Synthesis, characterization and application of a bio-derived ZnO nano-powder from spinacia oleracea leaf extract for the removal of BOD and COD from tannery wastewater

Abstract

Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) as biological and chemical pollutants of wastewater are renowned environmental problems. A study of the performance of BOD and COD degradation via adsorption was undertaken using Bio-derived ZnO nanopowder (ZnO-NP), synthesized using leaf extract of Spinacia oleracea, and Zn (NO3)2 at 500 0C, following a simple and green approach. XRD, SEM, FTIR, EDS and BET analysis were used to characterize the nano-adsorbent. EDS spectrum recorded elemental weight compositions of 67.33% and 32.67% for Zn and O, while the FTIR absorption peaks revealed the presence of Zn-O–H and Zn-O. Surface area analysis revealed the mesoporous structure of the ZnO-NPs. The reduction efficiency of the ZnO-NPs was evaluated in the presence of raw tannery wastewater by application of treatment time and adsorbent dosage as parametric factors; results obtained were compared to environmental regulatory limits (WHO and NESREA). Contact times reported removal efficiencies of 81.5-90.8 % and 12.8-50 % for BOD and COD, while adsorbent dosage-influenced BOD and COD removal at an optimum contact time of 30 minutes was found to be 79.2 - 97.5 % and 27.8 to 55.6 % respectively. This study reveals that ZnO nanopowder is better applied as BOD reductants over COD for spent tan liquor.