- Learn why in the commercial manufacture of resins it is a good practice to utilize sodium sulphite in wastewater treatment to convert formaldehyde to an easily biodegradable substance.
Many industrial activities utilise formaldehyde as a key chemical in organic synthesis including: synthesis of special chemicals such as pentaerythritol and ethylene glycol, synthetic resins, paper products, medicinal products and drugs and others, too numerous to mention. Therefore, effluents arising from these applications may contain significant amounts of formaldehyde. In a biodegradation experiments of a wastewater sample containing formaldehyde ranging from 31.5 to 125 mg/l, residual formalin (a solution of formaldehyde gas in water) ranging from 40% to 85%, respectively, was found at the end of the run (16 d) showing the inhibition effect of formalin which increased with the increase in formalin concentration. The biodegradation of formalin decreased significantly at concentrations higher than 300 mg/l. A method to convert formaldehyde to an easily biodegradable substance is herein described.
In the commercial manufacture of resins from phenol and formalin the reaction is never completely quantitative. As a result during the dehydration stage phenol and formalin are distilled from the wastewater. Phenol is toxic to several biochemical reactions. However, biological transformation of phenol to a non-toxic entity is possible through specialized microbes. Transformation of phenol is inhibited by the presence of formaldehyde. Biotransformation of phenol in a wastewater containing high concentrations of formaldehyde started shortly after treating the wastewater with calculated amounts of sodium sulphite. Sodium sulphite is believed to react with formaldehyde forming sodium formaldehyde bisulphite, which is not only non-toxic to microorganisms but also a biodegradable substance. From the DO measurements before and after the addition of sodium sulphite, the authors noticed that the dissolved oxygen in a wastewater containing formaldehyde is not affected by the addition of the calculated amount of sodium sulphite, which is just enough to consume the measured amount of formaldehyde in that wastewater.