Novel pebble bed photocatalytic reactor for solar treatment of textile wastewater

A novel, low cost, pebble bed photocatalytic reactor (PBPR) having a horizontal or inclined solar trough collector is presented. The collector contains TiO2 coated, silica rich, white pebbles fixed on a flat surface in an ordered configuration to facilitate the contact between the liquid and the photocatalyst. The reactor efficiency was evaluated for the decolorization of selected reactive dye solutions: Reactive Black 5 (RB5), Reactive Orange 16 (RO16), Reactive Red 2 (RR2), Reactive Red 141(RR141), Reactive Yellow 84 (RY84) and Reactive Violet 13 (RV13) as well as, for the treatment of textile wastewater (synthetic dye house effluents) under sunlight. The rate of decolorization of chlorotriazine reactive dyes was found to be faster than that of vinylsulfone based dyes. The decolorization rate of the dyes followed pseudo first-order kinetics. The first order rate constant of color removal was in the range from 2.479 × 10−2 to 7.858 × 10−2 min−1, with a maximum mineralization efficiency (kTOC/kdye) of 28%. The figure of merit of this reactor as recommended by IUPAC (the collector area per mass ACM) and (the collector area per order ACO) was in the range of 0.30–0.37 m2/g dye and 8.6–12.2 m2/m3/order, respectively, with the exception of RO16 which degraded at a much slower rate. The treatment of simulated textile wastewater showed 72% (Batch I) and 54% (Batch-II) color reduction and 3–35% total organic carbon (TOC) reduction. The results indicate that the PBPR can be successfully used for the decolorization of dyes from dyeing wastewater under sunlight.

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► Novel solar trough collector with TiO2 coated white-pebbles.
► The PBPR treats textile wastewater efficiently.
► Low cost and low maintenance solar photocatalytic reactor.
► Figure of merit comparable with other solar photocatalytic reactors.