Dynamic air supply models add realism to the evaluation of control strategies in water resource recovery facilities.

This paper introduces the application of a fully dynamic air distribution model integrated with a biokinetic process model and a detailed process control model. By using a fully dynamic air distribution model, it is possible to understand the relationships between aeration equipment, control algorithms, process performance, and energy consumption, thus leading to a significantly more realistic prediction of water resource recovery facility (WRRF) performance. Consequently, this leads to an improved design of aeration control strategies and equipment. A model-based audit has been performed for the Girona WRRF with the goal of providing a more objective evaluation of energy reduction strategies. Currently, the Girona plant uses dissolved oxygen control and has been manually optimised for energy consumption. Results from a detailed integrated model show that the implementation of an ammonia-based aeration controller, a redistribution of the diffusers, and the installation of a smaller blower lead to energy savings between 12 and 21%, depending on wastewater temperature. The model supported the development of control strategies that counter the effects of current equipment limitations, such as tapered diffuser distribution, or over-sized blowers. The latter causes an intermittent aeration pattern with blowers switching on and off, increasing wear of the equipment.

Nanomaterial transformation and association with fresh and freeze-dried wastewater activated sludge: implications for testing protocol and environmental fate.

Engineered nanomaterials (ENMs) are an emerging class of contaminants entering wastewater treatment plants (WWTPs), and standardized testing protocols are needed by industry and regulators to assess the potential removal of ENMs during wastewater treatment. A United States Environmental Protection Agency (USEPA) standard method (OPPTS 835.1110) for estimating soluble pollutant removal during wastewater treatment using freeze-dried, heat-treated (FDH) activated sludge (AS) has been recently proposed for predicting ENM fate in WWTPs. This study is the first to evaluate the use of FDH AS in batch experiments for quantifying ENM removal from wastewater. While soluble pollutants sorbed equally to fresh and FDH AS, fullerene, silver, gold, and polystyrene nanoparticles' removals with FDH AS were approximately 60-100% less than their removals with fresh AS. Unlike fresh AS, FDH AS had a high concentration of proteins and other soluble organics in the liquid phase, an indication of bacterial membrane disintegration due to freeze-drying and heat exposure. This cellular matter stabilized ENMs such that they were poorly removed by FDH AS. Therefore, FDH AS is not a suitable sorbent for estimating nanoparticle removal in WWTPs, whereas fresh AS has been shown to reasonably predict full-scale performance for titanium removal. This study indicates that natural or engineered processes (e.g., anaerobic digestion, biosolids decomposition in soils) that result in cellular degradation and matrices rich in surfactant-like materials (natural organic matter, proteins, phospholipids, etc.) may transform nanoparticle surfaces and significantly alter their fate in the environment.

Occurrence and removal of titanium at full scale wastewater treatment plants: implications for TiO2 nanomaterials.

Titanium dioxide nanoparticles increasingly will be used in commercial products and have a high likelihood of entering municipal sewage that flows to centralized wastewater treatment plants (WWTPs). Treated water (effluent) from WWTPs flows into rivers and lakes where nanoparticles may pose an ecological risk. To provide exposure data for risk assessment, titanium concentrations in raw sewage and treated effluent were determined for 10 representative WWTPs that use a range of unit processes. Raw sewage titanium concentrations ranged from 181 to 1233 µg L(-1) (median of 26 samples was 321 µg L(-1)). The WWTPs removed more than 96% of the influent titanium, and all WWTPs had effluent titanium concentrations of less than 25 µg L(-1). To characterize the morphology and presence of titanium oxide nanoparticles in the effluent, colloidal materials were isolated via rota-evaporation, dialysis and lyophilization. High resolution transmission electron microscopy and energy dispersive X-ray analysis indicated the presence of spherical titanium oxide nanoparticles (crystalline and amorphous) on the order of 4 to 30 nm in diameter in WWTP effluents. This research provides clear evidence that some nanoscale particles will pass through WWTPs and enter aquatic systems and offers a methodological framework for collecting and analyzing titanium-based nanomaterials in complex wastewater matrices.

Biosorption of nanoparticles to heterotrophic wastewater biomass.

Sorption to activated sludge is a major removal mechanism for pollutants, including manufactured nanoparticles (NPs), in conventional activated sludge wastewater treatment plants. The objectives of this work were to (1) image sorption of fluorescent NPs to wastewater biomass; (2) quantify and compare biosorption of different types of NPs exposed to wastewater biomass; (3) quantify the effects of natural organic matter (NOM), extracellular polymeric substances (EPS), surfactants, and salt on NP biosorption; and (4) explore how different surface functionalities for fullerenes affect biosorption. Batch sorption isotherm experiments were conducted with activated sludge as sorbent and a total of eight types of NPs as sorbates. Epifluorescence images clearly show the biosorption of fluorescent silica NPs; the greater the concentration of NPs exposed to biomass, the greater the quantity of NPs that biosorb. Furthermore, biosorption removes different types of NPs from water to different extents. Upon exposure to 400 mg/L total suspended solids (TSS) of wastewater biomass, 97% of silver nanoparticles were removed, probably in part by aggregation and sedimentation, whereas biosorption was predominantly responsible for the removal of 88% of aqueous fullerenes, 39% of functionalized silver NPs, 23% of nanoscale titanium dioxide, and 13% of fullerol NPs. Of the NP types investigated, only aq-nC(60) showed a change in the degree of removal when the NP suspension was equilibrated with NOM or when EPS was extracted from the biomass. Further study of carbonaceous NPs showed that different surface functionalities affect biosorption. Thus, the production and transformations in NP surface properties will be key factors in determining their fate in the environment.