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

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/Fe2+) and photo-Fenton (UV/H2O2/Fe2+) 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.