Filtration, filter ripening

Filter Ripening In water filtration, the process in which deposition of an initial layer of particles causes the filter surface to take on a nature more similar to the particles to be removed. This process enhances the filtering (hence, removal) of the particles. 

Particle concentration and size distribution in raw water have extensive and complex effects on the performance of individual treatment units (flocculator, sedimentation tank, and filter) and on the overall performance of water treatment plants. Mathematical models of each treatment unit were developed to evaluate the effects of various raw water characteristics and design parameters on plant performance. The flocculation and sedimentation models allow wide particle size distributions to be considered. The filtration model is restricted to homogeneous suspensions but does permit evaluation of filter ripening. The flocculation model is formulated to include simultaneous flocculation by Brownian diffusion and fluid shear, and the sedimentation model is constructed to consider simultaneous contacts by Brownian diffusion and differential settling. The predictions of the model are consistent with results in water treatment practice. 

The Standard Plant. The results presented in Figure 9 for the standard treatment plant indicate that effective removal (85% ) of suspended solids is produced by the flocculation-sedimentation process. Filter run length, as indicated by the time it takes to reach a head loss of 250 cm, is 28 hr. Filter ripening is rapid, and essentially complete removal of suspended solids is accomplished by the Alter throughout the run. The settling eflBciency, head loss development, and filtrate quality predicted by the model are consistent with typical water treatment plant performance. 

Figure 10.69. These are automatic filters and are normally used for the first filtration to remove objectionable particles in such a way that the backwash is recycled, thereby reducing waste and extending the life of second stage and other filtration steps used to pohsh the viscose. Because these filters are automatic, there is a significant reduction in the labor required to change and dress filter presses. The filtered viscose is next pumped to a ripening tank.

The temperate and filtrated viscose is fed into the ripening vessels. The viscose is then led over a column under vacuum for de-aeration. Particles that contaminated the viscose during the preceding steps are separated by the second filtration. Usually, metal mats are used as filter material. 

---