Pretreatment of coking wastewater by acid out, micro-electrolysis process with in situ electrochemical peroxidation reaction

The coking wastewater was pretreated by acid out, micro-electrolysis process with in situ electrochemical peroxidation (ECP) (approximately 0.013–0.015 M H2O2) reaction to reduce the subsequent processing load. The results showed that the acidification process brought about changes not only in organic species of contaminants but also in decrease of COD, NH3N in wastewater through precipitation and some special reactions, resulting in 33% of COD and 9.7% of NH3N removal. Then Fe/C micro-electrolysis (ME) with in situ ECP reaction exhibited a stronger ability to remove the COD and NH3N than that with ex situ Fenton reaction, because at this stage, for the two reaction models, the total COD and NH3N removal were 65%, 26% and 43%, 25% in sequence, but in view of the contribution of only Fenton reaction to the whole COD and NH3N removal, they were 26%, 4.2% (the former was about six times as strong as the latter) and 9.3%, 8.1%, respectively. So it was reasonable to deduce that there was a prominent synergistic effect on COD removal between the dynamic Fe/C micro-electrolysis and the Fenton reaction; furthermore, the Fenton reaction in in situ ECP process was not only high-efficient but also low-cost. These advantages might mainly be attributed to the technique of dynamic Fe/C ME with in situ ECP reaction, as it was presumed that the technique might promote some favorable reactions involved, but inhibit those unfavorable ones. The major degradation mechanism of organic contaminants in effluent had been proposed.

► Acidification brought about precipitation and induced special chemical reactions.
► The COD removal was 65% in micro-electrolysis with in situ ECP.
► A synergistic effect between micro-electrolysis and Fenton reaction was revealed.