Quantitative Understanding of Nanoparticle Flocculation in Water Treatment

Flocculation is critical in drinking water treatment; in flocculation, the particle size distribution changes from a large number of small particles to a small number of larger particles. Larger particles are effectively removed by settling and filtration processes that follow flocculation. In recent years, manufacturing of engineered nanoparticles has skyrocketed, and these nanoparticles can enter our water supplies, but knowledge of their fate in water treatment is limited. The objective of this research was to update knowledge of flocculation by extending previous work at the microscale to the nanoscale. Flocculation involves transport of particles to the vicinity of one another and subsequent attachment if interactions at close distances are favorable. Transport and possible collisions are brought about by Brownian motion, differential sedimentation, and fluid shear; these processes, even at the nanoscale, are well understood. Whether collisions and attachment actually occur, however, depend on a balance of hydrodynamic interactions, van der Waals attraction, and electrostatic repulsion; this research quantitatively assessed, for the first time, this balance for collisions of nanoparticles by all three collision mechanisms using a well-established trajectory analysis approach. The collision efficiency (α) is the ratio of the number of successful collisions (attachment) to the number of collisions predicted by the transport equations. The analysis was performed with and without electrostatic repulsion, which occurs if particles are charged. In all cases, Brownian motion was the dominant flocculation mechanism. However, without electrostatic repulsion, differential sedimentation and fluid shear were found to be far more important than heretofore expected because the α value can be substantially higher than one, contrary to all previous understanding. With electrostatic repulsion, collisions by these two mechanisms were found to occur only if the particles are substantially different in size. Experiments in which the changes in particle size distributions of nanoparticles were carefully monitored were also performed, and the results compared to the mathematical predictions. Although not perfect, excellent agreement between the measured and predicted particle size distributions was found. The conclusion is optimistic: if nanoparticles are properly destabilized to reduce or eliminate surface charge, they will be well removed in conventional water treatment plants

The (relative) insignificance of G revisited to include nanoparticles

The collision efficiency functions, α(i,j), of two colliding particles for the three operative transport mechanisms in flocculation (Brownian motion [Br], fluid shear [Sh], and differential sedimentation [DS]) were numerically calculated over a broad size range (including nanoparticles). All computations include the hydrodynamic force and van der Waals (vdW) attraction, while the effects of electrical double‐layer repulsive forces were investigated by their exclusion or inclusion. Flocculation of nanoparticles should be extremely rapid if they are uncharged but will be dramatically reduced when substantially charged. For small neutral particles, α(i,j) values could be greater than those obtained during Sh and DS as vdW attraction outweighs the (negative) hydrodynamic effects. Overall, the results confirm the findings of an earlier article, that Br is the dominant flocculation mechanism when at least one particle is small (\u3c1 μm in diameter), Sh is only dominant when both particles are greater than 1 μm and the ratio of the two particle sizes is less than 10, and DS is dominant in all other cases. Flocculators should be operated with low‐velocity gradient (G) values (in the range of 10–20 s−1), with only sufficient mixing to keep particles in suspension, but proper particle destabilization is essential for effective flocculation

Experiment on Activated Carbon Manufactured from Waste Coffee Grounds on the Compressive Strength of Cement Mortars

In this paper, we performed an experiment with activated carbon manufactured from waste coffee grounds on the compressive strength of normal cement mortars. The activated carbon reinforcement was manufactured from waste coffee grounds, and the collected coffee grounds were then transformed into activated carbon granules through the physical activation process. The activated carbon/cement composites were prepared by mixing cement with activated carbon granules with the weight fractions of 0.5%, 1%, 1.5%, 5%, and 10% cement. The experimental results show that adding activated carbon up to 1.5 wt% increased the early strength of cement mortars. Furthermore, we found that the composites incorporated with a small amount of activated carbon (≤1.5 wt%) had higher compressive strength over the curing period than the normal cement without activated carbon. We believe that these results would potentially have commonalities with morphological symmetry phenomena that occur on the surfaces of activated carbon granules

Hospital Vozandes del Oriente Wastewater Treatment System Design

Shell is a town located in the Eastern foothills of the Ecuadorian Andes approximately 94 miles Southeast of Quito. Hospital Vozandes del Oriente (HVO) is a hospital located in Shell owned and operated by Hoy Cristo Jesús Bendice (HCJB) Global. HCJB is a non-profit mission organization committed to Biblical values and community development principles. Pure Pastaza, a senior design team from Calvin College, in conjunction with HCJB, has designed a wastewater treatment system for HVO. The design promotes the protection of human and environmental health by providing a sustainable solution to wastewater treatment and sets an example of stewardship to the surrounding community. The existing wastewater treatment system for the hospital property includes a pipe network and collection system leading to an undersized septic tank. As no drainfield or secondary treatment exist, effluent from the septic tank passes directly into the Motolo River south of the hospital without receiving additional treatment. There is also no appropriate method or suitable location established for septage disposal, which has consequently been disposed of directly in the river. The hospital has therefore requested the design of an alternative method of wastewater treatment and disposal of the sludge produced. Various treatment alternatives have been analyzed and compared from a standpoint of stewardship and cultural appropriateness. Pure Pastaza is recommending significant modifications to the existing septic system. The design utilizes an additional septic tank in series with the original, a dosing tank and a drain field. This design has been chosen due to its simplicity and relatively low maintenance. The sludge will be disposed of through on site burial techniques

Polymer-Capped Nanoparticle Transport in Granular Media Filtration: Deviation from the Colloidal Filtration Model

The single-collector removal efficiency based on the colloidal filtration model is widely used to quantify deposition of nanoparticles in porous media filtration. The validity of this theory for nanoparticles, especially at filtration rates used in water treatment, was evaluated. Granular media filtration experiments were performed under widely variant physical conditions. Chemical effects were minimized by selecting spherical branched polyethylenimine capped silver nanoparticles as a positively charged nanoparticle to avoid electrostatic repulsion with the negatively charged silica filter media. The model and experimental results agreed well for 50 and 100 nm particles, but 10 nm particles were removed to a lesser extent than the model predicted. An updated Derjaguin-Landau-Verwey-Overbeek calculation was performed for the interaction energy between polymer-capped nanoparticles and the collector surface, under constant potential, constant charge, and mixed assumptions. The effect of particle size on these calculations was dramatic, leading to far less attractive energy for the smallest particles in the mixed case, and even repulsion in the constant charge case. These revised calculations are the primary means to explain the unexpected data

Quantifying surface morphology of manufactured activated carbon and the waste coffee grounds using the Getis-Ord-Gi* statistic and Ripley’s K function

Activated carbon can be manufactured from waste coffee grounds via physical and/or chemical activation processes. However, challenges remain to quantify the differences in surface morphology between manufactured activated carbon granules and the waste coffee grounds. This paper presents a novel quantitative method to determine the quality of the physical and chemical activation processes performed in the presence of intensity inhomogeneity and identify surface characteristics of manufactured activated carbon granules and the waste coffee grounds. The spatial density was calculated by the Getis-Ord-Gi* statistic in scanning electron microscopy images. The spatial characteristics were determined by analyzing Ripley’s K function and complete spatial randomness. Results show that the method introduced in this paper is capable of distinguishing between manufactured activated carbon granules and the waste coffee grounds, in terms of surface morphology

Comprehensive understanding of nano-sized particle separation processes using nanoparticle tracking analysis

Understanding of nano-sized particle separation processes has been limited by difficulties of nanoparticle characterization. In this study, nanoparticle tracking analysis (NTA) was deployed to evaluate the absolute particle size distributions in laboratory scale flocculation and filtration experiments with silver nanoparticles. The results from NTA were consistent with standard theories of particle destabilization and transport. Direct observations of changes in absolute particle size distributions from NTA enhance both qualitative and quantitative understanding of particle separation processes of nano-sized particles

Azo-Dye-Functionalized Polycarbonate Membranes for Textile Dye and Nitrate Ion Removal

Challenges exist in the wastewater treatment of dyes produced by the world’s growing textiles industry. Common problems facing traditional wastewater treatments include low retention values and breaking the chemical bonds of some dye molecules, which in some cases can release byproducts that can be more harmful than the original dye. This research illustrates that track-etched polycarbonate filtration membranes with 100-nanometer diameter holes can be functionalized with azo dye direct red 80 at 1000 µM, creating a filter that can then be used to remove the entire negatively charged azo dye molecule for a 50 µM solution of the same dye, with a rejection value of 96.4 ± 1.4%, at a stable flow rate of 114 ± 5 µL/min post-functionalization. Post-functionalization, Na+ and NO3− ions had on average 17.9%, 26.0%, and 31.1% rejection for 750, 500, and 250 µM sodium nitrate solutions, respectively, at an average flow rate of 177 ± 5 µL/min. Post-functionalization, similar 50 µM azo dyes had increases in rejection from 26.3% to 53.2%. Rejection measurements were made using ultraviolet visible-light spectroscopy for dyes, and concentration meters using ion selective electrodes for Na+ and NO3− ions

Silver nanoparticle removal from drinking water: Flocculation/sedimentation or filtration?

Silver nanoparticles are used in a wide variety of consumer products and are therefore rapidly becoming ubiquitous in the natural environment; they can be expected to be found in the natural waters used as drinking water supplies. This research investigated whether such particles could be expected to be removed in conventional water treatment plants such as flocculation and filtration. Both flocculation and granular media filtration experiments with citrate-capped silver nanoparticles were performed at different ionic strengths and in the presence and absence of natural organic matter. The results were generally consistent with theories of particle destabilization that have been developed for larger particles (greater than 1 mm), suggesting that silver nanoparticles are likely to be removed in conventional treatment processes

Plasma amyloid-β oligomerization assay as a pre-screening test for amyloid status

Objective We assessed the performance of plasma amyloid oligomerization tendency (OAβ) as a marker for abnormal amyloid status. Additionally, we examined long-term storage effects on plasma OAβ. Methods We included 399 subjects regardless of clinical diagnosis from the Amsterdam Dementia Cohort and European Medical Information Framework for AD project (age, 63.8 ± 6.6; 44% female). Amyloid status was determined by visual read on positron emission tomography (PET; nabnormal = 206). Plasma OAβ was measured using the multimer detection system (MDS). Long-term storage effects on MDS-OAβ were assessed using general linear models. Associations between plasma MDS-OAβ and Aβ-PET status were assessed using logistic regression and receiver operating characteristics analyses. Correlations between plasma MDS-OAβ and CSF biomarker levels were evaluated using Pearson correlation analyses. Results MDS-OAβ was higher in individuals with abnormal amyloid, and it identified abnormal Aβ-PET with an area under the curve (AUC) of 0.74 (95% CI, 0.67–0.81), especially in samples with a storage duration < 4 years. Combining APOEe4 and age with plasma MDS-OAβ revealed an AUC of 81% for abnormal amyloid PET status (95% CI, 74–87%). Plasma MDS-OAβ correlated negatively with MMSE (r = − 0.29, p < .01) and CSF Aβ42 (r = − 0.20, p < 0.05) and positively with CSF Tau (r = 0.20, p = 0.01). Conclusions Plasma MDS-OAβ combined with APOEe4 and age accurately identifies brain amyloidosis in a large Aβ-confirmed population. Using plasma MDS-OAβ as a screener reduced the costs and number of PET scans needed to screen for amyloidosis, which is relevant for clinical trials. Additionally, plasma MDS-OAβ levels appeared affected by long-term storage duration, which could be of interest for others measuring plasma Aβ biomarkers.The Alzheimer Center Amsterdam is supported by Stichting Alzheimer Nederland and Stichting VUmc fonds. Research of the Alzheimer center Amsterdam is part of the neurodegeneration research program of Amsterdam Neuroscience. The clinical database structure was developed with funding from Stichting Dioraphte. The VUmc Biobank is supported by VUmc. The research leading to these results has received support from the Innovative Medicines Initiative Joint Undertaking under EMIF grant agreement no. 115372, resources of which are composed of financial contribution from the European Unions Seventh Framework Programme (FP7/2007-2013) and EFPIA companies in kind contribution