Study On Applying Anoxic-oxic MBR Process To High-strength Ammonia Wastewater Treatment

Nitrogen pollution has become a big problem to the health and survival of aquaticorganisms and human beings. It is an arduous task for environmental engineers todevelop more and more efficient, economic processes to solve this problem. On the basis of existed nitrogen treatment processes, an anoxic-oxic MBR waschosen to treat the high-strength synthetic ammonia wastewater. It meaned to makefull use of nitrification and denitrification as well as advantages of membranebioreactor (MBR) during the treatment. The experiment was divided into two parts according to sources of rawwastewater. At the first part, the influent was synthetic wastewater. In this part ofexperiment the average COD concentration and removal efficiency were 269mg/L and85%. And the ammonia concentration and removal efficiency were 63mg/L and 49%separately. However, the quality of influent caused sevious filamentous bulging ofactivated sludge and the maximum SVI was as high as 401mL/g, which restrained thegrowth of nitrifying bacteria, and brought bad effects on nitrogen removal. In addition,the sludge loading, C/N ratio, pH value and activity of sludge were main influcingfactors for nitrogen removal. In the second part, the influent was made by diluted domestic sewage added withammonium sulfate. Due to multiple microorganisms and trace elements supplied fromdomestic sewage, the sludge was active and average SVI was only 104mL/g. TheCOD removal was well and MBR showed an ability to resist impact loads, whichpromised the COD effluent to be lower than the reuse water standard. Because ofmembrane seperation, the COD value in mixed liquor was so high that membranefouling happened seriously. In order to insure normal operation, it was necessary tomake membrane cleaning frequently. The average ammonia concentration was436mg/L and its removal efficiency was as high as 89%. However, C/N ratio andshort hydraulic retention time caused nitrite accumulation in the reactor and rejectednitrogen removal, the maximum efficiency of which was only 50%. In order to solve the problem of membrane fouling, it was necessary to apply thephysical, chemical or biological processes to decrease the concentration of organicmatters in mixed liquor. Besides, from the experiment results, it was feasible to keepon the experiment with short nitrification-denitrification process in future. On thecondition of some modification such as adding carbon source, the nitrogen removalefficiency would likely be increased.