Trace Iron as single-electron shuttle for interdependent activation of peroxydisulfate and HSO3-/O2 enables accelerated generation of radicals.

The generation of reactive oxygen species generally requires initiators in various environmental remediation processes, which necessitates high dosage of activators and downstream treatment for eliminating the accumulation of deactivated catalysts. Herein, a coupled process was constructed using trace iron for simultaneously activating HSO3-/O2 system and peroxydisulfate (PDS) oxidation system, where the iron ions (2 mg/L) transferred single-electron from the former system to the latter due to the moderate redox potential (Fe3+/Fe2+, +0.77 V) between the potentials of SO3·-/HSO3- (+0.63 V) and PDS/SO4·- (+2.01 V). Hence, the phenol degradation quickly occurred at a first-order kinetic constant of k1=0.223 min-1 due to the accelerated generation of sulfate radical (SO4·-) and hydroxyl radical (·OH) in the process. The k1 value was almost 6-fold of that in the deoxygenated condition (0.040 min-1). Density function theory reveals that the single electron shuttle spatially separates the electron-donating activation of HSO3- and electron-accepting activation of PDS, while avoiding the "mutual-annihilation" of HSO3- and S2O82- via direct two-electron transfer. Finally, utilizing the in-situ generated electron-shuttle (dissolved iron from cast iron pipe), the HSO3-/PDS reagent could efficiently inactivate the chlorine-resistant pathogens and inhibits biofilm regrowth inside the distribution systems at regular intervals or infectious disease outbreak in a neighborhood.

Nitrogen and phosphorous recycling from human urine by household electrochemical fixed bed in sparsely populated regions.

Decentralized treatment of human urine in sparsely populated regions could avoid the problem of sewage collection in traditionally centralized treatment schemes and simultaneously utilize the recovered N/P fertilizer in-situ to nurture gardens. Herein, an integrated electrochemical fixed bed packed with divided magnesite and carbon zones was constructed for the pretreatment of human urine, followed by the recovery of 95.0% NH4+ and 85.8% PO43- via struvite precipitation and NH3 volatilization as well as the on-site employment of the produced struvite as fertilizer. In the process, the acid/base zones created by electrochemical water splitting dissolved the magnesite filler as the Mg2+ source of struvite, further creating an ideal pH environment for struvite precipitation and NH3 volatilization in the effluent. Without the need to control solution pH by chemical addition, the system can resist impacts from changes in water quality by adjustment of the current density and flow rate, indicating its great potential for automatic operation. Life cycle assessment indicated that the on-site employment of produced struvite avoids the long-distance fertilizer transportation required for fertilization, thus reducing carbon emission by a hundred million tons per year if the household facility is driven by clean electricity.