Use of the concept of Ive’s Filterability Number (F) to determine the effects of vacuum sludge filtration process

Abstract

The study highlights the laboratory use of the concept of Ive’s filterability number, ‘F’, recently formulated for sand filtration of wastewater. Ive , s Filterability Index Equation was modified and used to investigate the performance of sewage sludge undergoing vacuum filtration process. A simple modified form of Coacklely’s laboratory apparatus has been described for the evaluation of ‘F’. A sludge filtration experiment according to standard procedure suggested by Coackley was mounted. In calculating sludge filterability number and other parameters of the Ive , s equation, vacuum pressures of 20, 16, 12 and 8cmHg were used with the filter medium area of 23.6cm 2 . Four (4) sludge samples of different concentrations obtained from the University of Nigeria, Nsukka treatment plant were prepared. The data generated were used to calculate filterability number F, filtrate volume, V o and instantaneous velocity ‘V i ’, for each filtration cycle. The values of ‘F’ for conditioned sludges were also evaluated from the data using regression analysis. On verification using the experimental data, the theorectical prediction of the modified equation was found to be in consonance with previous findings of other researchers. The filterability index from the generatd data was found to increase numerically with the applied vacuum pressures. Moreover, on verification with Alluminium Sulpahate (Al 3 SO 4 ) on the effects of chemical conditioner on sludge filterability, it was observed that Filterability Index ‘F decreased with increased chemical dosages with the following results: 0.025g/ml, 0.0188g/ml, 0.0130g/ml of Al 3 SO 4 gave corresponding decrease in values of filterability ‘F as 5.764, 5.970 and 6.134 for 0.00259g/Cm 3 sludge sample. Similarly, sludge filterarbility showed an earlier increase with sludge initial solids content and reduced after the solids content was further increased with time, t. Such factors as pressure, initial solid content of sludge and chemical conditioning known to have effects on specific resistance and Sludge Dewaterability Number (SDN) have been found to have corresponding effects on sludge filterability index. These results further enhance the suitability of Ives filterability number concept as a measure of sludge filterability. http://dx.doi.org/10.4314/njt.v37i2.35