Process for filtering a fluid with a compressible filtration media
A high rate, upflow filtration system is described in which a compressible, fibrous lump filtration media is compressed to adjust the porosity and collector size of the media in the bed and to provide a porosity gradient within the bed proceeding from more porous to less porous in a direction opposite to the flow of fluid so that filtration proceeds in a direction from a more porous to a less porous filter bed. Larger particles are removed by the more porous media and successively smaller particles are removed as the filter bed becomes less porous. The system is capable of reducing the turbidity of influent municipal wastewater from about 8 NTU to about 2 NTU at a wastewater flow rate of from about 820 to 1230 L/m 2 ·min (20 to 30 gal/ft 2 ·min), at a bed compression ration of from about 15 to 40 percent, and at a backwash rate of from about 1 to 6 percent based on the total wastewater passing through the filter.
1. A process for filtering a fluid to remove particles therefrom, said process comprising the steps of:
a) passing influent fluid containing particles through a filter bed comprising a compressible filtration media;
b) compressing the filtration media to define a porosity gradient in the filter bed proceeding progressively from more porous to less porous in the direction of the flow of the influent fluid so that filtration proceeds in a direction from a more porous to a less porous filter bed;
c) monitoring head loss across the filter bed;
d) altering the compression of the media during filtration in response to the monitored head loss to reduce head loss and to increase the time between periodic cleanings;
e) withdrawing effluent, and
f) periodically expanding the filter bed while continuing to pass influent fluid containing particles through the filter bed to wash the filtration media.
2. The process of claim 1 wherein the step of altering the compression of the media during filtration comprises maintaining filtration efficiency.
3. The process of claim 2 wherein the step of altering the compression of the media during filtration comprises adjusting the collector size and porosity of the filter media.
4. The process of claim 1 further comprising the steps of monitoring influent fluid quality and adjusting the compression of media during filtration in response to variations in influent quality.
5. The process of claim 1 wherein the filter bed is compressed to a bed compression ratio of up to about 40%.
6. The process of claim 1 wherein the filter bed is compressed to a bed compression ratio of from about 15 to 40%.
7. The process of claim 1 further wherein the filter bed has a porosity of from about 87 to 90% during compression.
8. The process of claim 1 wherein the fluid is passed through the compressed filter bed in accordance with step (b) to establish a filtration flow rate of from about 205 to 2050 L/m2 min (5 to 50 gal/ft2 min).
9. The process of claim 1 wherein the fluid is passed through the compressed filter bed in accordance with step (b) to establish a filtration flow rate of from about 410 to 1640 L/m2 min (10 to 40 gal/ft2 min).
10. The process of claim 1 wherein the fluid is passed through the compressed filter bed in accordance with step (b) to establish a filtration flow rate of from about 820 to 1230 L/m2 min (20 to 30 gal/ft2 min).
11. The process of claim 1 wherein step (b) further comprises establishing a filtration flow rate and step (f) of cleaning the filtration media by periodically expanding the filter bed while continuing to pass influent fluid containing particles through the filter bed comprises passing influent through the expanded bed at a rate of from 1 to 6 percent based on the total fluid passing through the filter.
12. The process of claim 1 wherein step (b) further comprises establishing a filtration flow rate and step (f) of cleaning the filtration media by periodically expanding the filter bed while continuing to pass influent through the filter bed comprises passing influent through the expanded bed at a rate of from about 1 to 3 percent based on the total fluid passing through the filter.
13. The process of claim 1 wherein the influent is a liquid and gas is injected into the liquid while the filter bed is expanded for additional cleaning of the media.
14. The process of claim 1 wherein the influent has a turbidity of up to about 8 NTU and a filtered effluent value of less than about 2 NTU at a flow rate of from about 410 to 1230 L/m2·min (10 to 30 gal/ft3).
15. The process of claim 1 wherein step (e) further comprises recycling the effluent from step (e) for further treatment.
16. The process of claim 1 wherein the fluid is selected from the group consisting of gas, clarified wastewater, machine shop working fluid, hydraulic fluid, oil, and seawater.