Temperature Effects on Biotic and Abiotic Mechanisms of Nitrogen Removal Enhanced by Polybutylene Succinate in Synthetic Low-Carbon Wastewater

Using polybutylene succinate (PBS) to enhance nitrogen removal from low-carbon wastewater has gained increasing attention, yet its temperature adaptability remains unclear. PBS-enhanced nitrogen removal and its coupled bio-abiotic mechanisms were evaluated from 5 to 34 °C in a lab-scale system treating synthetic wastewater. High total nitrogen (TN) removal efficiency of 89.9% was achieved at 23–25 °C with influent TN of 60.8 mg/L, indicating an optimal temperature window. Mechanistic analysis revealed that temperatures above 23 °C promoted higher microbial community diversity, fostering a consortium dominated by unclassified_Burkholderiaceae (7.73–13.93%) and Leucobacter (6.29–7.47%), accompanied by enrichment of carbon/nitrogen metabolism-related genes and efficient nitrogen removal. Temperatures above 23 °C also maintained a high organic matter diffusion coefficient (0.043–0.222 Å2/ps), enabling microorganisms to fully utilize carbon sources. A random forest model linked the diffusion coefficient closely to pollutant removal efficiency and identified low-temperature-adapted genera (Flavobacterium, Dechloromonas) and functional genes (gapdh, fba, gpmI, napA, napB, nosZ), offering insights for enhancing low-temperature nitrogen removal. The model predicted effluent TN well (R2 > 0.98) and confirmed effluent NH4+-N as the dominant driver of TN variation. Pilot-scale tests with real wastewater are still needed. This study provides theoretical support for PBS-enhanced nitrogen removal in low-carbon wastewater.