Slow granular filtration for water reuse

The slow sand filtration (SSF) design parameters as known for purifying surface water cannot be copied for the treatment of secondary effluents. The objectives of the present research were to examine the possibility of slow granular filtration (SGF) as advanced treatment of secondary effluents for reuse purposes and examine filter performance under various design regimes. Slow granular filtration runs where made with four different filters at rate of 0.15 m/h. 0.6 mm, 0.25 mm sand or tuff grains or their combination were used. Grain size of 0.25 mm gave low impurities concentration in the effluent but short filtration runs. Double layer bed caused longer filtration run as well as lower impurities concentration in the effluent. Combining the tuff as the top bed layer caused longer filtration run, probably due to the morphologic and chemical properties of the tuff. The water column above the bed plays an important role in the filtration process. Intense microbiologic activity in the column changes the TSS and COD concentration as well as the availability of the biodegradable matter. The dissolved oxygen concentration in the water column above the bed, and in the bed depth can serve as a good indicator for ripening of the biological layer.