Similar structures were also observed in transmission electron microscope (TEM) images. A size distribution of the particles was obtained by applying image analysis (IA) tools on the TEM images. IA results showed an exponential increase of the particle number concentration down to 40 nm, which is the lower detection limit of our setup. The total number of particles down to 10 nm and the average particle diameter were determined with the laser-induced breakdown detection (LIBD) method. The results were in good agreement with the TEM-IA data and showed a total number concentration of roughly 10(8) particles/mL in the purified water. The carbon of the particles was investigated with scanning transmission X-ray microscopy (STXM), which revealed that most particles were organic matter; the C-1s spectra were typical for dissolved organic matter. The methods were applied to characterize the particles from two different drinking waters treated with different methods (conventional vs. ultrafiltration (cut-off 100 kDa)). The results showed that the particle number density following ultrafiltration was lower by a factor of 5-10, compared to conventional treatment. However, the average particle diameter in the finished water of both treatment trains was roughly the same.

Leaching of Biocides from Façades under Natural Weather Conditions

Biocides are included in organic building façade coatings as protection against biological attack by algae and fungi but have the potential to enter the environment via leaching into runoff from wind driven rain. The following field study correlates wind driven rain to runoff and measured the release of several commonly used organic biocides (terbutryn, Irgarol 1051, diuron, isoproturon, OIT, DCOIT) in organic façade coatings from four coating systems. During one year of exposure of a west oriented model house façade in the Zurich, Switzerland area, an average of 62.7 L/m(2), or 6.3% of annual precipitation came off the four façade panels installed as runoff. The ISO method for calculating wind driven rain loads is adapted to predict runoff and can be used in the calculation of emissions in the field. Biocide concentrations tend to be higher in the early lifetime of the coatings and then reach fairly consistent levels later, generally ranging on the order of mg/L or hundreds of μg/L. On the basis of the amount remaining in the film after exposure, the occurrence of transformation products, and the calculated amounts in the leachate, degradation plays a significant role in the overall mass balance.