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Abstract
Formaldehyde is a recalcitrant pollutant, which is difficult to remove from wastewater using conventional and advanced treatments. The objective of this research was to remove the organic matter from formaldehyde from an industrial wastewater, achieving its total mineralization and allowing the reuse of the water. The treatment was based on the reaction of formaldehyde with nitric acid, which was first studied and modelled with synthetic waters. Results show that it was possible to almost completely mineralize the formaldehyde (>95% TOC removal) at the best conditions studied (1.72 M of nitric acid and 85 °C of temperature). The addition of NaNO2 accelerated this reaction; however, after 2 h of reaction time, its effect was negligible at the maximum concentration of HNO3 studied. The results obtained with industrial wastewater fit well with the model. It is concluded that formaldehyde in actual wastewaters can be successfully removed through direct mineralization with nitric acid, under selected conditions.
Highlights
Formaldehyde is a recalcitrant organic compound widely used around the world due to its high reactivity, colorless nature, stability, purity in commercial form and low cost [1]
Mineralization was studied along the reaction time, regarding the HNO3 and NaNO2 concentrations at different temperatures (Figures 1 and 2)
The concentration of 0.17 M of HNO3 achieved a maximum of 20% TOC removal at the best conditions tested (2 h of reaction time, 85 or 100 ◦ C and 100 mM NaNO2 ; data not shown), and at the beginning of the reaction (15 min), remaining almost constant thereafter
Summary
Formaldehyde is a recalcitrant organic compound widely used around the world due to its high reactivity, colorless nature, stability, purity in commercial form and low cost [1]. It is used in many industrial products, including adhesives [2], paints [3], resins [4], textiles [5,6], wood-based panels [7], ethylene glycol [8] and other synthetic products in chemical and petrochemical plants [9], leading to concentrations of up to 10,000 mg/L in wastewater [10]. The state of the art shows the use of different advanced oxidation processes (AOPs) as pre-treatment for the removal of formaldehyde, such as photocatalysis, Fenton, photo-Fenton and electro-Fenton processes, ozonation with the addition of H2 O2 , catalytic ozonation and H2 O2 /UV process [14,15,16,17]
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