Microwave-assisted decolorization and decomposition of methylene blue with persulfate

• Microwave with persulfate is an effective technique to degrade methylene blue (MB).
• The MB removal rate increases with final temperature (T) and [perfulfate].
• The T affects both decolorization and total organic carbon (TOC) removal of MB.
• The [perfulfate] affects only decolorization of MB significantly.
• The removal of TOC reaches 100% at higher T and [perfulfate] than decolorization.

This work experimentally determined the effect of a combination of microwave irradiation (MWI) and sodium persulfate (Na2S2O8, SPS) on decolorization and decomposition of methylene blue (C16H18N3SCl, MB). The effects of treatment temperature (70–100 °C, T) and SPS concentration (1–5 g l−1) at 8-min MWI time were characterized. The conversion rate of MB (50 mg l−1) was increased and accelerated by MWI, reaching 99.9% after heating for 8 min at 90 °C and 600-W MW power in the presence of 5 g l−1 of SPS; this is higher than the conversion rate (98.3%) of treatment by conventional heating for 30 min. The MB decolorization increased with T (p = 0.002) and initial SPS (p = 0.006). The total organic carbon (TOC) removal also increased with T (p = 0.004). Within the design boundaries, full decolorization was achieved at T ≥ 93 °C and SPS ≥3.5 g l−1. The TOC removal level reached 100% at T ≥ 95 °C and SPS = 5 g l−1. The results show that MWI combined with SPS is effective in decolorization and degradation of MB due to advantages of fast and effective processing.