A new particle material (CTS/ZMS) for removing ammonia and nitrate from groundwater: performance and regeneration

A new type of particle material modified zeolite molecular sieve (CTS/ZMS) is developed for the simultaneous removal of NH₄⁺-N and NO₃^--N in groundwater. To ascertain the optimal performance of CTS/ZMS, a custom central composite design (CCD) was utilised to assess the operational parameters (dosage and contact time) of CTS/ZMS composites. Batch experiments were carried out to determine the removal efficiency and adsorption capacity across varying pH values (3-12) and temperatures (5 °C to 30 °C). The results of response surface three-dimensional analysis showed the removal efficiencies of nitrate and ammonium ions are the highest at a dosage of 5.5 g/L of CTS/ZMS adsorbents and adsorption time of 6.25 h and are respectively observed to be 40%, and 80.2%. Adsorption thermodynamic analysis (ΔG<0, ΔH>0, ΔS⁰>0) revealed ammonia and nitrate adsorption on CTS/ZMS composites are spontaneous and feasible at high temperatures. SEM, EDS, BET, FTIR and XPS were employed for analyzing the adsorption mechanism of CTS/ZMS for NH₄⁺-N and NO₃^--N and included mostly ion exchange, electrostatic interaction, and hydrogen bonding. Different regeneration methods including water regeneration, thermal regeneration, and chemical regeneration for CTS/ZMS composites were analyzed to evaluate the removal efficiency of NH₄⁺-N and NO₃^--N. The saturated CTS/ZMS composites regenerated by first 1 mol/L NaCl solution, followed by 1 mol/L Na₂CO₃ solution demonstrated the highest ammonia and nitrate removal efficiency. The experimental data indicated pseudo-second-order kinetic model and the Freundlich model explained well the ammonia and nitrate adsorption process of regenerated CTS/ZMS composites. According to the Langmuir model, the regenerated CTS/ZMS can adsorb a maximum of 0.92 mg/g of ammonia and 1.98 mg/g of nitrate. The results demonstrate that CTS/ZMS composites serve as a potentially efficient adsorbent for removing ammonia and ions from groundwater. This study offers technical guidelines and support for the future production and application of CTS/ZMS.