Publication Details
Abstract
The treatment of petrochemical wastewater to modern discharge standards requires the complete removal of nitrogen compounds, which is achievable only through a single-stage nitri-denitrification process combined with a tertiary (polishing) stage. This paper presents the technological scheme, the kinetic-based design, and the techno-economic assessment of the biological and tertiary treatment facilities of the Sho‘rtan Gas-Chemical Complex (SGCC). The specific reaction-rate constants of nitrification, denitrification, oil-product oxidation and organic-matter oxidation were determined experimentally for the local wastewater and activated sludge using the contact method and Lineweaver-Burk linearization of the Michaelis-Menten model (R² > 0.98). Nitrification proved to be the rate-limiting process (V_max = 2.17 mg/(g·h); K_m = 0.85 mg/l), being the most sensitive to inhibition by phenols (IC₅₀ ≈ 5.3 mg/l) and salinity. A pre-denitrification (modified Ludzack-Ettinger) aerotank was designed: anoxic zone 220 m³, aerobic zone 515 m³, deaerator 32 m³ (total 765 m³), with an internal recirculation ratio R = 2.7 and a specific air demand of 825 m³/h. A sorption polishing filter (AG-3 activated carbon) reduces residual phenols below 0.04 mg/l. The combined scheme provides removal efficiencies of 95 % (BOD), 97 % (ammonium nitrogen) and 75 % (total nitrogen), and reduces the specific treatment cost by 22 % (from 3800 to 2970 UZS/m³) with a payback period of 2.87 years.