Ferrate (FeO₄²⁻) is believed to have a dual role in water treatment, both as oxidant and coagulant. Few studies have considered the coagulation effect in detail, mainly because of the difficulty of separating the oxidation and coagulation effects. This paper summarises some preliminary results from laboratory-based experiments that are investigating the coagulation reaction dynamically via a PDA instrument, between ferrate and humic acid (HA) at different doses and pH values, and comparing the observations with the use of ferric chloride. The PDA output gives a comparative measure of the rate of floc growth and the magnitude of floc formation. The results of the tests show some significant differences in the pattern of behaviour between ferrate and ferric chloride. At pH 5 the chemical dose range (as Fe) corresponding to HA coagulation was much broader for ferrate than ferric chloride, and the optimal Fe dose was greater. Ferrate oxidation appears to increase the hydrophilic and electronegative nature of the HA leading to an extended region of charge neutralisation. A consequence of the ferrate oxidation is that the extent of HA removal was slightly lower ( approximately 5%) than with ferric chloride. At pH 7, in the sweep flocculation domain, ferrate achieved much greater floc formation than ferric chloride, but a substantially lower degree of HA removal.

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The aim of this research is to define promising green techniques and natural deep eutectic solvents (NADESs) for pectin extraction from dragon fruit (Hylocereus polyrhizus) peels with the aid of the Box‐Behnken design. Among all possible methods and solvents in this study, the highest pectin yield was recorded for microwave‐ultrasound‐assisted extraction (MUAE) using the solvent system of choline chloride–glucose–water (5:2:5). Under the optimized condition including liquid/solid ratio of 35.25 ml/g, water/NADES ratio of 3.37 ml/ml, microwave irradiation of 14.26 min at 240 W followed by sonication of 46.07 min, the pectin yield was 19.39%. The obtained product could be verified as high methoxyl pectin with the degree esterification of 50.77% and as a pseudoplastic substance with the flow behavior index of 0.14. As a result, a combination of MUAE and NADES on pectin extraction from dragon fruit peels can favor a higher yield with desirable quality. Novelty impact statement The system of choline chloride‐glucose‐water can be used as an eco‐friendly solvent for pectin extraction. The sequential employment of microwave and ultrasound could provide better efficiency than their individual techniques. The combination of screening and the Box‐Behnken design could help deal with a large number of process variables, resulting in milder operation conditions with desirable product quality.