Purification of household greywater loaded with hair colorants by solar photocatalysis using TiO2-coated textile fibers coupled flocculation with chitosan

• Efficient treatment of greywater by solar photocatalysis using TiO2–chitosan film.
• Chitosan dissolved during treatment and acted as flocculant for residual organics.
• Ti(III) species were found in developed film.
• Toxicity, COD, BOD5, concentration of surfactants, dyes and emulsifiers reduced.
• Kinetic model for greywater mineralization was proposed.

This study reports a possibility of the household greywater treatment by solar photocatalysis followed by flocculation with special emphasis on hair colorants and accompanying chemicals. The greywater of concern (hereafter: GW) was collected from the bathroom after hair dyeing, washing and rinsing. Its tentative composition was determined taking into account listed ingredients of used hair colorant, dyeing chemistry and measured values of surface tension, light absorption and scattering. In order to assess the quality of the effluent, TOC, COD, BOD5 and toxicity toward yeast and Vibrio fischeri were determined. Greywater was treated in the hand-made reactor system, with a constant recirculation over photocatalytic layer exposed to direct sunlight. Photocatalytic layer consisted of TiO2-coated textile fibers prepared by applying TiO2–chitosan pasteous dispersion on polyester/wool blend textile (75% polyester, 25% wool). Results showed the significant decrease in organic content, COD and toxicity over a period of 4 h. UV–vis spectra of treated samples indicate the complete degradation of dye molecules and certain aromatic compounds. Emulsifying compounds and surfactant concentrations were reduced significantly. Preliminary kinetic study involving chitosan dissolution kinetics and pollutant mineralization was presented. It was observed that chitosan dissolved at certain extent during photocatalytic treatment, thus acted as an efficient flocculant in treated wastewater; flocs were observed shortly after photocatalytic treatment, followed by complete sedimentation over a period of 12 h in dark. Additionally, surface of the photocatalytic layer was analyzed by TGA, FTIR, ESR and Raman spectroscopy, SEM and contact angle measurements. Evidence of Ti (III) species was presented.

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