Treatment of waters colored with methylene blue dye by vacuum membrane distillation

Textile industries consume large amounts of water and generate highly dye-contaminated effluents. Textile wastewaters have to be treated in order to be recycled in the process or to meet legislative requirements before being discharged. The objective of the present study was to examine the potential use of the vacuum membrane distillation process for the treatment of dyed solutions. Methylene blue (MB) was used as a model dye. Batch experiments were conducted on dilute MB-water mixtures using a tubular polypropylene membrane module. The concentration of MB dye within the feed reservoir was monitored over time. The impact of operating variables such as feed temperature, flow rate and initial dye concentration was investigated. A mathematical model incorporating temperature and concentration polarization effects was developed and validated on the experimental data.

This work demonstrated the ability of VMD to treat wastewaters contaminated with dyes such as MB. The concentration of MB in the feed reservoir and the permeate flux were monitored as feed temperature, feed flow rate, initial NaCl salt concentration were varied. The permeate flow rate decreased exponentially with time. The dye was concentrated in the feed reservoir and was not detected in the permeate. Increasing the feed flow rate significantly affected the flux of the membrane module. The permeate flux was strongly dependent on feed temperature but was independent of salt concentration. The model version that includes the decay of permeate flow rate with time agreed well with the experimental results.