Get started
Work

Study of total ammoniacal nitrogen recovery from wastewater using membrane-based processes: forward osmosis, reverse osmosis and nanofiltration

Year: 2025
Type: dissertation
Abstract: [eng] The recovery of nutrients from livestock manure, which are rich in macronutrients such as nitrogen, phosphorus, and potassium, offers a sustainable and environmentally friendly alternative to synthetic fertilizers. Membrane technologies, whether applied individually or as part of integrated treatment systems, have gained prominence due to their effectiveness in removing pollutants, recovering nutrients, and treating a wide variety of waste effluents. This thesis investigated the permeation behavior of ammonia derived from different ammonium salts using different membrane-based technologies: forward osmosis (FO), reverse osmosis (RO) and nanofiltration (NF). The study focused on the rejection of total ammoniacal nitrogen (TAN) in synthetic solutions with high concentrations of ammonium salts (NH₄Cl, (NH₄)₂SO₄, and NH₄HCO₃) formulated to simulate the nutrient composition of livestock manure. The aim was to evaluate the effects of the counter-anion of the salt, the pH of feed solution, and the type of membrane influence on TAN rejection and recovery efficiency. A commercial thin-film composite FO membrane was used to evaluate TAN rejection and recovery. The primary objective was to determine the permeability coefficients of both the ammonium ion and ammonia by fitting experimental data to a mathematical model. This model was based on the solution–diffusion mechanism, the Nernst–Planck equation, and film theory, incorporating ammonium-ammonia equilibrium (Ka). Before estimating the TAN permeability coefficients, key model parameters were first determined using sodium chloride and sodium sulfate as draw solutions and deionized water as the feed solution. The final results showed that the ammonia permeability coefficient (6.18 μm/s) was much higher than that of the ammonium ion (0.45 μm/s for NH₄Cl and 0.0136 μm/s (NH₄)₂SO₄), indicating the high diffusivity of ammonia as a small, uncharged molecule, through the membrane, and the effective rejection of ammonium ion due to its ionic nature and the membrane’s selectivity. Commercial thin-film composite RO membranes (SW30 and BW30) and NF membranes (MPF-36, NF90, Desal 5DK and MPF-34) were analyzed by determining the permeate flux and sodium chloride rejection. Particularly, the NF membranes were characterized by calculating their effective membrane pore radius and effective membrane thickness. These parameters were determined by fitting the experimental rejection of uncharged solutes to a mathematical model, which was based on the film-thin theory, steric partitioning equilibrium and the extended Nernst–Planck equation. The conventional procedure of using glucose, or alcohol-based molecules, for this analysis was found to be unsuitable for accurately determining these membrane characteristic parameters. Instead, this work proposed the use of glycine in its zwitterion specie, as it is a small molecule with a limiting rejection around 50% and is unable to interact with the polymeric matrix of the membrane. Among the NF membranes tested, NF90 showed the highest permeate flux and solute rejection, attributed to its low effective pore radius and membrane thickness. TAN rejection was also evaluated using RO and NF membranes under a fixed applied transmembrane pressure of 20 bar. At pH values below 7, TAN rejection was very high for all membranes due to size and Donnan exclusions. Among them, the SW30 membrane showed the highest rejection, reaching approximately 99.5% for (NH₄)₂SO₄. However, at pH higher than pKa of the ammonium-ammonia, TAN rejection decreased significantly reaching a minimum value of around 10% for the NF90 and MPF-34 membranes with NH₄Cl solutions at pH 11.5. TAN recovery was theoretically evaluated in a hybrid membrane system, combining NF membranes operated under alkaline conditions to promote TAN permeation with the SW30 membrane operated at pH 6.5 to retain TAN. Based on ammonia permeability and membrane properties, the NF90 membrane was operated at pH 9.5 and the MPF-34 membrane at pH 11.5. The NF90-SW30 system achieved a TAN recovery of 48.3%, with an overall chemical consumption cost of 0.586 €/kg of (NH₄)₂SO₄ produced. In comparison, the MPF-34-SW30 system yielded a higher TAN recovery of 64.8%, with an increase of 24.4% in the chemical consumption costs. Moreover, the elevated salinity of the retentate stream in the MPF-34-SW30 system suggests that the NF90-SW30 system yields a higher-quality liquid fertilizer at a lower chemical expense.
Author: Shahgodari, Shirin
Language: English
Open Access status: green
OpenAlex ID: W7115984684
Cites:
Cited by:
Related to: