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Removal of bisphenol A from wastewater and groundwater with helophytes

Christofilopoulos Stavros

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Summary

The presence of emerging organic contaminants (EOCs) in wastewater (WW) has attracted intense interest in the environmental engineering community, due to the high frequency of detection and the adverse effects on human health and the environment. EOCs consist of a wide range of substances, such as endocrine disrupting compounds (EDCs), pesticides and pharmaceuticals, such as antibiotics. EDCs are exogenous substances, which even in very small amount interact with the hormonal regulation and the endocrine system. On the other hand, the presence of antibiotics in the environment has raised increasing awareness, because they can potentially cause the selective proliferation of antibiotic resistant bacteria.Conventional WW treatment plants (WWTPs) have proven to be inefficient in the removal of EOCs, since they are not currently designed to cope with this type of contamination. Taking into consideration that nowadays WW discharges still constitute one of the major sources of EOCs in the environment, addressing this threat has become a top-priority task. Implementation of efficient advanced tertiary treatment techniques, are currently very energy- and cost-intensive technologies. Among alternative treatment technologies, constructed wetlands (CWs) are proposed as an environmentally acceptable method that exploits the synergistic effect of plants with the associated microorganisms for WW treatment, contaminated with EOCs. Current knowledge on the efficacy of the removal of EOCs with CWs and the effect of various parameters, is still limited.In this regard, the objective of this thesis is to investigate the potential of specific halophytes to remove the endocrine disruptor BPA from municipal wastewater and groundwater. Moreover, to evaluate the performance of two CWs planted with halophytes on the removal of selected EOCs. We focused on the contribution of plants on the removal, as well as the efficacy of the planted wetland as a whole system.Pot-scale experiments were performed, in order to have a first view of the role of Juncus acutus and Tamarix parviflora halophytes on BPA removal from contaminated soil. Estimation of the apparent degradation rate constant (k’) revealed the contribution of halophytes to the process. Degradation rates was found to be 1.94-2.47 10-2 in the planted and 0.71-0.98 10-2 mg BPA kg-1 soil h-1 in non-planted treatments.Following this, a hydroponic experiment took place with the helophyte J. acutus be exposed to mixture of contaminants: BPA, antibiotics ciprofloxacin (CIP) and sulfamethoxazole (SMX) and heavy metals (Cr, Cd, Zn and Ni). The aim was to evaluate the potential of J. acutus for use in CWs. Concentrations of the compounds ranged from μg L−1 to well beyond environmentally relevant values (50 mg L−1 for the organics and >1000 mg L−1 for Zn and Cr). J. acutus exhibited significant contribution on the removal of BPA, CIP and SMX. The resultant removal of BPA concentrations of up to 50 mg L-1 exceed 96%, after 28 days. J. acutus plants show the potential to accumulate heavy metals in both root and leaf tissues in considerable amounts.The aim of the next study was to simulate the treatment procedure of a contaminated shallow aquifer. A pilot unit of 1 m3 planted with J. acutus used spiked with BPA tap water that was recirculated, flowing from the bottom to the surface of the pilot, passing through the root zone. When the system exposed to initial BPA concentrations of 2.67 mg L-1 and 184 μg L-1 could not be detected after 15 days of treatment. After 5 experimental runs, the system was proved reliable and robust within reasonable input oscillations of the BPA concentration and inlet flow rate.Afterwards, evaluation of a small scale horizontal subsurface flow (HSF) CW fed with secondary treated WW from the WWTP of the city of Chania, was performed. The HSF of 0.5 m3 surface and 157 L working volume was planted with 5 Juncus acutus helophytes. The aim was to investigate system’s efficiency in terms of BPA and antibiotics removal, in short term experiments (approx. 14 days) and under different operating conditions. The influence of vegetation on BPA removal was highlighted after comparison with a non-vegetated unit. The ratio of BPA mass removed over the BPA mass entering the system (𝑚𝑝%) was 46% higher in the vegetated wetland. Superior treatment’s performance at hydraulic retention time (HRT) of 2 d was obtained: 𝑚𝑝 was 92% versus 48% at HRT of 1 d. The influence of HRT on CIP removal was less important. SMX was resistant to the removal and demonstrated unstable results. A slightly higher BPA removal efficiency in summer was not statistically verified.Finally, a pilot-scale HSF-CW study for the degradation of bisphenol A in primary-treated municipal wastewater, was undertaken for 7 months period. The average removal efficiency for BPA was 98% (mean influent concentration: 0.26 mg L-1) in the summer. Significant sensitivity in the system was observed with changes of HRT. For almost all the wastewater quality parameters, moderate removal efficiencies were measured.The overall outcome of this study is the significant contribution of Juncus acutus to the attenuation of BPA. It appears as a promising species for CW applications and is recommended for further investigation in the phytoremediation field.

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