Occurrence of human pathogenic viruses in environmental waters (i.e., surface waters, groundwater, drinking water, recreational water, and wastewater) raises concerns regarding the possibility of human exposure and waterborne infections. Presence of virus in water and wastewater is a difficult problem for environmental engineers because of prevalence, infectivity, and resistance of viruses to disinfection. On the other hand, it has been suggested that development of membrane Technology in treating municipal wastewater, such as membrane bioreactors, provides high quality effluents appropriate for water reuse.Removal of human adenovirus 40 (HAdV 40) by hollow fiber ultrafiltration (UF, = 0.04 μm) and microfiltration (MF1, = 0.22 μm; MF2, = 0.45 μm) membranes was elvauted in humic acid (model dissolved species), SiO2 microspheres (model suspended species) and a mix of these constituents. Three separate effects are identified: 1) increased removal due to pore blockage by dissolved species; 2) decreased removal due to cake-enhanced accumulation of viruses near membrane surface; and 3) increased removal by the composite cake acting as a secondary membrane. Comparing to the extent of fouling, feed water composition and membrane pore size together plays more important role in virus removal. Pore blockage improves virus removal while cake formation can either increase or decrease virus removal depending on the relative permeability of the cake.Pressure relaxation and permeate backwash are two commonly used physical methods for membrane fouling mitigation in membrane bioreactor (MBR) systems. In order to assess the impact of these methods on virus removal by MBRs, experiments were conducted in a bench-scale submerged MBR treating synthetic wastewater. The membranes employed were hollow fibers with the nominal pore size of 0.45 μm. The experimental variables included durations of the filtration ( ), pressure relaxation ( ) and backwash ( ) steps. Both pressure relaxation and permeate backwash led to significant reductions in virus removal. For the same value of , longer filtration/relaxation cycles (i.e. larger ) led to higher transmembrane pressure ( ) but did not have a significant impact on virus removal. A shorter backwash ( = 10 min) at a higher flow rate ( = 40 mL/min) resulted in more substantial decreases in and virus removal than a longer backwash ( = 20 min) at a lower flow rate ( = 20 mL/min) even though the backwash volume ( ) was the same. Virus removal returned to pre-cleaning levels within 16 h after backwash was applied. Moderate to strong correlations ( = 0.63 to 0.94) were found between and virus removal.Virus adsorption to sludge particles has been suggested as one of the major mechanisms of virus removal. The results showed that adsorption of HAdV to primary and secondary sludge conformed to Freundlich isotherm, and it exhibited very similar behavior in the two types of sludge. More HAdV was desorbed from primary sludge during sequential desorption experiments, but the difference was not statistically significant. Greater HAdV adsorption was observed when sludge filtrate was used as solute compared to DI water.
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