Optimal Selection Of Pretreatment Methods Of Formaldehyde Wastewater

Due to the toxic effect to microbe, the formaldehyde wastewater is hard to be dealed with by the biochemical treatment. In the experiments of treating formaldehyde by extensive investigation and research, this paper studied the effective pretreatment and lowered the concentration of formaldehyde wastewater to the acceptable level of microbe by physical and chemical ways.First, based on the research of the air striping method and its characteristic, formaldehyde's initial concentration influence on the removal efficiency, temperature and gas amount influence on the process, this paper work out the striping curve. At room temperature, the striping process is similar to first order reaction kinetics, dC/dt = -0.0423C, t_1/2 = 16h. Air striping method adapts to high concentration formaldehyde wastewater and if the formaldehyde concentration is lower than 2000 mg/L, it will spend longer time and is not economical.Formaldehyde is a strong reducing agent, could be removed by oxidant. In the experiments of treating formaldehyde by pyrolusite catalytic, NaClO, NaClO₂, ClO₂, electrolysis and KMnO₄, this paper find that KMnO₄ do best in remove formaldehyde and the reaction speed is high. It can make the formaldehyde concentration lower from 741 mg/L to 150 mg/L within 20 minutes when the pH value is 11, the mol ration between HCHO and KMnO₄ is 1:0.9. The pH value behaves strong influence on the reaction. KMnO₄ is a kind of water treatment agent in common use and its price is moderate, so it could be considered to use in dealed with formaldehyde wastewater in engineering application.It is the first choice in pretreament of formaldehyde wastewater by lime (Ca(OH)₂) to catalyze the formaldehyde into carbohydrate. The method has the advantage of fast reaction, high formaldehyde removal and low costs. The rearch indicates that the temperature behaves strong influence on the reaction efficiency: when the initial formaldehyde concentration is 5000 mg/L, it spends 1.7h to remove 99.1% of formaldehyde at 50℃ and only 0.7h at 60℃.