Modified distillers' grain activated carbon for nitrogen and phosphorus removal from actual distillery wastewater: Performance and mechanism

Discharge of nitrogen and phosphorus‑rich distillery wastewater can damage aquatic ecosystems and cause serious environmental problems such as eutrophication. Conventional treatment methods are costly, energy-intensive, and generate secondary pollution. Granular activated carbon (GAC) is an efficient adsorbent, and modification can further improve its performance. Here, we prepared modified GAC from distiller's grains and systematically evaluated its adsorption performance and mechanisms for nitrogen and phosphorus removal from distillery wastewater. Results showed that NaOH modified GAC (NaOH-GAC) exhibited the highest removal for nitrogen and phosphorus, reaching 85.9% and 48.8%, respectively. This might be mainly because the specific surface area of NaOH-GAC reached 60.7 m2/g, and the surface was rich in functional groups such as hydroxyl and carboxyl groups. The adsorption process conformed to Langmuir monolayer adsorption isotherm (R2>0.911) and pseudo-second-order kinetic model (R2>0.995). The adsorption mechanism was mainly chemical adsorption, involving electrostatic interactions and surface complexation. In the actual distillery wastewater test, the removal of ammonia nitrogen and phosphate were 96.6% and 56.9%, respectively. These findings provide a practical, cost-effective, and eco-friendly treatment strategy that simultaneously achieves waste valorization and pollutant removal, offering a promising solution for nitrogen and phosphorus removal in the distillery industry.