Decolouration of H₂SO₄ leachate from phosphorus-saturated alum sludge using H₂O₂ and advanced oxidation processes in phosphorus recovery strategy

Abstract

As a part of attempt for phosphorus (P) recovery from P-saturated alum sludge, which was used as a low-cost P-adsorbent in treatment reed bed for wastewater treatment, decolouration of H₂SO₄ leachate obtained from previous experiment, possessing a great deal of P, aluminum and red-brown coloured materials (RBCMs), by using H₂O₂ and advanced oxidation processes (AOPs) was investigated. The use of H₂O₂ and AOPs in the forms of Fenton (H₂O₂/Fe^{2 +}) and photo-Fenton (UV/H₂O₂/Fe^{2 +}) were tested. The changes in colour and total organic carbon (TOC) were taken place as a result of mineralization of RBCMs. The results revealed that all of these three processes examined were efficient. It was found that about 98% colour and 47% TOC can be removed under photo-Fenton treatment after 8 hours of UV irradiation.Correspondingly, the reaction rates of H₂O₂ and Fenton systems were slow, but 100% colour and 59% TOC removal of H₂O₂ process and 100% colour and 67% TOC reductions of Fenton process can be achieved after 72 hours of reaction. The changes of structure and molecular weight/size of RBCMs were also evaluated by HPLC and UV-vis spectroscopic analysis. From the results, some chromophores of RBCMs such as aromatic groups were appeared to be easily degraded to the smaller refractory components. Hence, based on the experimental results and considering the investment and expediency of operation, H₂O₂ and Fenton oxidation could be suitable technologies for the treatment of the RBCMs derived from P-extraction stage by using H₂SO₄ leaching.

Keywords:

• Natural organic matter
• peroxide
• advanced oxidation process
• Fenton reaction
• colour
• total organic carbon

Acknowledgments

The authors wish to acknowledge the research funding provided by the Environmental Protection Agency, Ireland through the Environmental Technologies Scheme (project no. 2005-ET-MS-38-M3). The first author would like to thank University College Dublin for the Ad Astra scholarship. Mr. Patrick Kearney, Section head technician, Water and Effluents Laboratory, UCD, is also thanked for his invaluable assistance.