Peptide-modified nanocellulose from dairy waste for organic compound removal in dairy wastewater

Dairy effluent with a high organic loading demands efficient and sustainable treatment solutions. This work aimed to produce a peptide-modified crystalline nanocellulose (PCN C ) bio-adsorbent from dairy sludge and crustacean waste to remove organic compounds from industrial dairy wastewater. To optimize operational variables for maximum removal of chemical oxygen demand (COD), 5-day biochemical oxygen demand (BOD₅) and total organic carbon (TOC), response surface methodology (RSM) was applied based on a central composite design (CCD). Operational variables were pH (3–10), adsorbent dosage (100–500 mg L⁻1), contact time (15–55 min), peptide-to-cellulose mass ratio (0.5:1–3:1) and temperature (15–55 °C). The effective functionalization of the peptide and formation of a mesoporous structure with good thermal stability were validated by characterization using FESEM, XRD, FTIR, BET and TGA/DTG. Under the optimal conditions (pH 6.5, PCN C dose of 300 mg L⁻1, contact time of 35 min, peptide-to-cellulose mass ratio of 3:1 and temperature of 25 °C), the maximum removal efficiencies were 97.80%, 93.60% and 96.40% for COD, BOD₅ and TOC, respectively. The most significant factors were pH and PCN C dose according to analysis of variance (ANOVA) ( p < 0.0001). The quadratic models showed high predictive ability (R2 = 0.9519) and were experimentally validated with a relative error of < 0.50%. Furthermore, PCN C showed good reusability, with removal efficiencies of nearly 95% for COD, 92% for BOD₅ and 89% for TOC after five successive adsorption–desorption cycles. Generally, our results highlight the potential of PCN C as a bio-based adsorbent for dairy wastewater treatment while promoting waste valorization and circular economy concepts.