|M.Sc Student||Dawas Anwar|
|Subject||Combined Adsorption and Biological Degradation Processes for|
Removal of Pharmaceutical Compounds from Effluents
by Nitrifying Bacteria
|Department||Department of Civil and Environmental Engineering||Supervisors||Professor Emeritus Carlos Dosoretz|
|Dr. Isam Sabbah|
|Full Thesis text|
The occurrence and fate of pharmaceuticals active compounds (PhACs) in the water environment have been recognized as one of the emerging issues in environmental chemistry due to their potential to cause undesirable ecological and human health effects. PhACs have been detected ubiquitously in water environments and water distribution systems because of their high persistence and low adsorption properties. Because these chemicals are often present in wastewater at concentrations ranging from 0.1 to 105 ng/L, they cannot support cell growth and activity of organisms capable of mineralizing them during biological wastewater treatment.
The main objective of this study was to examine the extent and pattern of biotransformation of PhACs at environmental (µg/L range) and above-environmental (mg/L range) concentrations by means of free and entrapped nitrifying bacteria grown under strict autotrophic conditions. Bacterial entrapment by combining adsorption with powdered activated carbon (AC) was also studied. Nitrifying bacteria are known for the co-metabolic ability of a wide range of organic substrates, including PhACs, by means of ammonia monooxygenase (AMO) in ammonia-oxidizing bacteria (AOB). Entrapment is expected to protect the nitrifying bacteria from environmental competition. Five selected pharmaceuticals?Ibuprofen (IBP), Ketoprofen (KTP), Carbamazepine (CBZ), Dexamethasone (DXM) and Iopromide (IOP) were applied as model compounds at concentrations between 20 to 3000 µg/L.
The biotransformation experiments showed a clear removal of the model compounds. Complete biotransformation was observed for IBP and KTP whereas the removal of DXM reached 50%, CBZ reached 40%, and IOP 10%. The faster rate of biotransformation was observed for IBP and the slower one for IOP, in accordance. Hydroxylated IBP was the main biotransformation product accumulated indicating AMO is the enzyme responsible for biotransformation. Based on these results, an efficient elimination of pharmaceuticals present at trace concentrations can be achieved by nitrification. The metabolic succession of the compounds (IBP>KTP>CBZ>DXM>IOP) correlated their diffusion flux across the bacterial membrane. This correlation provides a practical approach for structure/activity-relationship predictions.
The combination of PAC within the immobilized matrix of nitrifying bacteria led to a significant enhancement of the removal rate of all model compounds. This result can be attributed to the synergism between adsorption and biodegradation processes. For Ibuprofen, the most readily degradable compound studied, the biotransformation rate is only slightly increased by PAC, suggesting that adsorption and transformation are of similar magnitude. More experimental examination is still required to better assess the mechanism of the PhACs removal through combined adsorption and degradation.