Coated magnetite nanoparticles as a potential booster for light-expanded clay aggregate substrate in constructed wetlands : adsorption of heavy metals and transport behavior in porous media

Mlih, Rawan; Klumpp, Erwin (Thesis advisor); Schäffer, Andreas (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

Wastewater treatment technologies such as constructed wetlands (CWs) are considered a viable alternative to conventional treatment systems. Pollutants removal in CW is achieved through integrated biological, chemical, and physical mechanisms. The substrate, which makes up the filtration bed in CW, plays a leading role in the purification process. Light-expanded clay aggregates (LECA) have been extensively investigated as a substrate for CWs worldwide. In this thesis, a literature review was conducted to summarize the current literature on LECA-based constructed wetlands. Removal performances for main wastewater components such as phosphate, nitrogen species, suspended solids, and oxygen demand were highlighted. The physical and biological water purification processes in LECA wetlands are discussed with additional emphasis on its design and layout for different types of wastewaters, and under different climatic conditions. Other considerations in the review were highlighted, such as LECA’s life cycle including sourcing, production energy demand, reuse, and recycling options for spent LECA. Research and development opportunities were identified for structural and compositional LECA modification to obtain tailored substrates for the use in water treatment and specific treatment tasks. The review revealed insufficient literature on heavy metals adsorption onto LECA. Existed studies are restricted to particular heavy metals with rather limited adsorption capacities. In this thesis, the adsorption potential of a novel poly(acrylic-co-maleic) acid coated magnetite nanoparticles (PAM@MNP) for Pb2+ and Cu2+ removal from an aqueous solution was investigated. It was argued that the physicochemical stability of PAM@MNP is better than that of other coated MNP, i.e., PAA@MNP. This renders PAM@MNP more favorable to use for heavy metal removal. The adsorption kinetics data showed that PAM@MNP attained sorption equilibrium for Pb2+ and Cu2+ metals after 60 minutes. In addition, they could be fitted accurately by pseudo-first-order kinetics model. The calculated Langmuir maximum adsorption capacities were 518 and 179 mg g−1 for Pb2+ and Cu2+, respectively (equal to 2.50 and 2.82 mmol g−1 for Pb2+ and Cu2+, respectively). The results indicate that PAM@MNP is a very attractive adsorbent for Pb2+ and Cu2+ metals at an optimal pH value of 6 and can be applied to remove heavy metal cations from wastewater. Understanding the physicochemical factors affecting nanoparticles transport in porous media is critical for their application in soil or other media system. Hence, the transport and retention of PAM@MNP using water-saturated columns filled with quartz sand as a model media were studied in the following study. The results showed that the mass recoveries in the column effluent ranged from 45.2 to 99.3%. The highest relative retention of PAM@MNP was observed for the lowest initial concentration (Co). Smaller Co also resulted in higher relative retention (39.8%) when IS increased to 10 mM. However, relative retention became much less sensitive to solution IS as Co increased. The high mobility is attributed to the PAM coating provoking steric stability of PAM@MNP against homoaggregation. PAM@MNP retention was about 10 folds higher for smaller grain sizes, i.e., 240 µm and 350 µm versus 607 µm. The simulated maximum retained concentration on the solid phase and retention rate coefficient (k1) increased with decreasing Co and grain sizes, reflecting higher retention rates at these parameters. The study revealed under various IS for the first time, the high mobility of polymer-coated magnetite nanoparticles at realistic (<10 mg L−1) environmental concentrations. The revealed high adsorption capacity for Pb2+ and Cu2+, and the enhanced mobility of PAM@MNP in porous media are promising key aspects for these nanoparticles to be applied in integration with LECA substrate in CWs. In preference to LECA, the attained affinity to the investigated heavy metal cations makes PAM@MNP a good candidate as a coating material for LECA granules, the final product i.e., coated LECA with PAM@MNP, can be installed as a filter bed in CWs targeting heavy metal cations removal. However, further research is essential to test the compatibility of these nanoparticles as a coating material for LECA and their subsequent application. Additionally, building on the enhanced mobility of PAM@MNP in the porous media, it can be concluded that PAM@MNP can provide a solution for regenerating the saturated LECA with pollutants in CWs by being injected into the system.

Institutions

• Department of Biology [160000]
• Chair of Environmental Biology and Chemodynamics [162710]