Treatment of wastewater from an alkaline cleaning solution by combined coagulation and photo-Fenton processes

A coupled coagulation and photo-Fenton treatment has been applied to an industrial wastewater coming from the use of an alkaline cleaning solution. The real wastewater contained anionic and nonionic surfactants, tripolyphosphate, soda ash, metasilicate and oil residuals. After the proposed treatment, the wastewater fulfilled Argentine regulations for sewage discharge (10 mg/L total phosphorus, 0.7 g/L COD). First, phosphorous was eliminated by coagulation with FeSO4 and then COD was removed by a photo-Fenton treatment. The dark Fenton treatment was also effective to remove COD but it did not allow achieving the discharge regulations, and the application of light was needed. The photo-Fenton treatment showed to be very effective to treat this particular wastewater in 2 h and with a high efficiency of H2O2 consumption. The experiments performed at bench scale allowed to propose a scheme for the in situ treatment of the alkaline cleaning solution wastewater, which could be extended to other similar wastewaters.