Sewage sludge based carbons for catalytic wet air oxidation of phenolic compounds in batch and trickle bed reactors

The potential of using sludge based activated carbons (SBACs) for catalysing the wet air oxidation (WAO) of phenol, o-cresol, o-chlorophenol and p-nitrophenol was assessed in both a batch slurry reactor and a continuous trickle-bed reactor. In the batch reactor, the activity of two powdered carbons prepared from, respectively, dewatered raw (DRAW) sludge and dewatered, mesophilic anaerobically digested (DMAD) sludge was tested at 160 °C and 4.2 bar of oxygen partial pressure. Continuous, trickle-bed reactor experiments of up to 72 h were conducted at similar operating conditions to study the durability and catalytic wet air oxidation (CWAO) performance of three economically promising steam activated SBACs. Due to their low mechanical strength, the two DRAW derived SBACs tested were produced using two different attrition resistance enhancement techniques. A commercial activated carbon (Chemviron, AP4-X) was employed as the reference catalyst for all of the tests.In the batch runs, the SBACs and AP4-X achieved high levels of pollutant conversion in the case of phenol, o-cresol and o-chlorophenol. However, irrespective of the carbon tested, p-nitrophenol was resistant to oxidation. When employed in the trickle-bed reactor, the DRAW derived SBAC pelletised using a lignosulphonate binder was found to be the most stable carbon. With this carbon the order of compound reactivity was as observed in the batch experiments.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Sewage sludge based activated carbons (SBACs) were prepared for wet air oxidation (WAO). ► The SBACs were viable catalysts for the WAO of phenol, o-cresol and o-chlorophenol. ► The p-nitrophenol molecule was resistant to SBAC catalysed WAO. ► Using CWAO to destroy o-chlorophenol requires a corrosion resistant reactor. ► A hardened SBAC with a high stability was produced using a lignosulphonate binder.