Tunning processes for organic matter removal from slaughterhouse wastewater treated by immediate one-step lime precipitation and atmospheric carbonation

Abstract

Adsorption using unmodified/modified commercial activated carbons and constructed wetlands (CW) planted with Vetiveria zizanioides were evaluated as tuning processes for lowering chemical oxygen demand (COD) from slaughterhouse wastewater pretreated by the integrated process of immediate one-step lime precipitation and atmospheric carbonation. Powdered and granular activated carbons (PAC and GAC), and PAC and GAC incorporated with iron oxide nanoparticles (PACMAG and GACMAG) were used. COD removal using different adsorbent separation methods (i.e., sedimentation, filtration, or magnetic separation) was also evaluated. The adsorption results indicated that the best adsorbent doses and contact times of the studied adsorbents were 70 g L−1 and 5 min for PAC and PACMAG, and 60 g L−1 and 60 min for GAC and GACMAG. Under optimized conditions, GAC (75.7 ± 1.0%) and GACMAG (73.5 ± 2.1%) were more efficient than PAC (59.7 ± 1.0%) and PACMAG (59.0 ± 0.0%) in removing COD. The incorporation of iron oxide nanoparticles in GAC and PAC did not affect the adsorption of COD. The Temkin model was the best isotherm model found for PAC and PACMAG, while for GAC and GACMAG was the BET model. Pseudo-order n kinetic model was the best kinetic model found for all the adsorbents tested. There were no significant differences in the removal of COD between filtration and magnetic separations. Phytoremediation results indicated that increased COD removal efficiency occurred when the applied COD mass load decreased or when the bed depth was increased. Maximum COD removals of around 89.9–95.0% were achieved. Vetiveria zizanioides showed no signs of toxicity throughout the trials.