Performance of Aerobic Sludge Granulation in the Treatment of High-Strength <i>N</i>-Methyl-2-Pyrrolidone (NMP) Wastewater

NMP is a typical N-heterocyclic compound and has been widely used in several industries, such as the lithium battery industries. High-strength NMP wastewater was difficult to treat due to its strong toxicity to microorganisms. Since aerobic granular sludge (AGS) had a unique layered structure and exhibited high tolerance to organic loading rate (OLR), herein, AGS was directly cultivated with the influent NMP of 10,000 mg/L (OLR of ∼5.8 kg COD/(m3 d)) in a sequencing batch reactor with the inoculum of activated sludge. Granulation was successfully completed in 20 days with a D50 of 520 μm, SVI30 of 53.1 mL/g, and SVI30/SVI5 of 0.9. COD and TN removal ratio were maintained at >97.2% and 28.3%–46.5% during the long-term operation, in which genera Methylobacillus, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, and Arenimonas were the main bacteria. The relatively low TN removal was similar to other biological treatment processes, which was primarily due to the evident stepwise carbon removal and nitrogen release, as well as the suppression of nitrifying bacteria. Furthermore, an up-to-standard AGS-two-stage-A/O process was developed using Aspen Plus V10. To our knowledge; this study first developed the AGS system for high-strength NMP wastewater treatment, and it showed the highest NMP-stress tolerance in various NMP biodegradation strategies.