Investigation of quaternary ammonium silane-coated sand filter for the removal of bacteria and viruses from drinking water.

AIMS: To develop an anti-microbial filter media using an attached quaternary ammonium compound (QAC) and evaluate its performance under conditions relevant to household drinking water treatment in developing countries. METHODS AND RESULTS: Silica sand was coated with dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride via covalent silane chemistry. Filter columns packed with coated media were challenged with micro-organisms under different water quality conditions. The anti-bacterial properties were investigated by visualizing Escherichia coli (E. coli) attachment to coated media under fluorescence microscopy combined with a live/dead stain. A 9-cm columns with a filtration velocity of 18 m h(-1) achieved log(10) removals of 1·7 for E. coli, 1·8 for MS2 coliphage, 1·9 for Poliovirus type 3 and 0·36 for Adenovirus type 2, compared to 0·1-0·3 log(10) removals of E. coli and MS2 by uncoated sand. Removal scaled linearly with column length and decreased with increasing ionic strength, flow velocity, filtration time and humic acid presence. Escherichia coli attached to QAC-coated sand were observed to be membrane-permeable, providing evidence of inactivation. CONCLUSIONS: Filtration with QAC-coated sand provided higher removal of bacteria and viruses than filtration with uncoated sand. However, major limitations included rapid fouling by micro-organisms and natural organic matter and low removal of viruses PRD1 and Adenovirus 2. SIGNIFICANCE AND IMPACT OF THE STUDY: QAC-coated media may be promising for household water treatment. However, more research is needed on long-term performance, options to reduce fouling and inactivation mechanisms.

Optimal design of non-Newtonian, micro-scale viscous pumps for biomedical devices.

The present paper addresses the numerical optimization of geometrical parameters of non-Newtonian micro-scale viscous pumps for biomedical devices. The objective is to maximize the mass flow rate per unit of shaft power consumed by the rotor when an external pressure load is applied along the channel that houses the rotor. Two geometric parameters are considered in the optimization process: (i) the height of the channel that houses the rotor (H) and (ii), the eccentricity (epsilon) of the rotor. Three different micro-scale viscous pump configurations were tested: a straight-housed pump (I-shaped housing) and two curved housed pumps (L- and U-shaped housings). The stress-strain constitutive law is modeled by a power-law relation. The results show that the geometric optimization of micro-scale viscous pumps is critical since the mass flow rate propelled by the rotor is highly dependent on epsilon and H. Numerical simulations indicate that mass flow rate is maximized when epsilon approximately 0, namely when the rotor is placed at a distance of 0.05 radii from the lower wall. The results also show that micro-scale viscous pumps with curved housing provide higher mass flow rate per unit of shaft power consumed when compared with straight-housed pumps. The results are presented in terms optimized dimensions of all three configurations (i.e., H(opt) and epsilon(opt)) and for values of the power-law index varying between 0.5 (shear thinning fluids) and 1.5 (shear-thickening fluids).