The effect of reactive materials on the removal of organic contaminants in constructed wetlands

MSc. Mayang Christy Perdana

Doctoral thesis

Abstract:

Endeavors to mitigate organic contaminants in greywater, particularly micropollutants, through various approaches remain of interest. Greywater is known as one of the recyclable water sources for non-potable purposes. A concern arises when its potential reuse is challenged by the low potency of biodegradability. Meanwhile, Constructed Wetlands (CWs) have long-standing recognition as an alternative to conventional centralized wastewater treatment, but their performance in removing organic micropollutants varies across studies, and in some cases, still requires improvement. Some methodological criteria are of concern, yet the enhancement of complex abiotic and biotic mechanisms and practical feasibility are likely the most notable. The media-amendment approach could be one of the practical options, but a question may arise as to which media should be used. Reactive materials such as granular ferric hydroxides (GFH) and manganese oxides (MnOx) can be both implementable candidates for enhancing abiotic and biotic treatment processes via adsorption and redox facilitators. However, information on their capacity to enhance abiotic and biotic processes for organic micropollutant removal, and how they may respond to various factors in CWs is still limited. In addition, to the best knowledge, no studies have evaluated the potential role of functional gene abundance related to iron and manganese cycling in these processes. The main objectives of this study were: 1) to test the effectiveness of reactive materials used in CWs for removing organic contaminants, specifically those classified as organic micropollutants 2) to identify mechanisms that contribute to the removal of organic compounds in response to the use of reactive materials in CWs 3) to provide insight into how microbial communities are affected by reactive materials used in CWs, particularly associated with the removal of organic compounds 4) to observe the effect of plants on the performance of reactive materials-amended CWs. The study consisted of three experiments, and synthetic greywater spiked with selected compounds was used as influent. Experiment 1 tested the efficiency of MnOx used as media in CWs for the removal of 5-methylbenzotriazole (5MBTR), bisphenol S (BPS), metoprolol (MTP), and diclofenac (DCF) in greywater under different aeration conditions, including the presence of plants and an increased level of ammonium, taking into account seasonal temperature decline as an uncontrolled variable. The results showed that DCF was removed by MnOx regardless of temperature, achieving over 99% removal efficiency. This interaction was likely influenced by DCF’s comparatively low ionization potential (5.46) among other tested compounds. Meanwhile, 5MBTR, BPS, and MTP were more effectively removed by control (sand media), with temperature contributing 21–39% as a negative factor to their removals. Organic carbon deficiency likely became a limiting factor for compound removals in MnOx media. Variables such as the aeration, presence of plants, and increased ammonium could be considered to have a moderate to insignificant effect on compound removals. In experiment 1, unaerated treatment with sand and plant was considered the most resilient treatment, providing the highest average removal of 65%, 78%, and 95% for 5MBTR, BPS, and MTP, respectively. Chirality test of MTP revealed a similar trend of deviation in enantiomeric fractions relative to the influents, independent of the media type. Experiment 2 observed the dissipation rate (k, d-1) and half-life (DT50, day) via a modified OECD 308 test of selected compounds considering the effect of applied conditions (sterile vs non-sterile treatment), media type (reactive materials vs river sediment as control), the wastewater source (different solution type), and different planted treatment (from grow boxes with unplanted vs planted system). Autoclaving and microbial inhibitors were applied in sterile treatment. Additionally, abu

Abstract:

ndances of prokaryotic, fungal communities, and some functional genes in different media were analyzed, including those of iron and manganese-related genes. Results showed that the dissipation rate was mainly influenced by the effect of applied conditions, with non-sterile conditions exhibiting a higher dissipation rate for most compounds than sterile conditions. Of note, media type had a significant effect on the dissipation rate of BPS and DCF, with GFH and MnOx being the most prominent, respectively. The shortest median of DT50 values in non-sterile treatment for 5MBTR, BPS, DCF, MTP, and sulfamethoxazole (SMX) were 17.4, 21.3, 13.3, 15.5, and 10.5 days in GFH, GFH, MnOx, river sediment, and GFH, respectively. In general, biotic processes were observed to be major dissipation mechanisms of the target compounds regardless of the media type. However, abiotic processes might govern the dissipation of some compounds such as BPS (in GFH and MnOx) and DCF (in MnOx). In addition, non-sterile treatment showed greater variability of redox potential than the sterile treatment, indicating a progressive and dynamic environment. In experiment 2, the highest relative abundance of most evaluated iron and manganese-related genes (e.g., mnxG, mcoA, mtrA, and mtrB), was found predominantly in either GFH or MnOx. However, it appeared that the dissimilatory iron/manganese reduction was probably not the primary driver for the removal of the target compounds. This was likely due to potential competition with incomplete denitrification processes indicated by the higher relative abundance of nirK and nirS genes over nosZI and nosZII genes, among other factors. Experiment 3 evaluated the removal of multiple compounds in a vertical flow (VF) unsaturated Constructed Wetlands (CWs) system under declining temperature conditions using GFH and (MnOx)-filled PVC columns, considering plant interactions and microbial community responses. The enhanced effect of GFH and MnOx towards the removal of all compounds was +28% and +7%, respectively, while the effect of plants was pronounced in MnOx, with +7% of enhanced effect. The column with GFH-unplanted treatment was the most effective treatment among all counterparts, achieving around 20–100% higher average of removal efficiencies for most compounds compared to the control (sand-filled column). This improvement was particularly notable for the removal of ibuprofen, saccharin, cyclamate, sulfamethoxazole, furosemide, ketoprofen, bisphenol-s, gemfibrozil, hydrochlorothiazide, acesulfame, fluconazole, and diclofenac. Meanwhile, MnOx-planted treatment enhanced the removal of several compounds, with ibuprofen, furosemide, and diclofenac showing around 20–100% higher efficiencies than the sand-planted treatment. The evaluated gene abundance was affected by the type of media, with the highest levels of prokaryotic and fungal communities found in GFH-filled columns. The possible removal mechanisms were assumed to involve adsorption, oxidation by MnOx, Fe(II) oxidation (indicated by the highest relative abundance of the Fe-oxidizing gene (mtoA) and the lowest pH level in GFH), and microbial-related processes. Neither the presence of plants nor the interaction with media types significantly influenced the gene abundance. In addition, reactive materials demonstrated approximately 20% and 70% higher removal efficiency of DOC and phosphate, respectively, compared to the sand-filled column. This emphasizes their practical feasibility in CWs for greywater reuse. The system demonstrated resilience to seasonal temperature changes, particularly in GFH-amended media. Taken together, the described three experiments may help to bridge the knowledge gaps on how CWs-amended media with reactive materials interact with abiotic and biotic mechanisms, while also contributing to the consideration of their practical potential for future system upscaling.

Keywords

constructed wetlands, greywater, organic micropollutants, reactive materials

Language used: English

Date on which the thesis was submitted / produced: 12. 10. 2025

Thesis defence

• Supervisor: prof. Ing. Jan Vymazal, CSc.
• Reader: Hana Brunhoferová, externi, Ewa Felis, externi

Czech University of Life Sciences Prague

Faculty of Environmental Sciences

Doctoral programme:
Applied and Landscape Ecology