Use of filterability index in granular filtration: effect of filter medium type, size and shape

Ives' Filterability Index (FI) was employed to evaluate silica sand versus crushed recycled glass as a rapid filter media. The presence of past studies comparing these two media allows an evaluation of the applicability and utility of the FI concept as a simple and quick preliminary test for the assessment of different media to be used in water filtration. The present tests also allow an evaluation of the effect of shape on filter performance.

Greywater treatment by granular filtration system using volcanic tuff and gravel media

The main objective of this study was to evaluate the efficiency of a granular filtration system (GFS) in greywater treatment under arid and semi-arid conditions. Six GFSs were designed, constructed, and monitored for approximately 13 months. Each GFS served a single rural Jordanian home by treating their greywater. Volcanic tuff media were used as the filtration media in three of the GFSs while the remaining three GFSs used gravel media. Results show that the biological oxygen demand, chemical oxygen demand, and total suspended solids of the effluent were significantly lower as compared to the influent and demonstrated a removal efficiency of 73%, 65%, and 85%, respectively, when using volcanic tuff media. The removal efficiency was 49%, 51%, and 76%, respectively, when using gravel media. There was a significant increase in the electrical conductivity, pH, potassium (K+), magnesium (Mg2+), chloride (Cl−), sodium (Na+), sulfate (SO42−), bicarbonates (HCO3−), sodium adsorption ratio, and exchangeable sodium percentage in the effluents of the GFS that used volcanic tuff media. The study suggests that GFSs can adequately treat greywater under arid conditions. However, gravel media produce less concentrated effluent compared to the volcanic tuff media.

Impact of granular filtration on ultrafiltration membrane performance as pre-treatment to seawater desalination in presence of algal blooms

To mitigate fouling of the ultrafiltration (UF) membrane and improve permeate quality, we coupled granular filters (GF) with UF membrane as a pre-treatment for reconstituted seawater in the presence of algal bloom. Mono and bilayer granular filtrations were led at a mean velocity of 10 m h−1 over a 7-hour period. Both GF gave the same algal cell retention rate (∼63%) after 7 hours of filtration. Turbidity reduction rate was 50% for the monolayer filter and 75% for the bilayer filter. Resulting organic matter removal rate was 10% for the monolayer filter and 35% for the bilayer filter. Dissolved organic carbon removal was low (20%) with the bilayer filter and non-existent with the monolayer filter. GF-coupled UF reduced humic acids in the permeate (20%) compared with UF alone. Peak pressure of 3 bars was reached at the end of 30 minutes of UF in both direct UF or UF after monolayer GF. The filtrate from the bilayer GF enables UF over a longer period (7 hours).

Impact of kaolinite clay particles on the filtration of Cryptosporidium-sized microspheres

Granular filtration remains a key barrier for Cryptosporidium removal in water treatment plants without UV irradiation. To assess the impact of clay particles in source water on Cryptosporidium removal efficiency by granular filtration, this study investigated the co-transport of Cryptosporidium-sized microspheres and kaolinite particles in sand columns. To investigate the influence of clay load on microsphere transport and deposition, varying influent kaolinite concentrations (0–106particles/mL) and microsphere concentrations (102–106microspheres/mL) were tested. The spatial distribution of retained microspheres was examined subsequent to experiments via filter coring. Results demonstrate that increasing the influent microsphere concentration impaired filter performance due to a blocking mechanism whereby previously retained particles repel incoming particles. In contrast, when the particulate load was dominated by kaolinite (for an equivalent particulate load), filter performance improved as a result of filter ripening whereby previously deposited particles act as additional collectors. Thus, microsphere-kaolinite interactions proved to be favorable although both particles possessed negative zeta potentials in the tested conditions. This study demonstrates that granular filter performance is vulnerable to peak events of microbial contamination. Conversely, Cryptosporidium-sized microsphere removal by granular filtration is enhanced in the presence of kaolinite in source water.