Mass Transfer and Selectivity of Ammonia Recovery Using Membrane Contactor during Manure Treatment
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    Abstract:

    Ammonia recovery from aerobic composting of livestock and poultry manure, or recovery from biogas slurry, can not only reduce pollutant and greenhouse gas emissions, but also obtain nitrogen fertilizer products. Aiming to use hollow fiber membrane absorption process for ammonia gas capture to solve the problems of large equipment volume and poor flexibility in the existing ammonia capture process, air stripping of diluted aqueous ammonia solution was used to prepare ammonia contained air. Then, the simulated ammonia contained air was flowed into hollow fiber membrane contactor, in which ammonia was captured by acid solution flowing in the tube side of the hollow fiber. By analyzing the total ammonium nitrogen concentration in the aqueous ammonia solution and acid solution, the ammonia mass transfer characteristics can be acquired. The results indicated that the mass transfer resistance of ammonia capture was mainly influenced by the gas phase mass transfer resistance and the membrane mass transfer resistance. The gas phase mass transfer resistance dominated at low air flow rates. However, when the air flow rate was increased to 5L/min, the gas phase mass transfer resistance was decreased by 53.6% compared with that of 0.5L/min, and the membrane mass transfer resistance dominants. The ammonia capture flux was increased with the elevation of ammonia concentration. Ammonia recovery ratio was above 95% at an air flow rate below 1L/min, while it was increased to above 99% at air flow rate of 0.5L/min. The ammonia recovery ratio was only related to the acid absorption capacity if sufficient ammonia retention time was provided. Under the dual influence of temperature and concentration differences, water vapor in the air would transfer into the membrane thus decreasing the product concentration. When the mass fraction of absorbent was 26%, the water transfer flux was 13.3 times higher than that of using 1% sulfuric acid solution. Besides, ammonia separation factor was decreased from 41.6 to 3.06. Acid concentration variation had no significant impact on the mass transfer of ammonia. Literature review showed that the ammonia release concentration in typical manure treatment was basically consistent with the concentration range. The hollow fiber membrane proposed had a wide applicability for capturing ammonia.

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History
  • Received:June 29,2023
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  • Online: February 10,2024
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