Pilot plant scale reactive dyes degradation by solar photo-Fenton and biological processes

Solar photo-Fenton reactions as a stand-alone process and as a pre-treatment of an aerobic biological treatment for Procion Red H-E7B and Cibacron Red FN-R reactive dyes degradation have been carried out at pilot plant scale. Photo-Fenton oxidation was conducted using a Compound Parabolic Collector (CPC) solar photo-reactor and the biological treatment was carried out with an Immobilised Biomass Reactor (IBR). Artificial light photo-Fenton experiments carried out at laboratory scale have been taken as starting point. When applying photo-Fenton reaction as a single process, 10 mg L−1 Fe (II) and 250 mg L−1 H2O2 for 250 mg L−1 Procion Red H-E7B treatment, and 20 mg L−1 Fe (II) and 500 mg L−1 H2O2 for 250 mg L−1 Cibacron Red FN-R treatment closely reproduced the laboratory mineralisation results, with 82 and 86% Dissolved Organic Carbon (DOC) removal, respectively. Nevertheless, the use of sunlight with the CPC photo-reactor increased the degradation rates allowing the reduction of Fe (II) concentration from 10 to 2 mg L−1 (Procion Red H-E7B) and from 20 to 5 mg L−1 (Cibacron Red FN-R) without yield loses. Carboxylic acids, SO42−, NH4+ and NO3− generation was monitored along with dye mineralisation. Finally, in the combined photo-Fenton/biological system, reagents doses of 5 mg L−1 Fe (II) and 225 mg L−1 H2O2 for Cibacron Red FN-R and 2 mg L−1 Fe (II) and 65 mg L−1 H2O2 for Procion Red H-E7B were enough to generate biodegradable solutions that could be fed to the IBR, even improving bench-scale results.