Study on the adsorption of nitrogen and phosphorus from biogas slurry by NaCl-modified zeolite

A NaCl-modified zeolite was used to simultaneously remove nitrogen and phosphate from biogas slurry. The effect of pH, contact time and dosage of absorbants on the removal efficiency of nitrogen and phosphate were studied. The results showed that the highest removal efficiency of NH4+-N (92.13%) and PO43−-P (90.3%) were achieved at pH 8. While the zeolite doses ranged from 0.5 to 5 g/100 ml, NH4+-N and PO43−-P removal efficiencies ranged from 5.19% to 94.94% and 72.16% to 91.63% respectively. The adsorption isotherms of N and P removal with NaCl-modified zeolite were well described by Langmuir models, suggesting the homogeneous sorption mechanisms. While through intra-particle diffusion model to analyze the influence of contact time, it showed that the adsorption process of NH4+-N and PO43−-P followed the second step of intra-particle diffusion model. The surface diffusion adsorption step was very fast which was finished in a short time.本研究采用氯化钠改性沸石（NaCl-modified zeolite），用于从沼液中同步脱除氮与磷。考察了pH值、接触时间及吸附剂投加量对氮、磷脱除效率的影响。结果显示，当pH为8时，氨氮（NH4+-N）与正磷酸盐磷（PO43−-P）的脱除效率达到最高，分别为92.13%和90.3%。当沸石投加量处于0.5~5 g/100 mL区间时，氨氮与正磷酸盐磷的脱除效率分别为5.19%~94.94%与72.16%~91.63%。氯化钠改性沸石脱除氮、磷的吸附等温线可通过朗缪尔（Langmuir）模型良好拟合，表明该吸附过程遵循均相吸附机制。通过颗粒内扩散模型分析接触时间的影响后发现，氨氮与正磷酸盐磷的吸附过程符合颗粒内扩散模型的第二步动力学过程，其表面扩散吸附步骤速率极快，可在短时间内完成。