Sewage sludge based catalysts for catalytic wet air oxidation of phenol: Preparation, characterisation and catalytic performance

In this study the use of novel CWAO catalysts, namely potentially low cost, sewage sludge derived activated carbons was explored. Two types of municipal sludge were used: dewatered raw filter cake and dewatered mesophilic anaerobically digested sludge. The carbons were produced by: carbonisation: physical activation (steam or CO2) and chemical activation (K2CO3). Hydrochloric acid washing of some of the carbons was also investigated. The carbons were characterised in terms of their surface area, contact pH, propensity towards metal leaching, surface chemistry (via FTIR), ash content and inorganic elemental composition. Their CWAO performance was assessed at 160 degrees C and a partial oxygen pressure of 4.2 bar (25 bar of air) within a stirred batch reactor containing a 5 g/L. phenol solution. All the carbons exhibited catalytic activity, with the K2CO3 activated and HCI washed carbons attaining a phenol and TOC removal that matched the performance of an activated carbon specifically manufactured for oxidative wastewater treatment applications. A strong correlation was found between surface area and phenol or TOC conversion, suggesting that surface area is a primary requisite for their performance in the first batch cycle. Thus, the oxidation of phenol is thought to proceed via a free radical driven mechanism. The active sites necessary to facilitate this mechanism, whether present as surface functional groups or active metals (e.g.. Fe), were detected on all of the sludge based activated carbons. However, no clear correlation between phenol conversion and these active sites could be established. (c) 2010 Elsevier B.V. All rights reserved.