Study On Enhanced Anaerobic Digestion Of Oily Sludge By Alkaline Pretreatment Coupled With Zero-valent Iron

Wastewaters from chemical,pharmaceutical,coking and other industries often contain large amounts of oily sludge during biological treatment.These oily residual sludges are recognized as hazardous wastes.Improper disposal will pose a serious threat to the environment and human health.Anaerobic digestion is becoming a sustainable treatment technology to recover energy(methane)during the reduction of sludge.However,the residual sludge generated in the chemical sewage treatment process is different from municipal sludge,which causes anaerobic digestion to be inefficient.The reasons are as follows: First,the remaining sludge produced in the chemical wastewater treatment processes is complex and contains quite a lot of organic chemicals,such as aniline,petroleum,and organic chlorine,etc.,which are harmful to anaerobes especially to sensitive methanogens;The chemical sludge is of high viscosity and high emulsification degree,which is not conducive to microbial degradation.Long hydrolytic retention time during chemical wastewater treatment process means an increase of the sludge age,which makes sludge cell walls solid.As well known,breaking cell wall is the rate-limiting step of anaerobic digestion of waste sludge.Therefore,the anaerobic digestion of waste active sludge from chemical wastewater treatment process is difficult.In this study,the alkaline pretreatment of oily sludge was carried out to achieve the destruction of the sludge cell wall,and a large amount of intracellular organic matter was detected,thereby accelerating the hydrolysis of the sludge into dissolved small molecule organic matter and improving the anaerobic digestion efficiency.On the other hand,in order to solve the accumulation of excessive organic acids(such as propionic acid,etc.)generated by pretreatment,this study adopted the addition of zero-valent iron.The results of the study showed that the output of methane from oily sludge after alkali pretreatment increased by91.7%.With further experiments,it was found that pH = 9 was the optimal pH condition for pretreatment of oily sludge.The alkali pretreatment coupled with zero-valent iron powder methane production increased by 105.4%,and the sludge reduction rate increased by 13 percentage points.Alkaline pretreatment coupled with rusty iron filings can increase the methane production by 131.7%,and the VSS reduction rate can be increased by 16 percentage points.