基于CaO调节的太阳能辅助加热猪粪沼液氨吹脱工艺研究

Ammonia stripping process via solar assisted heating for swine manure biogas slurry based on CaO regulation

氨吹脱工艺可在氨氮高效去除的同时实现氮素转化,是沼液养分回收的理想方案。在传统吹脱工艺中,碱剂添加,特别是NaOH和加热成本占总成本70%以上,导致运行成本较高。为降低猪粪沼液氨吹脱工艺能耗,该研究探讨使用低成本钙剂CaO替代NaOH调节沼液pH值,采用太阳能加热替代传统加热耦合氨吹脱工艺处理沼液。结果表明:CaO不仅能调节沼液pH值,还具有一定絮凝效果,且以石灰乳形态添加效果更好。当添加浓度为5 g/L时,沼液pH值不低于12.0,沼液浊度、COD、TP去除率分别为88.1%、50.1%、93.8%。不同吹脱组(氨氮去除率高于80%)运行成本结果表明,氨吹脱工艺在高pH值(12.0)驱动而不加热(25℃)时沼液处理成本最低,为2.46元/m3,与温度驱动相比,成本降低了52.1%~68.7%。而加热可进一步提升氨氮去除率,将太阳能加热与氨吹脱工艺耦合实现了氨氮去除率的显著提升,沼液经10%石灰乳形态CaO以添加浓度为5 g/L调节后,利用自制的太阳能辅助加热的氨吹脱装置在夏季可获得超过97.5%的氨氮去除率,即使在冬季氨氮去除率也超过86%。该研究结果可为太阳能耦合氨吹脱低成本氨氮去除工艺实际应用提供可行性依据。

Biogas slurry treatment has transformed from'pollutant removal'to'nutrient recovery'in the context of'sustainable development'and'circular economy'.The ammonia stripping process can be expected to efficiently remove the ammonia nitrogen for the nitrogen transformation and the nutrient recovery from the biogas slurry.The cost of alkali addition(especially sodium hydroxide(NaOH)and heating)can account for more than 70%of the total cost in the stripping process,leading to higher operation costs.Therefore,this study aims to reduce the energy consumption in the ammonia stripping of swine manure biogas slurry.The calcium oxide(CaO)was used instead of NaOH to adjust the pH value of biogas slurry,due to its lower price.Solar heating was used to treat the biogas slurry,instead of the traditional heating coupled ammonia stripping.The results showed that the CaO adjusted the pH value of biogas slurry,indicating a certain flocculation effect.A better performance was then obtained in the form of calcium hydroxide.Once the added concentration was 5 g/L,the pH value of the biogas slurry exceeded 12.0,where the removal rates of turbidity,COD,and TP reached 88.0%,50.1%,and 93.8%,respectively.The influencing factors were ranked in the descending order of pH,temperature,and gas-liquid ratio on the efficiency of ammonia stripping.In the swine biogas slurry with the low buffering capacity,the pH of the swine biogas slurry should be controlled above 10.8 for the stripping,in order to ensure≥70%ammonia nitrogen removal rate.Meanwhile,there was an increase in the temperature for the higher efficiency of ammonia stripping at the higher pH of the biogas slurry.Only when the pH and temperature of the biogas slurry were adjusted to the optimal ranges,the increasing gas-liquid ratio significantly promoted the ammonia stripping efficiency.The lowest running cost was achieved in the ammonia stripping process under the condition of a high pH value of 12.0 without heating(25℃)was about 2.46 Yuan/m3.Compared with the temperature-driven ammonia removal rate,the cost was reduced by 52.1%-68.7%among various stripping parameters(ammonia nitrogen removal rate>80%).However,the heating further improved the ammonia nitrogen removal rate.The coupling of solar energy and ammonia stripping significantly increased the ammonia nitrogen removal rate.The biogas slurry was adjusted by CaO in the form of 10%calcium hydroxide with an additive concentration of 5 g/L.After that,the biogas slurry and air temperature increased to 40.7-48.2℃and 43.6-61.5℃using solar collectors,respectively.The ammonia nitrogen removal rate of≥97.5%was obtained by the self-developed solar-assisted heating ammonia stripping device in summer.Even in winter,the average air and biogas slurry temperatures after heating reached 37.6 and 31.4℃,respectively.The removal rate of ammonia nitrogen reached more than 86%.This finding can provide a promising coupled solar application for the removal of low-cost ammonia nitrogen.