Applied Chemical Engineering

Engineering Application of Advanced Adsorbents in Urban Underground Sewage Treatment: Chemical Mechanisms of Pollutant Removal

Feng Song

Kyrgyz State Technical University named after I. Razzakov, Bishkek, 720044, Bishkek, the Kyrgyz, cdsogdang@163.com

Karimov Tashmukhamed

Kyrgyz State Technical University named after I. Razzakov, Bishkek, 720044, Bishkek, the Kyrgyz

DOI: https://doi.org/10.59429/ace.v9i1.5896

Keywords: adsorption; biochar; activated carbon; underground sewage; heavy metals; pharmaceuticals; pilot-scale; China

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Abstract

The sewage treatment systems in the cities demand small and efficient technologies that can eliminate both traditional and emerging pollutants. However, the practical use of the high-technology adsorbents in real-life situations of municipal wastewater is still limited. Engineering usage of high-performance adsorbents, such as the granular activated carbon (GAC), activated biochar, and Fe₃O₄-functionalized biochar composites, was examined in this work using actual municipal sewage samples of large metropolitan regions in China and pilot-scale treatment units. Experiments on batch adsorption, fixed-bed column studies and a 60-day pilot-scale experiment on adsorption were carried out to assess the adsorption performance, kinetics, equilibrium behavior, and regeneration potential.

Fe₃O₄- biochar composite demonstrated the best adsorption capacity to heavy metals and pharmaceuticals with an equilibrium adsorption capacity of 121.5mg g⁻¹ of Pb2+, 77.8mg g⁻¹ of Cd²⁺ and 132.6mg g⁻¹ of ciprofloxacin, whereas the GAC had a high adsorption capacity of methylene blue (210.3mg g⁻¹). The kinetic analysis showed that adsorption was correlated to pseudo-second-order models with correlation coefficients greater than 0.98, which is an indication of processes of chemisorption. The Langmuir isotherm models were best fitted to the Pb2+ adsorption process, with maximum adsorption capacity of 188.9mg g⁻¹ of Fe₃O₄- biochar. A thermodynamic was used to show that adsorption was spontaneous and endothermic with ΔG° of −12.4 to −18.7 kJ mol⁻¹ and ΔH° of 26.3 kJ mol⁻¹.

Experiments involving continuous flow column proved the breakthrough times of Fe 3 O 4 biochar to be 25.8 h, GAC 18.5 h and biochar 12.3 h. Pilot-scale operation had removal efficiencies of 86.2% chemical oxygen demand, 91.6% Pb²⁺, 83.3% Cd²⁺, 95.2% methylene blue, and 91.8% ciprofloxacin. The efficiencies of adsorbent regeneration were found to be over 77 % following five adsorption-desorption cycles.

The findings show that, functionalized biochar and activated carbon by metal-oxide is a potential adsorbent in small-scale underground sewage treatment systems, and the adsorption process is controlled by the electrostatic attraction, surface complexation, hydrogen bonding, and π–π interactions. The work gives mechanistic information and engineering parameters of adsorption units integration at the underground wastewater treatment plant in cities.

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