Ceramic Water Filter for Point-Of-Use Water Treatment in Developing Countries: Principles, Challenges and Opportunities

Drinking water source contamination poses a great threat to human health in developing countries. Point-of-use (POU) water treatment techniques, which improve drinking water quality at the household level, offer an affordable and convenient way to obtain safe drinking water and thus can reduce the outbreaks of waterborne diseases. Ceramic water filters (CWFs), fabricated from locally sourced materials and manufactured by local labor, are one of the most socially acceptable POU water treatment technologies because of their effectiveness, low-cost and ease of use. This review concisely summarizes the critical factors that influence the performance of CWFs, including (1) CWF manufacturing process (raw material selection, firing process, silver impregnation), and (2) source water quality. Then, an in-depth discussion is presented with emphasis on key research efforts to address two major challenges of conventional CWFs, including (1) simultaneous increase of filter flow rate and bacterial removal efficiency, and (2) removal of various concerning pollutants, such as viruses and metal(loid)s. To promote the application of CWFs, future research directions can focus on: (1) investigation of pore size distribution and pore structure to achieve higher flow rates and effective pathogen removal by elucidating pathogen transport in porous ceramic and adjusting manufacture parameters; and (2) exploration of new surface modification approaches with enhanced interaction between a variety of contaminants and ceramic surfaces

Understanding the microbiological, organic and inorganic contaminant removal capacity of ceramic water filters doped with different silver nanoparticles

Pathogen removal efficacy of ceramic water filters (CWF) impregnated with silver nanoparticles (nAg) has been well studied, however scarce information is available about the impact of nAg surface functionalization and removal of inorganic and organic pollutants. In this study, we examined the effect of nAg functionalized with casein, maltose and phyto-extracts on the microbiological (Escherichia coli), organic (polycyclic aromatic hydrocarbon, PAH) and inorganic (heavy metals) simultaneous removal using disks manufactured in the laboratory. Results showed that the mass of nAg retained on each disk varied depending on the nanoparticles used (casein-nAg: 80%, maltose-nAg: 93%, and rosemary-nAg: 95%). Untreated CWF disks had a bacterial mass rejection (Rmass) of 95.97%, while nAg impregnated showed values above 99%. Bacteria log removal values (LRV) varied with the type of nanoparticle applied to the disks, rosemary-nAg impregnated disks attained the highest value among all the nAgs tested. In terms of lead removal, non-impregnated Red Art disks had a Rmass of 61%, while the nAg impregnated filters removed 74%, 72%, and 69%, for disks impregnated with casein-nAg, rosemary-nAg, and maltose-nAg, respectively. PAH removal was most effective in unmodified clay (72%), while modified disks had removal of 72% for casein-nAg, 67% for rosemary-nAg, and 69% for maltose-nAg. Mass removal rates of fluorene were determined at 73.38% for unmodified disks, while 74% for casein-nAg, 69% in rosemary-nAg, and 72% in maltose-nAg modified disks. nAg treated disks exhibited no statistical difference in PAH removal when compared to untreated. Application of nAg reduced the amount of culturable bacteria extracted from the surface an interior of the disks compared with unmodified disks. Results show that nAg impregnation increased the removal rates of E. coli and lead in the disks and that nAg average size and size distribution is an important factor in the removal rate of bacteria and lead in CWF

Kinetic, metabolic and macromolecular response of bacteria to chronic nanoparticle exposure in continuous culture

Nanoparticles with antimicrobial properties are used in thousands of nano-enabled consumer products. Therefore, it is important to understand the response mechanisms of bacteria that are exposed to these nanoparticles at different conditions. Moreover, it is necessary to evaluate possible microbial adaptation mechanisms. In our study, Escherichia coli K-12 MG1655 (E. coli) were grown continuously in bioreactors at two specific growth rates (0.1 h-1 and 0.2 h-1) and then exposed to chronic concentrations of casein-coated silver nanoparticles (AgNPs) [1 mg L-1] for about 180 generations. After initiating the injection of AgNPs, the results showed a change in growth kinetic parameters between non-exposed and exposed systems. Maximum yield (Ymax) decreased by 33%, while the maintenance coefficient (ms) increased by 52%. This evidence was indicating the versatility of the culture to growth in the exposed conditions and even the ability to achieve a new stationary state. However, the adaptation was achieved at a metabolic cost. Comparing the concentration and composition of extra-cellular substances that were produced showed differences between the control and exposed conditions, and also between the exposed systems in the two growth conditions. In the AgNPs-exposed bioreactor (EB) growing at 0.1 h-1, AgNPs-ES complexes showed that the ratio of the area representing β-sheets to the area representing α-helix proteins was 2.4, which implies the formation of a protein corona, while at an exposed growth rate of 0.2 h-1 this ratio was \u3c1, indicating no protein corona. Transcriptomic results showed gene regulation in response to AgNPs exposure as a function of the specific growth rate. Batch exposure tests using the resultant cultures for each condition showed a lower inhibitory effect for the AgNPs on EB at 0.1 h-1 than on control bacteria (CB) at 0.1 h-1 in terms of membrane permeation and reactive oxygen species generation. Overall, our study showed that culture growth conditions significantly affects bacterial response to nanoparticle exposure. Therefore, these growth parameters should be determined and reported when performing toxicological tests

Pulse UV light effect on microbial biomolecules and organic pollutants degradation in aqueous solutions

This study present assessed the effect of UV pulsed light (PL) on microbial and organic pollutants using two spiral lamps were used, i.e., PL1 and PL2 lamps, with wavelength cut-offs of 190 and 240 nm, respectively. Overall, our study demonstrated that pulsed UV light impacts several microbial biomolecules and degrades polycyclic aromatic hydrocarbons (PAHs) in aqueous solution. In microbial inactivation by PL2, temporary changes of bacterial cellular components, specifically proteins, were observed, but the compositional changes of bacteria that were exposed to PL1 were permanent due to ozonolysis. PL1 irradiation caused greater deactivation of the bacteria than PL2 irradiation due to the generation of ozone. The higher efficacy of PL1 in terms of membrane disruption, reduction of respiration rate, and reduction of growth rate was due to the production of ozone during the irradiation period. The bacteria that were irradiated with both PL lamps regrew due to photoreactivation, such as an enzymatic DNA-repair mechanism. The PAH degradation kinetics indicate that higher molecular weights degraded faster than those with lower molecular weights. For both lamps, the degradation of naphthalene and fluorene was first order, whereas second order for pyrene and anthracene. Any effect of ozonolysis on the PAH degradation rates was not apparent, which indicated that photolysis was the primary degradation pathway. PAH solutions treated with both pulsed UV lamps did not result in a toxicity effect on the bacteria

Synergistic effects of engineered nanoparticles and organics released from laser printers using nano-enabled toners: Potential health implications from exposures to the emitted organic aerosol

Recent studies have shown that engineered nanoparticles (ENPs) are incorporated into toner powder used in printing equipment and released during their use. Thus, understanding the functional and structural composition and the potential synergistic effects of this complex aerosol and released gaseous co-pollutants is critical in assessing their potential toxicological implications and risks. In this study, toner powder and PEPs were thoroughly examined for the functional and molecular composition of the organic fraction and the concentration profile of 16 Environmental Protection Agency (EPA)-priority polycyclic aromatic hydrocarbons (PAH) using state-of-the-art analytical methods. Results show significant differences in abundance of the non-exchangeable organic hydrogen of toner powder and PEPs, with a stronger aromatic spectral signature in PEPs. Changes in the structural composition of PEPs are indicative of radical additions and free-radical polymerization favored by catalytic reactions, resulting in formation of functionalized organic species. Particularly, accumulation of aromatic carbons with strong styrene-like molecular signatures on PEPs is associated with formation of semi-volatile heavier aromatic species (i.e., PAHs). Further, the transformation of low molecular weight PAHs in the toner powder to high molecular weight PAHs in PEPs was documented and quantified. This may be a result of synergistic effects from catalytic metal/metal oxide ENPs incorporated into the toner and the presence/release of semi-volatile organic species (SVOCs). The presence of known carcinogenic PAHs on PEPs raises public health concerns and warrants further toxicological assessment

Enhancement of surface runoff quality using modified sorbents

The objective of this study was to develop and test nanoparticle-and polymer-based bioactive amended sorbents to enhance stormwater runoff treatment in best management practices (BMPs). Red cedar wood and expanded shale were the sorbents tested. Red cedar wood chips (RC) were modified with 3-(trihydroxysilyl) propyldimethyloctadecyl ammonium chloride (TPA) and silver nanoparticles (AgNPs) at different mass loadings (0.36 mg/g, 0.67 mg/g, and 0.93 mg/g for TPA and 0.33 mg/g and 0.68 mg/g for AgNPs) to simultaneously improve the sorption of organic and inorganic contaminants and pathogenic deactivation in BMPs treating stormwater runoff. Unmodified expanded shale is often used as a filter material for stormwater treatment and was used as a base comparison. The results showed that TPA and AgNPs loading onto red cedar increased the Langmuir maximum sorption coefficient (Q) for polycyclic aromatic hydrocarbons, up to 35 fold and 29 fold, respectively, compared to unmodified red cedar. In the case of heavy metals, Q for lead increased with increased loading of TPA and AgNPs, whereas no significant change in the Q value for cadmium was observed, while zinc and nickel sorption slightly decreased. The Langmuir maximum sorption coefficient of copper was higher for modified red cedar; however, no correlation was observed with TPA or AgNP loadings. The log reduction value (LRV) for Escherichia coli using unmodified red cedar was \u3c1 log, while modified red cedar exhibited LRV up to 2.90 ± 0.50 log for 0.67 mg/g TPA-RC and up to 2.10 ± 0.90 log for 0.68 mg/g AgNP-RC. Although AgNP-modified red cedar shows a comparable performance to TPA-RC, the high cost of production may limit the use of AgNP-amended materials. While TPA-modified red cedar has advantages of lower cost and lower toxicity, the fate, transport, and environmental implications of TPA in natural environments has not been fully evaluated. The findings from this study show that if BMPs were to incorporate the modified red cedar, stormwater treatment of PAH and E. coli could be enhanced, and the quality of the treated water will improve. © 2014 American Chemical Society