Adsorption of ammonia nitrogen in low temperature domestic wastewater by modification bentonite

Bentonite was used as adsorbent, which was modified by aluminum cross-linking and tannin double modification (Al-Tan-Bent), and the adsorbent has excellent removal performance for ammonia nitrogen (NH4+-N) from low temperature wastewater. In the experiments, the effects of adsorbent dosage, pH, contact time, and coexisting ions were analyzed in detail. The kinetic models were fitted by experimental data, and the results showed that the adsorption process of ammonia nitrogen fitted well with the pseudo-second order kinetic model. Langmuir adsorption isotherm has higher correlation coefficient (R2 = 0.9992), the saturated adsorption capacity was 5.85 mg/g at low temperature. Electrostatic adsorption is the main mechanism for removing ammonia (NH4+), and the whole reaction was spontaneous and exothermic. Different preparation conditions of adsorbent were also analyzed: tannin concentration, temperature, pH and reaction time. The best preparation conditions for ammonia nitrogen removal were: 2 g/L of the modified concentration, pH = 7.5, modification time at 1 h and room temperature (25 °C) respectively. The adsorbents were characterized by Scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface area and Zeta potential. The presence of tannin on bentonite and the effects of different modified pH were confirmed. The sedimentation of the sample was significantly improved.