Impacts of co-existing cations and suspended solids on ammonia recovery In membrane contactors
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School of Engineering |
Master's thesis
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en
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97
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Abstract
Resource recovery is increasingly receiving attention in wastewater treatment plants (WWTPs) as a transitioning step towards circular economy. Anaerobic digestion processes generate digestate, which after dewatering, produces reject water containing high ammonium concentrations along with co-existing ions and suspended solids. This study evaluates, for the first time, the individual impacts of cations (Na+, K+, Ca2+ and Mg2+) and suspended solids (SS) (glass beads, zeolite, kaolin, and cellulose) on ammonia recovery using hydrophobic gas-permeable PTFE membrane contactor. It also aims to address the operational performance of the contactor under high concentrations of ions and SS and its possible integration with bio-electrochemical system (BES). Four different concentrations from low to very high were tested, along with a synthetic ionic mixture (recipe) simulating reject water. A series of laboratory experiments were conducted to analyse ammonium concentrations in feed and acid solutions to evaluate and compare ammonia recovery efficiencies. An average of 61% ammonia recovery efficiencies was achieved with the control experiment containing 4500 mg NH4+/L. Most tested ions and suspended solids showed no significant deviation from the control, except for the recipe mixture, K+ (10 g/L), Ca2+( 3 g/L), Kaolin (5 g/L), and Cellulose (1 g/L), which showed minor variations. Mass balance calculations demonstrated possible leakages of ammonia from system imperfections; however, they remained within the acceptable range of ±30%. Although the study provided insightful results into performance of membrane contactors in elevated suspended solid and ionic concentrations, possible impacts of the ions and SS could not be reliably interpreted due to insufficient repetitions, short experimental duration, ammonia loss during transfer and other limitations such as equipment malfunctions and insufficient mixing. Overall, the results suggest that the mem-brane contactors can operate well under tested high concentrations of SS and ions and can be promising for integration with BES, which can be further validated with future studies. These can involve at least three replicates for longer duration, consistent experimental durations, finer SS, and real reject water to improve reliability and understand better the robustness of the membrane contactor system.Description
Supervisor
Haimi, HenriThesis advisor
Larsson, TimoKaljunen, Juho Uzkurt