A dual approach using UV irradiation and subcritical water extraction for enhanced PLA waste degradation in a bioaugmented food composter

Abstract

Polylactic acid (PLA) ranks among the most extensively produced bioplastics, raising waste management concerns globally. This study explored dual pretreatment strategies, specifically photolysis by Ultraviolet-C (UVC) and hydrolysis by subcritical water extraction (SWE), for PLA waste treatment. UVC irradiation reduced the mechanical strength and viscosity average molecular weight (Mv) of PLA, but the effects were more significant in thin PLA films than in thick PLA beverage cups. Thus, the PLA cups were selected for SWE treatment, which reduced their Mv from 190,000 to 5300. The pulverized SWE-treated PLA was later used for inducing protease and esterase in PLA-degrading bacterial consortium EAc. This active inoculum was applied as a bioaugmentation agent in a food composter for degrading UVC-treated PLA cups with food waste. PLA weight loss in the bioaugmented food composter (42 %) after 56 days was greater than the naturally attenuated composter (1 %). The residual PLA in the final bioaugmented compost had a relatively smaller size and lower Mv with prominent surface erosion. In addition, the 16S rRNA gene amplicon sequencing revealed that the bioaugmentation promoted bacterial diversity and community interactions. Conclusively, PLA waste can be treated by UVC irradiation followed by composting with food waste using an active EAc inoculum.