Recycling of industrial waste water by using a two-step nanofiltration process for the removal of colour

One of the production facilities of Akzo Nobel Chemicals produces a low pH very dilute aqueous waste stream, containing one or more coloured components and an organic component at saturation concentration. Due to the presence of colour it is not possible to recycle this aqueous stream to the production process and is currently disposed of at high costs. However, a two-step nanofiltration process has been developed, which is able to recover 90% of the waste stream and to reduce the colour content with 99.8%. The estimated payback time is 3 years. This paper describes the results of the laboratory- and bench-scale tests in Arnhem as well as the results of the pilot-scale tests, which were performed on site.

Based on the results of the pilot-scale experiments full-scale process designs were made for a one-step process, as well as a two-step process (Fig. 7). A one-step process (using tubular membranes) is able to recover 90% of the waste stream and to reduce the colour content with 93%. By adding a second step (using spiral wound membranes), the colour reduction can be increased up to 99.8%. The payback time for the two-step process is estimated to be 3 years. The trials have shown that both a one-step nanofiltration process using tubular membranes and a two-step nanofiltration process, using tubular membranes for the first step and spiral wound membrane elements for the second step, are technical and economical feasible solutions for colour removal from a low pH dilute aqueous waste water stream containing an organic component at its saturation concentration. In order to make a decision whether a one-step process, Permeate Step 1 (99%, 340 APHA) Feed (100%, 5000 APHA) Recycle Stream (89%, 8 APHA) Waste stream (11%, 44940 APHA) Step 1: Tubular membranes Step 2: Spiral wound membranes Fig. 7. Process design of the two-step process.