Advanced ammonia nitrogen removal and recovery technology using electrokinetic and stripping process towards a sustainable nitrogen cycle: A review

Ammonia removal and recovery from wastewater have been a critical issue worldwide and a key to achieve a sustainable nitrogen cycle and circular economy. Conventional ammonia removal via air stripping needs pH adjustment pretreatment with chemical additives while electrokinetic technologies can provide electrochemically in-situ pH control without chemicals needed. The integration of electrokinetic and air stripping technologies is a potential process for the simultaneous removal/recovery of ammonia/ammonium from wastewater. This study consolidates research findings of the separate research domains of electrokinetic and air stripping technologies and aims to identify an integrated process for the simultaneous nitrogen removal/recovery from waste streams. Process integration involves research on improved ammonia removal efficiencies and liquid side mass transfer performances using innovative air stripping system designs and gas-liquid contactors, e.g., rotating packed beds and membrane contactors, compared with the conventional stripping tower process. Findings in the applications and performances of electrokinetic separation processes, including electrodialysis, electrodeionization, capacitive deionization, electrochemical cell, and bio-electrochemical systems, on the removal/ recovery of ammonia/ammonium, are a crucial link to integration as well. Energy consumptions between 5-20.4 kWh/kg-NH4-N with a removal ratio of around 90% for electrokinetic processes are currently achievable, and some groups can be implemented on the biodegradable organic substrates from urine. Innovative hybrid technologies of ammonia nitrogen removal/recovery with energy production and co-product valorization that reduce the overall cost and energy consumption via integrated processes optimization, and discussions on the environmental impact assessment (via life cycle assessment) and economic benefit analysis (via techno-economic analysis) of ammonia recovery practices on waste streams are investigated.