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. 2024 Apr 29;14(5):102.
doi: 10.3390/membranes14050102.

Transmembrane Chemical Absorption Process for Recovering Ammonia as an Organic Fertilizer Using Citric Acid as the Trapping Solution

Ricardo Reyes Alva  1 , Marius Mohr  2 , Susanne Zibek  1   2
Affiliations

Transmembrane Chemical Absorption Process for Recovering Ammonia as an Organic Fertilizer Using Citric Acid as the Trapping Solution

Ricardo Reyes Alva et al. Membranes (Basel). .

Abstract

Membrane contactors are among the available technologies that allow a reduction in the amount of ammoniacal nitrogen released into the environment through a process called transmembrane chemical absorption (TMCA). This process can be operated with different substances acting as trapping solutions; however, strong inorganic acids have been studied the most. The purpose of this study was to demonstrate, at laboratory scale, the performance of citric acid as a capturing solution in TMCA processes for recovering ammonia as an organic fertilizer from anaerobic digestor reject water using membrane contactors in a liquid-liquid configuration and to compare it with the most studied solution, sulfuric acid. The experiments were carried out at 22 °C and 40 °C and with a feed water pH of 10 and 10.5. When the system was operated at pH 10, the rates of recovered ammonia from the feed solution obtained with citric acid were 10.7-16.5 percentage points (pp) lower compared to sulfuric acid, and at pH 10.5, the difference decreased to 5-10 pp. Under all tested conditions, the water vapor transport in the system was lower when using citric acid as the trapping solution, and at pH 10 and 40 °C, it was 5.7 times lower. When estimating the operational costs for scaling up the system, citric acid appears to be a better option than sulfuric acid as a trapping solution, but in both cases, the process was not profitable under the studied conditions.

Keywords: TMCA; TMCS; ammonia recovery; citric acid; hydrophobic membrane contactor; membrane stripping; reject water; supernatant; transmembrane chemical absorption.

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Conflict of interest statement

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

Figures

Figure 1
Figure 1
Ammonium/Ammonia equilibrium. Reprinted/adapted with permission from [16].
Figure 2
Figure 2
Closed-loop bench-scale setup (1) Hydrophobic membrane contactor; (2) Feed water tank; (3) Trapping solution tank; (4) Peristaltic pump; (5) Temperature controller; (6) NaOH container; (7) Dosing pump; (8) Bench scale; (9) Magnetic agitators; (10) pH sensor; (11) Temperature sensor; (12) Multimeter; (13) Barometer; (14) Air supply (for cleaning).
Figure 3
Figure 3
(a) NH3 removal efficiency in the TMCA process when using C6H8O7 vs. H2SO4 as the trapping solution (b) NH3 recovery efficiency comparison between citric and sulfuric acid in the TMCA process.
Figure 4
Figure 4
TMCA process efficiency comparison when using citric and sulfuric acids as trapping solutions (a) at pH 10 (b) at pH 10.5.
Figure 5
Figure 5
Water vapor transport in TMCA using C6H8O7 and H2SO4 as trapping solutions.
See this image and copyright information in PMC

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