Study On VOCs Distribution Of Refining Sewage In Aeration Tank And Influencing Factors

VOCs from refinery sewage are important sources of odor pollution and have a great harm to atmospheric environment and human health.Activated sludge process is one of the main methods of refinery wastewater treatment.And the key parameter to control VOCs from activated sludge system is keeping the system in reasonable conditions.In this paper,benzene,toluene and xylene are used as three targets contaminants of benzene series in the three-phase distribution system.The impact of water quality parameters and hydraulic conditions on distribution of benzene series in the three-phase system are researched by methods of orthogonal and single factor experiment.The main conclusions are as follows:Orthogonal experiments results of benzene series including benzene,toluene,xylene show that water quality parameters affecting the benzene series volatilization with a descending sequence:Ammonia>COD>pH;the hydraulic condition effecting benzene series volatilization with a descending sequence:Aeration intensity>MLSS>HRT.When the pH of refining wastewater is extreme,the low microbial activity resulting in low absorption ability of benzene series,so the volatile quantity stays at low level,when the pH=6⁹,the microbial degradation gradually dominating the fates of VOCs with the increase of the microbial activity,benzene series are degraded to inorganic,this leads to a small volatile quantity amount of VOCs.Keeping the pH at=8⁹ can prevent the volatilization of VOCs effectively.When COD stays at low level,the capacity of microbial degradation is low because of lacking organic matter.On the opposite,the high level of COD makes microorganism metabolic reaction though simple linear organic matter.Keeping COD=400mg·L^-1 can prevent the volatilization of VOCs effectively.Ammonia can promote the volatilization of benzene series in refining sewage significantly,the higher ammonia concentration,the bigger volatile quantity.Keeping ammonia concentration at a low level can prevent the volatilization of VOCs effectively.Aeration can promote the volatilization of benzene series in refining sewage,this trend is obvious when aeration intensity stays in high level.But when it stays at low level,aeration intensity may not meet the demand for dissolved oxygen in activated sludge.Keeping the aeration intensity at 0.4 L·min^-1 can prevent the volatilization of VOCs effectively.Sludge concentration determines the degradation efficiency of the benzene series in activated sludge directly,when it sludge concentration is low,there small amount of microorganisms involved in degradation which lead to a low degradation efficiency.On the opposite,the high level of sludge concentration may leads to poor ventilation and even produces new volatile organic compounds because of anaerobic fermentation.Setting the sludge concentration at 3000mg·L^-1 can prevent the volatilization of VOCs effectively.The HRT is too long or too short will affect the treatment effect because of the reaction contact time.Keeping the hydraulic retention time at 10¹2 h can prevent the volatilization of VOCs effectively.Benzene series show great difference in volatilization and mass distribution proportion in gas,liquid and activated sludge phase.Most of the meta-xylene are adsorbed in activated sludge,both of the benzene and toluene show a large volatile content in gas phase,benzene shows better between two of them,which is caused by differences in the molecular structure of the three.And the activated sludge shows great difference between adsorption degradation ability of three kinds of benzene series.