Study Of Organic Wastewater Treatment Using Catalytic Ozonation

Ozone has been widely used for the treatments of organic wastewaters, however, the wastewater treatment processes using ozone still have a high operation cost and disadvantage of harmful by-product formations (such as formaldehyde and acetaldehyde). The aim of this study is to develop a new process to treat organic wastewaters using ozone and catalysts with a low operation cost and without harmful by-product formations.In order to treat the by-product, we at first investigated the ozonation of acetaldehyde, and then evaluated the effects of catalysts on acetaldehyde removal. Ozone was produced using non-thermal plasma discharges. Catalysts used in this were MnO₂ and activated carbon. As it was found that MnO₂ was more effective than activated carbon, we then used MnO₂ to accelerate acetaldehyde ozonation. The experiments were focused on the influence of discharge voltage, wastewater treatment time, initial acetaldehyde concentration, initial pH value of acetaldehyde solution, and MnO₂ amount on acetaldehyde removal.The main conclusions are as follows:1) Without catalysts, acetaldehyde could be oxidized to CO and CO₂ when ozone was introduced into the acetaldehyde solution. Acetaldehyde removal rate increased with increasing initial acetaldehyde concentration and initial pH value. The energy efficiency of acetaldehyde ozonation increased with the decrease in energy density. The maximum energy efficiency was 67.6 gCH₃CHO/kWh under conditions of O₂ flow rate 100 ml/min, discharge voltage 6.5 kV, initial acetaldehyde concentration 624 mg/L, initial pH value 12.0, and treatment time 175 min.2) With MnO₂, acetaldehyde was oxidized to CO and CO₂ when ozone was introduced into the acetaldehyde solution. Acetaldehyde removal rate increased with increasing MnO₂ amount, initial acetaldehyde concentration and initial pH value. The ozonation of acetaldehyde was the first order reaction of ozone. The energy efficiency of acetaldehyde ozonation also increased with the decrease in energy density. Under conditions of O₂ flow rate 100 ml/min, discharge voltage 6.5 kV, initial acetaldehyde concentration 624 mg/L, initial pH 12.0, and treatment time 175 min, the maximum energy efficiency was 271.6 gCH3CHO/kWh, 4 times as many as that without catalysts. The mechanism of acetaldehyde ozonation is given.