Chemical Pretreatment of Formaldehyde-Containing Effluents

Lime was found in this study to be an efficient reagent to lower the concentration of formaldehyde in highly concentrated effluents down to and below the limits suitable for biological treatment systems. The results show that the reactions leading to formaldehyde elimination can be divided in two steps. In the first step, the reaction is relatively slow. More than two-thirds of the original formaldehyde disappears in the second step in a period as short as one-third of the first step. Such trend is followed in a temperature range of up to 92 °C. Economical considerations suggest maintaining the conditions of the process around the ambient temperature with no heat requirement. It was noticed that the efficiencies of formaldehyde removal better than 99% could be achievable even around room temperature. However, these efficiencies would result in quite a shorter period of time if the temperature was raised. The mathematical representation for the rate of formaldehyde removal was found to appear with an exponential behavior. It will be seen that the rate of formaldehyde removal is strongly dependent on temperature. The present survey proves that the formaldehyde-containing effluents can be treated in a pretreatment step by lime to maintain the formaldehyde concentration in a range that is safe for biological treatment systems.