Acclimatization of a sequencing batch vertical oxidation pond with simulated agricultural wastewater using duckweed as vegetation: analysis of efficiency, Biomass, and Soil properties

Vertical oxidation pond operated in sequencing batch mode (HRT: 1.25 day) with duckweed as the vegetation was used to acclimatize with simulated agricultural wastewater. The maximum removal rate of urea [371 g/(m³.d)] and COD [222.4 g/(m³.d)] were observed at moderate concentrations of urea (500 mg/L), N-P-K (60 mg/L), and pesticide (20 mg/L). Inhibition and toxicity posed by higher concentrations, decreased the removals of urea (83% to 61%), COD (81% to 51%), and TDS (76% to 50%) at the end of the acclimatization. Steady removal (> 99%) of PO₄³⁻-P was observed during acclimatization. Effluent pH increased due to the generation of NH₄⁺-N (maximum 370 ± 5 mg/L) from the assimilation of urea. Oxidation of ammonia led to the maximum generation of NO₂⁻-N and NO₃⁻-N of 10 mg/L and 9 mg/L, respectively. Particles less than 300 μm increased, and both specific gravity (from 2.62 to 2.42) and maximum dry density (from 1.73 to 1.30 g/cm³) of the base soil decreased with an increase in urea, N-P-K, and pesticide. Reactor biomass increased (1.42 to 1.90 g/L) up to initial concentrations of urea (500 mg/L), N-P-K (60 mg/L), and pesticide (20 mg/L), then decreased (1.68 g/L) with an increase in concentration.