Peroxymonosulfate–Co(II) oxidation system for the removal of the non-ionic surfactant Brij 35 from aqueous solution

The non-ionic surfactant Brij 35 was effectively removed from concentrated aqueous solution by the peroxymonosulfate/Co(II) system, using oxone (2KHSO5·KHSO4·K2SO4) as a source of peroxymonosulfate. At pH = 2.3 and initial Brij 35 concentration in the range 680–2410 mg L−1, 86–94% removal was achieved after 24 h, using Co(II) = 15 μM and oxone = 5.9 mM. The effectiveness of removal did not change when initial pH was in the range 2.3–8.2. After five subsequent additions of Co(II) and oxone to the solution, COD and TOC removals increased up to 64% and 33%, respectively. Radical quenching tests confirmed that sulfate radical was the dominant radical species in the system. The main identified by-products from surfactant degradation were: (a) low molecular weight organic acids; (b) aldehydes and formates with shorter ethoxy chain than Brij 35; (c) alcohol ethoxylates carrying hydroxyl groups bonded to ethoxy chain. By-products identification allowed to hypothesize the pathways of Brij 35 degradation.

► The peroxymonosulfate/Co(II) system effectively removed a non-ionic surfactant from aqueous solution.
► Sulfate radicals were the dominant radical species in the investigated system.
► Oxidation by-products were identified and degradation pathways for non-ionic surfactants were outlined.