Nicholas B. Wyatt

Critical conditions for ferric chloride‐induced flocculation of freshwater algae

The effects of algae concentration, ferric chloride dose, and pH on the flocculation efficiency of the freshwater algae Chlorella zofingiensis can be understood by considering the nature of the electrostatic charges on the algae and precipitate surfaces. Two critical conditions are identified which, when met, result in flocculation efficiencies in excess of 90% for freshwater algae. First, a minimum concentration of ferric chloride is required to overcome the electrostatic stabilization of the algae and promote bridging of algae cells by hydroxide precipitates. At low algae concentrations, the minimum amount of ferric chloride required increases linearly with algae concentration, characteristic of flocculation primarily through electrostatic bridging by hydroxide precipitates. At higher algae concentrations, the minimum required concentration of ferric chloride for flocculation is independent of algae concentration, suggesting a change in the primary flocculation mechanism from bridging to sweep flocculation. Second, the algae must have a negative surface charge. Experiments and surface complexation modeling show that the surface charge of C. zofingiensis is negative above a pH of 4.0 ± 0.3 which agrees well with the minimum pH required for effective flocculation. These critical flocculation criteria can be extended to other freshwater algae to design effective flocculation systems. Biotechnol. Bioeng. 2012; 109:493–501.

Polymer Gel Rheology and Adhesion

Polymer gels are found in many applications ranging from foods (Ross-Murphy, 1995; Tunick, 2010) and drug delivery (Andrews & Jones, 2006) to adhesives (Creton, 2003) and consumer products (Solomon & Spicer, 2010). By manipulating the gel’s microstructure, a wide variety of physical properties can be achieved ranging from hard rubbery plastics to soft hydrogels. Silicone-based polymer gels in particular have found wide utilization in consumer products ranging from medical implants to cooking utensils. Here we will discuss methods of characterizing polymer gels using rheological techniques to probe their adhesion and mechanical response. Further, we will link the observed adhesion and mechanical behavior to the gel microstructure.

Growth of mono- and mixed cultures of Nannochloropsis salina and Phaeodactylum tricornutum on struvite as a nutrient source.

The suitability of crude and purified struvite (MgNH4PO4), a major precipitate in wastewater streams, was investigated for renewable replacement of conventional nitrogen and phosphate resources for cultivation of microalgae. Bovine effluent wastewater stone, the source of crude struvite, was characterized for soluble N/P, trace metals, and biochemical components and compared to the purified mineral. Cultivation trials using struvite as a major nutrient source were conducted using two microalgae production strains, Nannochloropsis salina and Phaeodactylum tricornutum, in both lab and outdoor pilot-scale raceways in a variety of seasonal conditions. Both crude and purified struvite-based media were found to result in biomass productivities at least as high as established media formulations (maximum outdoor co-culture yield ∼20±4gAFDW/m(2)/day). Analysis of nutrient uptake by the alga suggest that struvite provides increased nutrient utilization efficiency, and that crude struvite satisfies the trace metals requirement and results in increased pigment productivity for both microalgae strains.

Freshwater Algae Floc Structure in a Shear Flow.

Flocculation is a promising method to overcome the economic hurdle to separation of algae from its growth medium in large scale operations. However, understanding of the floc structure and the effects of shear on the floc structure are crucial to the large scale implementation of this technique. The floc structure is important because it determines, in large part, the density and settling behavior of the algae. Freshwater algae floc size distributions and fractal dimensions are presented as a function of applied shear rate in a Couette cell using ferric chloride as a flocculant. Comparisons are made with measurements made for a polystyrene microparticle model system taken here as well as reported literature results. The algae floc size distributions are found to be self‐preserving with respect to shear rate, consistent with literature data for polystyrene. Three fractal dimensions are calculated which quantitatively characterize the complexity of the floc structure. Low shear rates result in large, relatively dense packed flocs which elongate and fracture as the shear rate is increased. The results presented here provide crucial information for economically implementing flocculation as a large scale algae harvesting strategy. Biotechnol. Bioeng. 2013;110: 3156–3163.

Size and structure of Chlorella zofingiensis/FeCl3 flocs in a shear flow

Flocculation is a promising method to overcome the economic hurdle to separation of algae from its growth medium in large scale operations. However, understanding of the floc structure and the effects of shear on the floc structure are crucial to the large scale implementation of this technique. The floc structure is important because it determines, in large part, the density and settling behavior of the algae. Freshwater algae floc size distributions and fractal dimensions are presented as a function of applied shear rate in a Couette cell using ferric chloride as a flocculant. Comparisons are made with measurements made for a polystyrene microparticle model system taken here as well as reported literature results. The algae floc size distributions are found to be self‐preserving with respect to shear rate, consistent with literature data for polystyrene. Three fractal dimensions are calculated which quantitatively characterize the complexity of the floc structure. Low shear rates result in large, relatively dense packed flocs which elongate and fracture as the shear rate is increased. The results presented here provide crucial information for economically implementing flocculation as a large scale algae harvesting strategy. Biotechnol. Bioeng. 2013;110: 3156–3163.

Multiscale models of nuclear waste reprocessing : from the mesoscale to the plant-scale.

Nuclear waste reprocessing and nonproliferation models are needed to support the renaissance in nuclear energy. This report summarizes an LDRD project to develop predictive capabilities to aid the next-generation nuclear fuel reprocessing, in SIERRA Mechanics, Sandia’s high performance computing multiphysics code suite and Cantera, an open source software product for thermodynamics and kinetic modeling. Much of the focus of the project has been to develop a moving conformal decomposition finite element method (CDFEM) method applicable to mass transport at the water/oil droplet interface that occurs in the turbulent emulsion of droplets within the contactor. Contactor-scale models were developed using SIERRA Mechanics turbulence modeling capability. Unit operations occur at the column-scale where many contactors are connected in series. Population balance models

Cyclic Loading Experiment for Characterizing Foam Viscoelastic Behavior

Several open-cell flexible foams, including aged polyurethane foams, were mechanically characterized over a temperature range of −40 to 20 °C. Quasi-static compression was performed to obtain the stress-strain behavior of the foams. The stress-strain relation is nonlinear, but typically there is a small range of linear behavior initially. Compressive cyclic loading at different amplitudes and frequencies of interest (20–60 Hz) were applied to measure foam’s hysteresis properties, i.e. stiffness and energy dissipation. The cyclic characterization includes foams with different amount of pre-strains, some are beyond the initial linear range as occurred in many applications.