Sustainable ammonia recovery from low strength wastewater by the integrated ion exchange and bipolar membrane electrodialysis with membrane contactor system

Abstract

An energy-efficient and reagent-free system consisting of ion exchange, bipolar membrane electrodialysis and membrane contactor (IE-BMED-MC) was developed for recovering ammonia from low NH4+-N strength wastewater. In this system, NH4+ in the wastewater was firstly removed by ion exchange and then enriched in the acidic regenerant produced by bipolar membrane electrodialysis cell, eventually purified and recovered in membrane contactor without the addition of acid and base. A removal efficiency of over 97 % and recovery efficiency of 9 %-74 % with the energy consumption of 8.12–11.9 kWh·kg−1-N were achieved at current density of 0.5–2.5 mA·cm−2, and the nitrogen flux across the cation exchange membrane (174 g-N·m−2·d-1) was much higher than other ammonia recovery processes with low NH4+-N strength wastewater (<50 g-N·m−2·d-1) owing to the resin enrichment effect. Over six cycles, NH4+-N removal efficiency remained at about 90 % with energy consumption as low as 6 kWh·kg−1-N, where the spent regenerant was utilized as the base stream for next cycle to avoid discharge. Generally, this system realized high-efficiency ammonia recovery from low strength wastewater without chemical input and the cost of $0.425 per kg-N was lower than Haber-Bosch process.