Performance of two photocatalytic membrane reactors for treatment of primary and secondary effluents

•Treatment of municipal wastewater in two photocatalytic membrane reactors.•Improvement of permeate flux in photocatalysis–ultrafiltration system.•No influence of TiO2 on flux in photocatalysis–membrane distillation system.•Microscopic studies of membrane fouling layer.•Higher quality of permeate in photocatalysis–membrane distillation system.

The performance of two photocatalytic membrane reactors (PMRs), utilizing ultrafiltration (UF) – PMR1, or direct contact membrane distillation (DCMD) – PMR2, during treatment of primary (PE) and secondary (SE) effluents of municipal wastewater treatment plant is presented. Additionally, single UF and DCMD were also examined. TiO2 Aeroxide® P25 (0.5–1.5 g/dm3) was applied as a photocatalyst. Photocatalysis contributed to an improvement of the permeate flux in PMR1 compared to UF alone for 25–38% in case of PE and for 33% when SE were used. Based on SEM, AFM and contact angle measurements the flux improvement was attributed to the porous structure of TiO2 cake and hydrophilicity of the TiO2 – covered membrane. On the opposite, no flux decline during treatment of SE in PMR2 was found. However, in case of PE a decrease of the flux for ca. 40–50%, regardless of the presence or absence of TiO2, was observed. That was due to the formed dense fouling layer, which contributed to the increase of mass and thermal resistances. Permeate quality was higher in PMR2 than in PMR1. However, since mineralization of dissolved organic carbon in feed was very low, the treatment efficiency was attributed mainly to membrane separation rather than to photocatalysis.

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