Τύχη των φαρμακευτικών ουσιών κατά την επεξεργασία υγρών αποβλήτων με διεργασία ενεργού ιλύος και κατά την διάθεση τους σε υδάτινους αποδέκτες και στο έδαφος

Abstract

The study of the effect of pharmaceutical substances, as well as their persistence in the environment, has received an increasing interest in the recent years. Pharmaceutical substances used by humans, as well as their metabolites, enter the Sewage Treatment Plants (STP’s) through discharges from production facilities, hospitals and private household effluents. The most likely fate of these substances, provided that the sewages undergo (like all xenobiotic substances) biological treatment, may be one of the following: • The pharmaceutical substances or their metabolites are mineralized by microorganisms to carbon dioxide and water. • The pharmaceutical substances or their metabolites are more or less persistent in the STP, which implies that depending on their lipophilicity, the substances will be partly retained in the sludge or they will remain dissolved in the aquatic phase. The substances that will neither be retained, nor degraded in the STP, easily reach the aquatic systems. • The pharmaceutical substances, in case they are adsorbed on the sludge, if the sludge is used as a soil amendment, may be dispersed on agricultural land. The substances that are mobile in the soil may reach the ground water or leach to a nearby stream. The rest will be retained by soil. Most drugs are designed to be resistant and to maintain their chemical structure, as well as their biological activity, so that they can perform their therapeutic task. All of these factors, together with their continuous discharge, cause them to remain in the environment for significantly extended times, with adverse effects on the aquatic and terrestrial ecosystems. Direct or indirect water reuse leads to accumulation of pharmaceuticals to concentrations much higher than those of the original discharge. In the present work six pharmaceutical substances (propranolol, diclofenac, sulfamethoxazole, clofibric acid, carbamazepine, ofloxacin), which have been found in the effluents of STP’s (France, Greece, Italy, Sweden) in concentrations of the order of micrograms per litter, were examined. Their fate, in all the likely paths that can follow during their disposal in the drainage, such as the process of activated sludge, seawater, fresh water and soil, was studied. The biodegradation of the aforementioned substances was studied during the process of activated sludge as well as when discharged in aquatic (sea and brackish water) receivers. The adsorption capacity and the mobility in two different types of soil, and in the aerobic and anaerobic sludge of the subject substances was investigated. The subject pharmaceutical substances with the sole exception of sulfamethoxazole, were found to be particularly persistent both in the aquatic systems and during their treatment with activated sludge. The biodegradation of sulfamethoxazole was achieved under aerobic conditions in which the substance served both as carbon and nitrogen source for the enriched consortium (i.e. whenever there was a shortage of a carbon or a nitrogen source). As far as the adsorption of the subject substances on soil and on sludge is concerned, the distribution coefficients measured varied depending on the nature of substance and solid material. Ofloxacin was particularly strongly adsorbed (except for the case of using anaerobic biomass for the solid matrix), while clofibric acid was found to be weakly adsorbed. The adsorption of subject substances proved to depend considerably on the pH of system and on the ionic strength. Finally, the fate of pharmaceuticals in soil was also assessed using lysimeter studies. Important parameters investigated included: the pharmaceutical loading rate and the hydraulic loading rate for adsorption and the rate and duration of a “rain” event for desorption. Significant differences in the mobility of the six pharmaceuticals were found and they were correlated with the adsorption/desorption properties of the compounds, the amount of drug applied, the intensity of the “rain” events and the type of the soil.