Treatment of cleaning waters from seawater desalination reverse osmosis membranes for reutilization purposes. Part II: Application of photo-Fenton and photocatalysis processes

This is the second part of the study of cleaning waters from seawater desalination reverse osmosis membranes treatment, with the aim of reclaiming them for reuse. In the first part, Fenton process was applied in these wastewaters and a TOC removal of 67% and a final BOD5 value of 14.8 mg L−1 O2 were achieved by using 4000 mg L−1 of H2O2 and 200 mg L−1 of Fe2+. In this part, photo-Fenton and photocatalysis processes were explored in order to enhance mineralization degree. The highest elimination was achieved with the photo-Fenton process at pH 3, where 79% of TOC removal was obtained with 1400 mg L−1 H2O2 and 70 mg L−1 Fe2+ (3 times lower than in the Fenton process) under solar radiation after 60 min, and 85.6% after 157 min, with the total removal of sodium dodecyl sulfate and obtaining a suitable water for irrigation. This photo-Fenton reaction could also be performed at pH 7, as after 157 min, the same elimination is reached. The addition of P25 accelerates the photo-Fenton process, although after one hour of treatment, similar elimination was reached for both conditions. 77% of TOC removal after 180 min was obtained under solar radiation at pH 3 by adding 1200 mg L−1 of H2O2 with 250 mg L−1 of P25 instead of Fe.