The mechanism of alkali to inhibit the organics polymerization in improving the biodegradability of wastewater treated by heat/peroxydisulfate

High-temperature wastewaters can themselves activate peroxydisulfate (PDS) to remove aromatic contaminants via polymerization. This, however, may result in an insufficient carbon source for denitrification during biochemical treatment, and the formed polymers, without a proper reuse method, will be costly to handle as hazardous waste. This study demonstrates that the addition of NaOH can suppress the polymerization of aromatic contaminants, which is observed not only in simulated wastewater but also in actual coking wastewater (ACW). Taking phenol as an example, the formation of phenoxy radical (PhO•) through the reaction between SO 4 •- and phenol is the crucial step for phenol polymerization. The addition of NaOH can convert sulfate radicals (SO 4 •– ) to hydroxyl radicals (HO•), and simultaneously, HO• can quickly consume PhO•. Both processes contribute to the inhibition of phenol polymerization. After treatment with heat/NaOH/PDS, the biodegradability of ACW is significantly enhanced with a relatively low carbon source loss (around 16%). Moreover, Fourier transform-ion cyclotron resonance mass spectrometry analysis indicates that the transformation of polyphenols to highly unsaturated and phenolic compounds is beneficial for the biodegradability improvement of ACW. Therefore, the NaOH/PDS system is an effective way to utilize waste heat and enhance the biodegradability of wastewater.