3 research outputs found
Life-Cycle Cost and Environmental Assessment of Decentralized Nitrogen Recovery Using Ion Exchange from Source-Separated Urine through Spatial Modeling
Nitrogen standards for discharge
of wastewater effluent into aquatic
bodies are becoming more stringent, requiring some treatment plants
to reduce effluent nitrogen concentrations. This study aimed to assess,
from a life-cycle perspective, an innovative decentralized approach
to nitrogen recovery: ion exchange of source-separated urine. We modeled
an approach in which nitrogen from urine at individual buildings is
sorbed onto resins, then transported by truck to regeneration and
fertilizer production facilities. To provide insight into impacts
from transportation, we enhanced the traditional economic and environmental
assessment approach by combining spatial analysis, system-scale evaluation,
and detailed last-mile logistics modeling using the city of San Francisco
as an illustrative case study. The major contributor to energy intensity
and greenhouse gas (GHG) emissions was the production of sulfuric
acid to regenerate resins, rather than transportation. Energy and
GHG emissions were not significantly sensitive to the number of regeneration
facilities. Cost, however, increased with decentralization as rental
costs per unit area are higher for smaller areas. The metrics assessed
(unit energy, GHG emissions, and cost) were not significantly influenced
by facility location in this high-density urban area. We determined
that this decentralized approach has lower cost, unit energy, and
GHG emissions than centralized nitrogen management via nitrification-denitrification
if fertilizer production offsets are taken into account
Understanding the Catalytic Active Sites of Crystalline CoSb<sub><i>x</i></sub>O<sub><i>y</i></sub> for Electrochemical Chlorine Evolution
The chlorine evolution reaction (CER) is a key reaction
in electrochemical
oxidation (EO) of water treatment. Conventional anodes based on platinum
group metals can be prohibitively expensive, which hinders further
application of EO systems. Crystalline cobalt antimonate (CoSbxOy) was recently
identified as a promising alternative to conventional anodes due to
its high catalytic activity and stability in acidic media. However,
its catalytic sites and reaction mechanism have not yet been elucidated.
This study sheds light on the catalytically active sites in crystalline
CoSbxOy anodes
by using scanning electrochemical microscopy to compare the CER catalytic
activities of a series of anode samples with different bulk Sb/Co
ratios (from 1.43 to 2.80). The results showed that Sb sites served
as more active catalytic sites than the Co sites. The varied Sb/Co
ratios were also linked with slightly different electronic states
of each element, leading to different CER selectivities in 30 mM chloride
solutions under 10 mA cm–2 current density. The
high activity of Sb sites toward the CER highlighted the significance
of the electronic polarization that changed the oxidation states of
Co and Sb
Cation Incorporation into Copper Oxide Lattice at Highly Oxidizing Potentials
Electrolyte cations can have significant effects on the
kinetics
and selectivity of electrocatalytic reactions. We show an atypical
mechanism through which electrolyte cations can impact electrocatalyst
performancedirect incorporation of the cation into the oxide
electrocatalyst lattice. We investigate the transformations of copper
electrodes in alkaline electrochemistry through operando X-ray absorption
spectroscopy in KOH and BaÂ(OH)2 electrolytes. In KOH electrolytes,
both the near-edge structure and extended fine-structure agree with
previous studies; however, the X-ray absorption spectra vary greatly
in BaÂ(OH)2 electrolytes. Through a combination of electronic
structure modeling, near-edge simulation, and postreaction characterization,
we propose that Ba2+ cations are directly incorporated
into the lattice and form an ordered BaCuO2 phase at potentials
more oxidizing than 200 mV vs the normal hydrogen electrode (NHE).
BaCuO2 formation is followed by further oxidation to a
bulk Cu3+-like BaxCuyOz phase at 900 mV vs
NHE. Additionally, during reduction in BaÂ(OH)2 electrolyte,
we find both Cu–O bonds and Cu–Ba scattering persist
at potentials as low as −400 mV vs NHE. To our knowledge, this
is the first evidence for direct oxidative incorporation of an electrolyte
cation into the bulk lattice to form a mixed oxide electrode. The
oxidative incorporation of electrolyte cations to form mixed oxides
could open a new route for the in situ formation of active and selective
oxidation electrocatalysts