Simultaneous recovery of nutrients and water from human urine by a novel thermally activated peroxydisulfate and membrane distillation integrated system

Membrane distillation (MD) has been applied to urine recovery with growing interest and demand for resource recovery from waste. However, MD application to urine is limited by obstacles, including the inability to recover nutrients and water simultaneously, low separation efficiency due to ammonia permeation, and membrane fouling. Herein, a novel system integrating thermally activated peroxydisulfate with MD (TAP-MD) was developed to overcome the above obstacles. The synergy effects were found between TAP pretreatment and MD process. With TAP pretreatment, membrane fouling was alleviated by organics degradation and mineral precipitation reduction, resulting in significant improvements in MD performance. Water flux of pretreated urine decreased from 25 L/m2/h to 15 L/m2/h after 80 % of water recovery, but that of unpretreated urine decreased to near zero after 38 % of water recovery. Meanwhile, MD process revealed further enhancement in urine stability by activating residual peroxydisulfate, reducing nutrient losses due to ammonia volatilization during storage and utilization of concentrated fertilizer. As a result, nearly 92.95 % of N-urea, 97.35 % of P, and 99.77 % of K was recovered as concentrated liquid fertilizer, meanwhile, 80 % of water was recovered as high-quality reclaimed water. The energy efficiency was improved by reusing waste heat from pretreatment. The TAP-MD system achieved a 45.63 % increase in thermal efficiency and a 38.25 % reduction in specific energy consumption compared to no pretreatment. This study developed an energy-efficient and high-performance separation treatment for complete resource recovery from urine.