A two-stage sequential electro-Fenton (E-Fenton) oxidation followed by electrochemical chlorination (EC) was demonstrated to concomitantly treat high concentrations of organic carbon and ammonium nitrogen (NH-N) in real anaerobically digested food wastewater (ADFW). The anodic Fenton process caused the rapid mineralization of phenol as a model substrate through the production of hydroxyl radical as the main oxidant. The electrochemical oxidation of NH by a dimensionally stable anode (DSA) resulted in temporal concentration profiles of combined and free chlorine species that were analogous to those during the conventional breakpoint chlorination of NH. Together with the minimal production of nitrate, this confirmed that the conversion of NH to nitrogen gas was electrochemically achievable. The monitoring of treatment performance with varying key parameters (e.g., current density, HO feeding rate, pH, NaCl loading, and DSA type) led to the optimization of two component systems. The comparative evaluation of two sequentially combined systems (i.e., the E-Fenton-EC system versus the EC-E-Fenton system) using the mixture of phenol and NH under the predetermined optimal conditions suggested the superiority of the E-Fenton-EC system in terms of treatment efficiency and energy consumption. Finally, the sequential E-Fenton-EC process effectively mineralized organic carbon and decomposed NH-N in the real ADFW without external supply of NaCl.
This
study reports distillation-based salt removal by Ohmic heating
in a hybrid process, in which electrochemical oxidation (EO) and direct
contact membrane distillation (DCMD) are performed sequentially. In
addition to anodically destructing the organics, the hybrid process
also separated the sulfate-based electrolytes from treated water through
distillation, without consuming external energy, owing to the temperature
of the aqueous sulfate solution being elevated to 70 °C via resistive
heating. The hybrid process treated organic compounds in a nonselective
fashion, whereas DCMD alone did not completely reject (semi)volatile
organics. Integrating EO with DCMD made the hybrid process resistant
toward the wetting phenomenon; the process exhibited a steady distillate
flux and salt rejection as the initial loading of amphiphilic sodium
dodecyl sulfate was increased to 0.3 mM. Anodic persulfate formation
from the sulfate and Ohmic heating caused an in situ yield of the
sulfate radical in the feed solution; this eliminated membrane fouling,
according to the observation that the water flux, which was drastically
reduced upon adding alginate, was recovered immediately after an electric
current was applied. The hybrid process concurrently decomposed spiked
organics and removed naturally present inorganic ions in actual flue
gas desulfurization wastewater, without an external supply of electrolyte
and heat energy.
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