Microcontaminant removal by solar photo-Fenton at natural pH run with sequential and continuous iron additions

• Continuous and sequential iron dosage allowed micropollutants removal at natural pH.
• Bicarbonates were detrimental to the process efficiency when using iron additions.
• Iron addition mode affects reaction time and efficacy.
• Continuous addition allows a better distribution of iron in the photo-reactor.
• Acetamiprid, thiabendazole and imazalil degradation could be achieved in 15 min.

This paper deals with iron dosage used to remove micropollutants in short reaction times with solar photo-Fenton at natural pH. The impact of bicarbonates on the process operated with iron additions was also considered. Different sequential and continuous dosage modes were studied at pilot plant scale to remove a pollutant mixture formed by acetamiprid, thiabendazole and imazalil at a concentration of 100 μg/L each and with hydrogen peroxide excess. Both operating modes proved successful in rapid pollutant degradation. Nevertheless, iron distribution in the system, which is a consequence of the dosage mode, is critical to both efficiency and degradation time and it was different for each dosage mode. Specifically, the iron sequence of 20 × 4 (20 mg/L Fe added four times every mixing time) removed acetamiprid in 20 min, which is the least reactive pollutant. Meanwhile, iron added continuously as an exponentially decreasing function allowed the shortest reaction time – 15 min for removal below the limit of detection.

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