Phytoremediation of pharmaceuticals in sewage using pilot sub-surface flow constracted wetland

Abstract

Phytoremediation is a method for cleaning up a wide range of environmental contaminants or a process where plants degrade pollutants through plant uptake and metabolic process. Pharmaceuticals that are excreted by consumers are incompletely eliminated in wastewater treatment plants and the considered major source of pharmaceutical pollution in aquatic environments. Current wastewater treatment plants are not specifically designed to eliminate and remove micro-pollutants completely. In this study, a pilot horizontal continuous sub-surface flow system designed constructed wetland was used to remove two emerging pharmaceuticals compounds (ibuprofen and paracetamol) from sewage at different concentrations (600 and 60 μg/L, respectively) using native plant species, Scirpus grossus. This study specifically aimed to determine the phytotoxicity and capability of the plant species and its interaction with associated rhizosphere bacteria to remove ibuprofen and paracetamol, and finally to optimize the performance of the pilot CW for maximum removal of the two compounds. The horizontal sub-surface flow continuous system was examined for its efficiency to remove mixed ibuprofen and paracetamol, S. grossus tolerance, and survival until 72 days, using various hydraulic retention times (HRT) at 3, 4, and 5 days and aeration rates at 0, 1, and 2 L/min. The extraction and detection methods were simplified and optimized without conditioning and equilibration for solid-phase extraction (SPE), and high-performance liquid chromatography (HPLC), and optimal hydraulic retention times (HRT) for ibuprofen and paracetamol removal to acceptable levels were assessed at retention times of HRT 5 days with removals of COD 94 %, NH3-N 99.7 %, NO3-N 96.6 %, and PO4 3- 83 % showed better performance than retention times of HRT 3 and 4 days. After testing for phytotoxicity, the highest removal of ibuprofen and paracetamol from wastewater were obtained in constructed wetlands aerated at 2 L/min with removal of 99.3% and 94.0% for pharmaceuticals concentration (600 μg/L ibuprofen, and 60 μg/L paracetamol) respectively, at the end of the exposure period after 21 days at HRT 5 days, in sand was 98.5% and 87.2%, with accumulation at shoot and root were 69-132 and 69-197, and 36-48 and 39-73 μg/kg at HRT 5 days, respectively. In addition, the study of rhizobacteria on S. grossus roots was identified as one of the phytoremediation mechanisms by rhizodegradation involving microbial around the plant roots. Three bacteria were isolated and classified as Enterobacter aerogenes, Bacillus flexus and Paenibacillus alvei, based on a microbial analysis, the three rhizobacteria had the capability to degrade ibuprofen and paracetamol with a degradation percentage of 88.0, 75.0, and 93.0%. The response surface methodology (RSM) was employed to optimize three operating variables. The optimum condition for phytoremediation process was determined at HRT 5 days with a retention time of 18 days and aeration rate at 2 L/min with a maximum pharmaceutical removal up to 97%. A validation test at the determined optimum condition was run with and without the addition of the three isolated rhizobacteria and had improved ibuprofen and paracetamol removal in water and sand up to 93.0,92.0 and 89.0,95%, respectively. Therefore, S. grossus was able to remediate wastewater containing a mixture of pharmaceuticals with the aid of rhizobacteria that degrade pharmaceuticals.