Study On Acetaldehyde Wastewater Alkaline Decomposition And Biological Methanogenesis

Large quantities of high-concentration toxic organic wastewater are produced during catalyzed oxidation process of ethene for acetaldehyde production. The organics in wastewater are difficult to remove by direct biological treatment, so the pretreatment technology for wastewater detoxification was required to develop. In this study, the organic pollutants composition and biological toxicity of the acetaldehyde wastewater were analyzed, then detoxification pretreatment technologies were compared and process parameters were optimized. Main conclusions are as follows.Acetic acid, aldehydes, chlorinated organic are the main specific pollutants in acetaldehyde wastewater. The wastewater showed significant toxicity against both anaerobic methane-producing sludge and aerobic activated sludge.Expanded granular sludge bed(EGSB) reactor was used to treat synthetic wastewater containing acetaldehyde wastewater. When acetaldehyde wastewater dosing concentrations was above 300mg/LCODCr, the activity of anaerobic sludge was inhibited with substantial declines of CODCr removal rate and methane production rate.Several detoxification pretreatment technologies was compared. It was indicated that the toxicity of wastewater could be reduced significantly by alkaline decomposition pretreatment. Reaction time, reaction temperature and alkaline dosage are important factors for the pretreatment. For the reduction of toxicity on aerobic activated sludge, inhibition of oxygen utilization rate(OUR) declined significantly after the pretreatment of reaction time of 0.5h, alkaline dosage of 1.2g/L, reaction temperature of 30℃. For the reduction of toxicity on anaerobic methane-producing sludge, inhition of methane-producing rate declined significantly after the pretreatment of reaction time above 3h, reaction temperature of 60 ℃,alkaline dosage above 2g/L. Most of the aldehydes and chlorinated organics in acetaldehyde wastewater were easy to decompose under alkaline conditions. However, a small number of chlorobated organics and aldehydes with high toxicity on anaerobic methane-producing sludge degraded slowly under alkaline conditions.Acetaldehyde wastewater after alkaline decomposition pretreatment was treated with anaerobic process. CODCr removal rate improved significantly, increasing from 61.4% for the non-pretreated wastewater to 98.4% for the pretreated wastewater at the same wastewater dosage of 300mg/LCODCr. When the influent became the pretreated wastewater completely, CODCr removal rate reached 86%. In conclusion, alkaline decoposition-biological methane production process was technically feasible for the treatment of acetaldehyde wastewater.