In developing countries with increased industrialization, much research is carried out in order to recover the maximum ammonium from the environment. One of the methods to recover ammonium is Bipolar Membrane Electrodialysis (BPMED), a chemical-free technology that enables recovery and purification of the corresponding acid and base by the application of electrical energy. This thesis aims to evaluate five different BPMED cell configurations using the ammonium sulfate ((NH4)2SO4) salt. Experiments are based on evaluating operational parameters including flow rate, feed volume, base volume, and current density to achieve the maximum ammonium recovery using ammonium sulfate salt with efficient electrochemical energy consumption. Additionally, the optimum experiment was carried out with the best results of operational parameters to understand the overall impact on ammonium recovery and electrochemical energy consumption.

Removal of ammonium from simulated ammonium salt solutions was done using bipolar membrane electrodialysis (BPMED), without the use of chemicals. The effect of spacer thickness and open area on the overall energy consumption of BPMED to transport ammonium from the diluate was assessed in batch experiments. The electrochemical energy consumption decreased from 28 MJ/Kg-NH4+ to 16 MJ/Kg-NH4+ when the spacer thickness decreased from 750 μm to 140 μm.
The removal efficiencies of ammonium from the diluate increased from 77% to 85% when the spacer thickness decreased from 750 μm to 140 μm. These results show that with the increasing spacer thickness, the open area and porosity also increase, which accounts for higher resistance on the membrane stack. However, besides open area and porosity, it is the thickness of the spacer that plays a major role in higher energy consumption. This study demonstrated the energy-efficient application of BPMED for the removal of ammonium from simulated ammonium salt solutions.1

Excess nitrogen disposal into the environment increased with the discovery of an artificial way of nitrogen gas conversion to ammonia, and its implementation to industrial scale. The excess wasted fixed nitrogen ended up in rivers, lakes, oceans which resulted in degrading air, water and soil due to exceedance of the amount of nitrogen that can be absorbed by soil and plants. Currently, the global wastewater treatment objective has been adapting sustainable solutions by shifting from contaminant removal to resource recovery. Nutrients that were once considered as waste are now being considered as resources. Bipolar membrane electrodialysis (BPM-ED) in combination with stripper/scrubber is one of the combined technologies that aim at contaminant removal and resource recovery.

This study looks into energy efficiency and treatment performance from ammonium sulphate and ammonium citrate scrubber effluents by BPM-ED technology. A three-compartment BPM-ED was used to investigate the use of salt mixture in the feed solution and factors affecting ammonium yield.

Salt mixture of ammonium sulphate and tri-ammonium citrate were used. It was found that use of a salt mixture of ammonium sulphate and tri-ammonium citrate decreased the energy consumption and increased the current efficiency for both of the salts. Use of a mixture of ammonium sulphate and tri-ammonium citrate resulted in better energy performance than either of the salts when they were used alone. Ammonium recovery performance was higher when tri-ammonium citrate concentration was higher in the initial feed solution. This was due to increase in buffer capacity and basic pH in feed solution due to OH- leakages from base compartment. Sulphate ions were favored over citrate ions in their transfer through anion exchange membranes due to higher mobility of sulphate ions. As a further investigation a BPM-ED stack with different combinations, perhaps a two-compartment stack, can be tested to get a deeper understanding to optimize the operation.

Factors affecting ammonium yield that were investigated were H+ leakages and ammonia diffusion. It was found that H+ leakages were same for ammonium sulphate and potassium sulphate feed solutions and H+ leakages were not affected by ammonia diffusion. Ammonia diffusion resulted in higher energy consumption and loss of ammonium recovery potential. Ammonia diffusion increased even with experimental time of 60 minutes. Ammonia diffusion rates also increased through experimental time of 60 minutes. Ammonium and potassium transfer rates from diluate compartment did not follow a specific trend within the first 30 minutes. Clear reasoning behind this was unknown and the results were not completely satisfactory. In current study, it was assumed that ion cross-over and back diffusion were identical for ammonium and potassium. Investigating ion cross-over and back diffusion of the ions in BPM-ED could bring a deeper understanding to the energy efficiency and treatment performance.

The abundant presence of nitrogen in natural waters can be a threat to both humans and environment. Therefore, municipal and industrial wastewater streams need to be treated before their disposal in the environment. Currently used biological and physical-chemical treatment methods have drawbacks such as high greenhouse gas emissions, high energy use and high use of chemicals. This research used bipolar membrane electrodialysis (BPMED) as a technology for the removal of ammonium sulfate from industrial wastewaters with extreme characteristics. The industrial stripper/scrubber system removing nitrogen from industrial waters creates an ammonium sulfate rich water stream with a pH of 2, a temperature of 70 degrees Celsius and concentrations up to 250 g/L. The study investigated the influence of a low pH, high concentration and high temperature on the removal of ammonium and sulfate from wastewater and in situ generation of sulfuric acid and production of ammonium hydroxide. Key performance parameters to measure the influence of these extreme conditions were the efficiency of nitrogen removal in the form of ammonium current efficiency and ammonium removal efficiency}) and sulfate removal removal efficiency. Other key performance parameters of interest were the consumed energy for this removal in the form of electrochemical energy consumption, the purity of the generated acid and base and the final ammonium concentration in the base and the sulfate concentration in the acid. Model wastewater with a pH between 2 and 10, a concentration between 50 - 250 g/L ammonium sulfate and with a temperature between 20 degrees Celsius and 40 degrees Celsius was treated with BPMED. The influence of pH, concentration and temperature was researched independently in experiments of 180 minutes, after which the removal efficiency and the quality of the produced acid and base were assessed.