Enhanced denitrification using high-molecular-weight poly(lactic acid) blended with lactide as an effective carbon source

The utilization of wasted Poly(lactic acid) (PLA) as low-cost carbon sources in solid-phase denitrification is hindered by its low biodegradability, which can be attributed to its high molecular weight . This study presents a new approach by blending high-molecular-weight PLA with a small amount of ʟ-lactide (PLA/LA x ) to treat nitrate-contaminated wastewater. The addition of ʟ-lactide enhanced the release of carbon from high-molecular-weight PLA. An impressive denitrification efficiency of 96.7% was achieved, accompanied by extremely low levels of accumulated NO 2 - - N ${\text{NO}}_2^{-}-\text{N}$ (0.1 mg/L) and NH 4 + - N ${\text{NH}}_4^{+}-\text{N}$ (0.4 mg/L). The quantity of ʟ-lactide used significantly impacted the bacterial community structure. A high abundance of the phyla Bacteroidota and Chloroflexi associated with polymer degradation was observed. The most dominant denitrifier was the genus unclassified_f__Rhodocyclaceae belonged to the phylum Proteobacteria . This study demonstrates that blending PLA with just 5 wt% lactide can transform it into a highly effective solid-phase carbon source to eliminate nitrates.