Characterizing the efficiency of low-cost LED lights for conducting laboratory studies to investigate polycyclic aromatic hydrocarbon photodegradation processes

Marieh Arekhi; Leigh G Terry; T Prabhakar Clement

doi:10.1016/j.envres.2022.114951

Characterizing the efficiency of low-cost LED lights for conducting laboratory studies to investigate polycyclic aromatic hydrocarbon photodegradation processes

Environ Res. 2023 Jan 15:217:114951. doi: 10.1016/j.envres.2022.114951. Epub 2022 Nov 25.

Authors

Marieh Arekhi¹, Leigh G Terry¹, T Prabhakar Clement²

Affiliations

¹ Department of Civil, Construction and Environmental Engineering, The University of Alabama, Tuscaloosa, AL, USA.
² Department of Civil, Construction and Environmental Engineering, The University of Alabama, Tuscaloosa, AL, USA. Electronic address: pclement@ua.edu.

PMID: 36436555
DOI: 10.1016/j.envres.2022.114951

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are common contaminants ubiquitously present in various waste products such as biosolids (e.g. wastewater sludges), oil spill residues (e.g. tarballs), road asphalts, and combustion byproducts. In this study, the photodegradation of PAHs is investigated under natural sunlight (cloudy and sunny/clear weather conditions), and using two types of artificial LED light sources. This is the first study to investigate the relative efficiency of low-cost LED light sources for conducting laboratory-scale PAH photodegradation experiments and directly comparing the results against those obtained using natural sunlight. Two types of LED light sources are investigated in this study: a light source with a full-spectrum range (380 nm-780 nm) that can cover the broad wavelength range of solar light reaching the Earth's surface, and a light source with a UV-A range (365 nm) that covers the UV range of the solar spectrum reaching the Earth's surface. The results show that the degradation of high molecular weight (HMW) PAHs is primarily due to photodegradation, and other lighter PAHs are degraded by both photodegradation and evaporation processes. HMW PAH photodegradation reactions follow the first-order degradation kinetics. The degradation rate constants of different PAHs are used to compare the relative efficiency of the light sources. The data show that the full-spectrum LED induced PAH photodegradation rates are similar to the natural sunlight induced rates. Furthermore, when the values of the rate constants are normalized to respective irradiance levels, the normalized rates for HMW PAH photodegradation under both full-spectrum LED light and natural sunlight are almost identical. However, the normalized photodegradation rate constants of HMW PAHs under the UV-A LED light are about two to three orders of magnitude higher than the sunlight as well as the full-spectrum-LED values. Therefore, the UV-A LED light is the optimal low-cost light source for studying PAH photodegradation processes under laboratory conditions.

Keywords: First-order kinetics; High molecular weight PAHs; LED light; PAHs; Photodegradation; UV-A light.

Publication types

Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Kinetics
Photolysis
Polycyclic Aromatic Hydrocarbons* / chemistry
Sunlight
Ultraviolet Rays

Substances

Polycyclic Aromatic Hydrocarbons