Aqueous Phase Ammonia Removal and Destruction System (APARDS)

In order to meet NASA potable water standards using biological processing, additional purification is needed. Elimination of ammonia species is a significant post-treatment step to achieve this goal. New technology, combining membrane transport and electro-oxidation of ammonia, was developed to solve this problem without the use of expendables. The Aqueous Phase Ammonia Removal and Destruction System (APARDS) Phase I Program rigorously demonstrated the feasibility of each sub-process, and an integrated system was developed that removed and destroyed ammonia from a simulated bioreactor effluent. Membranes and process conditions suitable for ammonia removal have been determined. An Ammonia Removal Module (ARM) was designed for the efficient transfer of ammonia to a secondary electro-oxidation stream where the ammonia was destroyed. The electrolysis cell's electrodes, operational voltage, and flow characteristics were optimized to rapidly destroy ammonia. The integrated system has demonstrated the continuous transfer and destruction of 20 mg/hr of ammonia from a solution containing 450 mg/L of sodium nitrite, 150 mg/L of ammonium sulfate, 193 mg/L of ammonium nitrate, 1330 mg/L of ammonium chloride, 20 mg/L of acetic acid, and 20 mg/L of ethanol. During continuous operation, 96.7% of the influent ammonia was eliminated. Reduction of ammonia below 100 μg/L was also demonstrated for an ammonium chloride solution containing 50 mg/L of ammonia. The projected size of an APARDS designed to treat the waste water from a crew of four containing 500 mg/L of ammonia flowing at 90 mL/min included 1.81 m² of membrane area and 1.032 m² of electrode area. The theory of operation, basis for selection of membranes and electro-oxidation cell materials, design of the ARM and destruction loop, determination of permeation conditions, and experimental results from each unit process and the integrated process are presented.