Dilute Flow Filtration

June 25, 1999

Recently we tested the Fiber Filter at Liberty Paper in Becker, Minnesota. This is a modern OCC (Old Corrugated Container) recycle mill. Rated at 300 tons per day, the mill specializes in producing linerboard. The test machine was a FF-6, the smaller version of the FF-12 machine that would be required to satisfy the mill loading.

We were working with dilute feed flows, .02% to 0.20% solids consistency, and remarkable success was experienced. The results broaden the market for Fiber Filters from deinking to include most recycle paper mills.

The applications tested were (a) filtering press liquor from Vincent screw presses that are used on the mill wastewater stream; (b) filtering the flow of wastewater ahead of the clarifier; and (c) filtering the final wastewater flow that goes into the city sewer system.

Feed:  Press Liquor from Vincent VP-16's screw presses.  These are used on the mill wastewater stream after it has been across sidehill screens.
          Feed:          .06% consistency      620 ppm TSS *
          Filtrate:      .02% consistency      330 ppm TSS *
          Cake/Sludge:  3.0% consistency

Clarifier Feed Chest
          This includes sidehill screen filtrate, press liquor, and other waste streams.
          Feed:          .15% consistency   1,970 ppm TSS *
          Filtrate:      .04% consistency     460 ppm TSS *
          Cake/Sludge:  4.1% consistency

These two tests were run with an 86 micron sleeve in the FF-6, very high elevation adjustment, 30 to 60 gpm, no VFD.

* The differences between percent solids consistency and parts per million of total suspended solids arise from using two different laboratory procedures for measuring the same thing.

We also ran tests on the city sewer flow. The results were surprising:

City Sewer Water:

    • Feed: 204 ppm
    • Filtrate: 148 ppm

This test was run with a 43 micron sleeve, very high elevation adjustment, 90 to 120 gpm. Their normal flow is 400 gpm, so a FF-12 may carry it all with a 31 micron screen. The cake/sludge we collected had sand and grit, with some fiber.

The cake/sludge from the Fiber Filter would be fed back into the screw presses.

Two alternate projects are being reviewed for potential financial justification:

    • Filtration of clarifier feed so as to reduce polymer consumption in the clarifier.
    • Filtration of final flow to the city sewer so as to reduce sewer surcharges.

Issue 95