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. 2020 Apr 29;10(5):85.
doi: 10.3390/membranes10050085.

Industrial Wastewater Treatment by Nanofiltration-a Case Study on the Anodizing Industry

Aamer Ali  1 , Maria C Nymann  1 , Morten L Christensen  1 , Cejna A Quist-Jensen  1
Affiliations

Industrial Wastewater Treatment by Nanofiltration-a Case Study on the Anodizing Industry

Aamer Ali et al. Membranes (Basel). .

Abstract

The anodizing industry generates several alkaline and acidic wastewater streams often with high concentrations of heavy metals. In this study, nanofiltration (NF) was used to treat wastewater from individual baths, i.e., wastewater from color rinse, alkaline pickling rinse, acidic pickling rinse and anodizing rinse, as well as a mixture of all the wastewater streams. The experiments were carried out by using a commercial membrane (NF99HF) exhibiting pure water permeability of 10 L/(m2·h·bar). For all wastewater streams except one, pH was adjusted to bring it within the recommended pH limits of the membrane, whereby part of the heavy metals precipitated and was removed. The NF of the color rinse offered high-quality permeate (heavy metals below detection limit) and high permeability (9 L/(m2·h·bar)), whereas the nanofiltration of the alkaline pickling rinse exhibited no permeability. The NF of the acidic pickling rinse showed a permeability of 3.1-4.1 L/(m2·h·bar), but low ion rejection (7%-13%). NF of the neutralized mixed wastewater, after the removal of precipitate, produced high-quality permeate with a stable permeability of 1 L/(m2·h·bar). Treatment of the mixed wastewater is therefore the best option if the water has to be discharged. If the water has to be reused, the permeate conductivity in the color rinse and anodizing rinse baths have been reduced significantly, so the treatment of these streams may then be a better option.

Keywords: anodizing; heavy metals; membranes; nanofiltration; wastewater; water reuse.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Overview of the different solutions treated with nanofiltration (NF).
Figure 2
Figure 2
Schematic overview of the NF system.
Figure 3
Figure 3
Titration curve for some of the wastewater samples.
Figure 4
Figure 4
Permeability during the NF treatment of different baths from the anodizing.
Figure 5
Figure 5
Conductivity of (a) feed and (b) permeate for the different baths.
Figure 6
Figure 6
Rejection of each ion for the different baths. Rejection is not shown for some baths where the concentration of ions is below the detection limit in both the feed and permeate.
Figure 7
Figure 7
Change in concentration of the color rinse bath during filtration.
Figure 8
Figure 8
Absorbance during treatment of the color rinse (measured at 610 nm).
Figure 9
Figure 9
Permeate quality for the different baths.
See this image and copyright information in PMC

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