Potential of horseradish hairy roots for the phytotreatment of water containing sulfamethoxazole

The continuous accumulation of micropollutants in water is a growing problem for our water resources. Currently, most conventional wastewater treatment plants (WWTP) are not able to remove them efficiently. Several pharmaceuticals, for which the measured concentrations in German surface water might have an effect on some living organisms, are included in this pollutant class, as for example sulfamethoxazole (SMX), carbamazepine (CBZ) and diclofenac (DFC). Phytoremediation is known as an emerging and advantageous technique for soil and water remediation. The potential of using horseradish hairy root cultures (HR) as a plant model for the study of SMX phytoremediation has already been pointed out in a previous work and was tested again in this work, with the addition of a temporal scale (1, 2 and 6 days of contamination). The experiment confirmed the potential of using horseradish HR for SMX phytoremediation, with a disappearance rate from the medium around 90% already after 1 day and close to 100% after 6 days. A novel metabolite (SMX-Glycoside) was also detected in the medium as well as in the HR (concentration measurement with LCMS). Moreover, an enhancement of detoxifying enzymes and no enzymatic stress symptoms could be observed (enzymatic activity measurements with a spectrophotometer). Given that, in real life, SMX is not the only pharmaceutical present in WWTP influents, a second experiment was carried out with a mix contamination (SMX, CBZ and DFC). Although some differences of the SMX fate and of the enzymatic activity were observed, the potential for SMX phytoremediation could be confirmed also in this case (disappearance rate higher than 80% after 1 day and close to 100% after 6 days). DFC was also taken up and metabolized in the analyzed time period, whereas a lower disappearance rate was observed for CBZ. This experiment permitted thus to confirm the potential of using horseradish HR for SMX phytoremediation and to extend it also to a mix contamination (SMX and DFC).

Enhancing the photo-Fenton treatment of contaminated water by use of ultrasound and iron-complexing agents

Stefanos Papoutsakis

The photo-Fenton process is a promising emerging technology for the treatment of contaminated water streams. It is based on the generation of reactive oxygen species that are capable of destroying recalcitrant contaminants otherwise unaffected by conventional municipal wastewater treatment method. Among its innate advantages are that it can be catalyzed naturally by solar radiation and the main reagents required are iron and hydrogen peroxide, both abundant and relatively cheap. There are however some important limitations. The process functions best at acidic pH, is negatively affected by some inorganic ions present in natural water and the water requires pH neutralization and iron recuperation following the treatment. These limitations inhibit the application of the process at larger-scale. This work is an attempt to develop new strategies for enhancing the photo-Fenton process for making it a more attractive option for the treatment of municipal or industrial wastewaters. Two main pathways are investigated, the use of ultrasound and the use of iron-complexing agents. Ultrasonic processes have been shown to improve degradation kinetics when applied in combination with photo-Fenton, while at the same time are not as negatively affected by some of the inorganic ions present in water. Iron-complexing agents can maintain iron soluble at a wider operational pH and can also improve process efficiency via pathways discussed at length in the text. Chapter 2 is focused on the application of ultrasound in combination with photo-Fenton for two very distinct applications: 1) A pilot-scale ultrasound/photo-Fenton system was set-up and evaluated for the treatment of three different contaminants with distinct physicochemical properties and at different concentrations. Synergy was evaluated in terms of degradation kinetics and H2O2 consumption efficiency. 2) Ultrasound was applied alone and in combination with photo-Fenton for the treatment of the iodinated contrast agent Iohexol. These agents are injected in patients during radiographic procedures and excreted via urine. This provided an opportunity to examine if ultrasound could improve their treatment in such a complex aquatic medium. Treatment options both in urine (at the source) and in the context of municipal wastewater are discussed. Chapter 3 is focused on the use of EDDS as an iron-complexing agent for degrading contaminants at near neutral pH across a concentration range usually found in different wastewaters (from ÎŒg L-1 to mg L-1 ). EDDS was used both for the treatment of microcontaminants (ÎŒg L-1) in municipal wastewater treatment plant effluents as well as for highly contaminated ( several mg L-1) water. The importance of several factors and operational conditions is discussed. Chapter 4 discusses the possibility of exploiting natural iron-complexing agents (mainly phenolic/polyphenolic compounds) that can be found in some types of wastewater (e.g from natural products processing industries). The concept of reusing polyphenol-rich wastewater in small quantities as an alternative to artificial complexing agents is introduced. As a case study, water containing highly concentrated cork bark extracts (Cork Boiling Wastewater) has been added in natural water spiked with one or several contaminants. Its capacity to maintain Fe3+ soluble at near-neutral pH as well as the effect on Fenton/photo-Fenton degradation were observed.

EPFL2016

Enhancing the photo-Fenton treatment of contaminated water by use of ultrasound and iron-complexing agents

Stefanos Papoutsakis

EPFL2016