Direct VUV photodegradation of gaseous α-pinene in a spiral quartz reactor: Intermediates, mechanism, and toxicity/biodegradability assessment

Photodegradation of gaseous α-pinene by a vacuum ultraviolet (VUV) in a spiral reactor was investigated under various gaseous reaction media and residence time, and their respective effects on types and biodegradability of the intermediates were studied. Analysis of carbon amounts showed that about 33% and 43% of total carbon were converted to soluble organic carbon in the air medium with a relative humidity (RH) of 35–40% at empty bed residence times (EBRTs) of 18 and 45 s. Based on the identified intermediates by GC/MS and IC, a photodegradation pathway was proposed by the combined roles of photolysis, OH photooxidation and O3 photooxidation. Biodegradability to active sludge, toxicity to Chlorella vulgaris and 96-well microplates showed that α-pinene could be largely converted to more biodegradable and less toxic compounds through photodegradation in the air reaction medium with a RH of 35–40% at an EBRT of 18 s, in which the initial concentration was 600 mg m−3. Therefore, VUV photodegradation could be applied as an effective pre-treatment method for detoxification and biodegradability improvement under the optimized photodegradation conditions. Such results supported the potential use of VUV photodegradation to improve the removal capacity of conventional biological treatments for hydrophobic and poorly biodegradable compounds.