Degradation and detoxification of formalin wastewater with aerated biological filters and wetland reactors

Formalin wastewater containing high concentrations of formaldehyde and TOC was treated and detoxified with biological aerated filter (BAF) and wetland reactors. At similar formaldehyde loading rates (about 0.01–0.9 kg/m3 d) both reactors provided high efficiencies but the BAF was more efficient at treating formaldehyde and TOC with average eliminations of 98 and 92%, respectively. However, the BAF effluent was not always detoxified according to the Lemna minor toxicity test as growth inhibition was above 20%. Although the elimination of formaldehyde and TOC achieved by the wetland reactors (81 and 25%, respectively) was lower than that of the BAF, they provided higher total nitrogen reduction. The combination of BAF and wetland reactors is proposed as a novel and convenient method for the treatment of formalin wastewater as it provided almost complete elimination of formaldehyde and detoxified samples with L. minor negative growth inhibition (−45 to −52%).