This is the first report on the environmental occurrence of a chlorinated polyfluorinated ether sulfonate (locally called F-53B, C8ClF16O4SK). It has been widely applied as a mist suppressant by the chrome plating industry in China for decades but has evaded the attention of environmental research and regulation. In this study, F-53B was found in high concentrations (43-78 and 65-112 μg/L for the effluent and influent, respectively) in wastewater from the chrome plating industry in the city of Wenzhou, China. F-53B was not successfully removed by the wastewater treatments in place. Consequently, it was detected in surface water that receives the treated wastewater at similar levels to PFOS (ca. 10-50 ng/L) and the concentration decreased with the increasing distance from the wastewater discharge point along the river. Initial data presented here suggest that F-53B is moderately toxic (Zebrafish LC50-96 h 15.5 mg/L) and is as resistant to degradation as PFOS. While current usage is limited to the chrome plating industry, the increasing demand for PFOS alternatives in other sectors may result in expanded usage. Collectively, the results of this work call for future assessments on the effects of this overlooked contaminant and its presence and fate in the environment.
Electrochemical
systems are an attractive option for onsite latrine
wastewater treatment due to their high efficiency and small footprint.
While concerns remain over formation of toxic byproducts during treatment,
rigorous studies examining byproduct formation are lacking. Experiments
treating authentic latrine wastewater over variable treatment times,
current densities, chloride concentrations, and anode materials were
conducted to characterize byproducts and identify conditions that
minimize their formation. Production of inorganic byproducts (chlorate
and perchlorate) and indicator organic byproducts (haloacetic acids
and trihalomethanes) during electrolysis dramatically exceeded recommendations
for drinking water after one treatment cycle (∼10–30 000
times), raising concerns for contamination of downstream water supplies.
Stopping the reaction after ammonium was removed (i.e., the chlorination
breakpoint) was a promising method to minimize byproduct formation
without compromising disinfection and nutrient removal. Though treatment
was accelerated at increased chloride concentrations and current densities,
byproduct concentrations remained similar near the breakpoint. On
TiO2/IrO2 anodes, haloacetic acids (up to ∼50
μM) and chlorate (up to ∼2 μM) were of most concern.
Although boron-doped diamond anodes mineralized haloacetic acids after
formation, high production rates of chlorate and perchlorate (up to
∼4 and 25 μM) made them inferior to TiO2/IrO2 anodes in terms of toxic byproduct formation. Organic byproduct
formation was similar during chemical chlorination and electrolysis
of wastewater, suggesting that organic byproducts are formed by similar
pathways in both cases (i.e., reactions with chloramines and free
chlorine).
Efficient, inexpensive, and stable
electrode materials are key
components of commercially viable electrochemical wastewater treatment
system. In this study, blue-black TiO2 nanotube array (BNTA)
electrodes are prepared by electrochemical self-doping. The 1-D structure,
donor state density, and Fermi energy level position are critical
for maintaining the semimetallic functionality of the BNTA. The structural
strength of the BNTA is enhanced by surface crack minimization, reinforcement
of the BNTA-Ti metal interface, and stabilized by a protective overcoating
with nanoparticulate TiO2 (Ti/EBNTA). Ti/EBNTA electrodes
are employed as both anodes and cathodes with polarity switching at
a set frequency. Oxidants are generated at the anode, while the doping
levels are regenerated along with byproduct reduction at the cathode.
The estimated maximum electrode lifetime is 16 895 h. Ti/EBNTA
has comparable hydroxyl radical production activity (6.6 × 10–14 M) with boron-doped diamond (BDD, 7.4 × 10–14 M) electrodes. The chlorine production rate follows
a trend with respective to electrode type of Ti/EBNTA > BDD >
IrO2. Ti/EBNTA electrodes operated in a bipolar mode have
a minimum
energy consumption of 62 kWh/kg COD, reduced foam formation due to
less gas bubble production, minimum scale formation, and lower chlorate
production levels (6 mM vs 18 mM for BDD) during electrolytic wastewater
treatment.
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