The nonrecyclability of the sorbents used to capture Hg from flue gas causes a high operation cost and the potential risk of exposure to Hg. The installation of wet electrostatic precipitators (WESPs) in coal-fired plants makes possible the recovery of spent sorbents for recycling and the centralized control of Hg pollution. In this work, a HS-modified Fe-Ti spinel was developed as a recyclable magnetic sorbent to recover Hg from flue gas as a co-benefit of the WESP. Although the Fe-Ti spinel exhibited poor Hg capture activity in the temperature range of flue gas downstream of flue gas desulfurization, the HS-modified Fe-Ti spinel exhibited excellent Hg capture performance with an average adsorption rate of 1.92 μg g min at 60 °C and a capacity of 0.69 mg g (5% of the breakthrough threshold) due to the presence of S on its surface. The five cycles of Hg capture, Hg recovery, and sorbent regeneration demonstrated that the ability of the modified Fe-Ti spinel to capture Hg did not degrade remarkably. Meanwhile, the ultralow concentration of Hg in flue gas was increased to a high concentration of Hg, which facilitated the centralized control of Hg pollution.
Chloramines
applied to control membrane biofouling in potable reuse
trains pass through reverse osmosis membranes, such that downstream
ultraviolet (UV)/H2O2 advanced oxidation processes
(AOPs) are de facto UV/H2O2-chloramine AOPs. Current models for UV/chloramine AOPs, which use
inaccurate chloramine quantum yields and ignore the fate of •NH2, are unable to simultaneously predict the loss of
chloramines and contaminants, such as 1,4-dioxane. This study determined
quantum yields for NH2Cl (0.35) and NHCl2 (0.75).
Incorporating these quantum yields and the formation from •NH2 of the radical scavengers, •NO and
NO2
–, was important for simultaneously
modeling the loss of chloramines, H2O2, and
1,4-dioxane in the UV/H2O2-chloramine AOP. Although
the level of radical production was higher for the UV/H2O2-chloramine AOP than for the UV/H2O2 AOP, the UV/H2O2 AOP was at least 2-fold more
efficient with respect to 1,4-dioxane degradation, because chloramines
efficiently scavenged radicals. At low chloramine concentrations,
the UV/chloramine AOP efficiency increased with an increase in chloramine
concentration, as the level of radical production increased relative
to that of radical scavenging by the dissolved organic carbon in RO
permeate. However, the efficiency leveled out at higher chloramine
concentrations as radical scavenging by chloramines offset the increased
level of radical production. The level of 1,4-dioxane degradation
was ∼30–50% lower for the UV/chloramine AOP than for
the UV/H2O2-chloramine AOP when the concentration
of residual chloramines in RO permeate was ∼50 μM (3.3
mg/L as Cl2). Initial cost estimates indicate that the
UV/chloramine AOP using the residual chloramines in RO permeate could
be a cost-effective alternative to the current UV/H2O2-chloramine AOP in some cases, because the savings in reagent
costs offset the ∼30–50% reduction in 1,4-dioxane degradation
efficiency.
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