Microplastic (MP, < 5 mm) and nanoplastic (NP, < 1 µm) pollution has become a growing environmental concern, as they are detected everywhere, including in surface waters used for drinking water (DW) production. Recently, NPs have been detected in finished DW, indicating incomplete removal by DW treatment plants (DWTPs). Coagulation-flocculation-sedimentation (CFS) is a promising treatment technique, but current research lacks connection to practice and/or mostly focuses on MPs. This thesis investigates the influence of coagulant type, dose, and NP size on NP removal during CFS. The research connects to practice by using coagulants and doses used in the Dutch DWTPs.

A survey with four Dutch DW companies provided insight into the CFS procedures. Jar tests simulated CFS in the lab, using ferric chloride (FeCl₃), aluminium chloride (AlCl₃) and polyaluminium chloride (PAC) to assess the impact of coagulant types. Theoretical optimum doses were compared to practical doses (obtained from survey) to determine the influence of the coagulant dose. Lastly, the effect of NP sizes on CFS removal efficiencies was studied using 200, 500, and 1000 nm NPs. All experiments were done with NPs spiked in tap water. CFS efficiency was evaluated through turbidity, pH, alkalinity, UV-VIS, residual coagulant and ζ-potential measurements.

PAC was identified as the most efficient coagulant considering all evaluated parameters. Theoretical doses, which were higher than practical doses for FeCl₃ and AlCl₃, achieved more effective NP removal than practical doses. Charge neutralisation was confirmed as the main mechanism for NP removal. Lastly, although particle size is generally thought to affect NP removal, this study’s results did not allow for confirmation or refutation of this statement. Overall, this research highlights that the type of coagulant and dose can influence NP removal in DWTPs. These findings can be a first step to help DWTPs optimise CFS for more NP removal.

A novel activated carbon-iron composite material has been developed as an adsorbent for water treatment. Due to its activated carbon (AC) content, the material could be used to remove pollutants such as organic micropollutants (OMP). Fast AC bed exhaustion makes adsorption a cost-intensive solution. Regeneration of AC is done off-site and requires transport and high energy consumption for heat treatment. Due to the iron and graphite content of the novel adsorbent, catalytic regeneration could allow for in-situ regeneration. This property would present a major advantage over common AC. Regeneration could potentially be realized by applying an electric current across an exhausted bed of this adsorbent. Such a setup is called a “particle electrode”, where electrically conductive particles are placed between an anode and cathode. Upon application of an electric current across an exhausted bed of adsorbent, two mechanisms are hypothesized to result in the restoration of adsorption capacity: (1) desorption and (2) degradation of the pollutant. This study evaluated the adsorption capacity and rate constants for 17 OMP on two different versions of this partly graphitized carbon (with and without iron content) as an alternative to conventional AC for drinking water treatment. By batch adsorption experiments, the adsorption properties of this novel carbon were investigated. Oxidation of zero-valent iron on the iron containing version of carbon resulted in yellowish water. This version was therefore considered not appropriate for general drinking water treatment, and the remaining experiments were conducted only with the version without iron. The material adsorbed a great variety of OMP, including different charges and hydrophobicity. Its graphite content probably promoted the adsorption of neutral compounds. A negatively charged layer formed by NOM accumulation on adsorbent surfaces assisted positively charged compounds adsorption. Investigation of regeneration efficiency was conducted with alternative cycles of adsorption and regeneration with high OMP concentration solutions. This material could be electrochemically regenerated. Reverse adsorption could be achieved on neutral, positively and negatively charged compounds in multiple cycles of regeneration. Electrodesorption is probably the major mechanism responsible for regeneration. Permanent and partial loss of adsorption capacity was recorded, probably due to poor NOM desorption and change in surface chemistry. Regeneration efficiency was not positively correlated with elevating applied current. Increasing cell voltage is not always beneficial to the electrochemical process. Prolonged treatment time improved the regeneration efficiency, but the marginal benefit was considered to be uneconomical. Poor NOM regeneration was responsible and more concerning for the loss of adsorption capacity. Long-chain PFAS regeneration was achieved over cycles of regeneration. Short-chain PFAS regeneration was unfavorable due to blockage of micropores.

Surface water tracing experiments help to identify the flow paths of in-stream mass transport. This provides useful information for developing mitigation measures for contamination, and thereby for solving environmental problems. Salts, fluorescent dyes and isotopes are commonly used tracer substances.
However, it is well known these tracers have several drawbacks, including, for example, a finite number of unique tracers with similar transport properties, which limits the possibility to repeat an experiment due to system memory. Additionally, it is difficult to perform multi-tracer experiments, due to a lack of specificity. Lastly, the detection limit becomes an important constraint when using a tracer in larger water bodies or over longer travel distances, due to the vast dilution. The recently developed silica encapsulated synthetic DNA nanoparticle with a superparamagnetic core (SiDNAMag), can theoretically overcome the aforementioned limitations of existing tracers. SiDNAMag particles can be recovered from a sample by magnetic separation. This limits the influence of water quality on the qPCR analysis and provides an easy
method for up-concentration of samples. However, with the presence of natural colloids, particulate matter,
and river bed sediments, SiDNAMag particles are likely to undergo complex interaction processes in addition to
dispersion and advection. Moreover, little is known about the possible SiDNAMag tracer sinks during transport.
The focus of this work is to identify the transport behaviour of the SiDNAMag tracer in terms of breakthrough
curves (BTC) and hydrodynamic dispersion as well as to study the interactions with the natural environment,
specifically water quality and sediments. This was investigated by comparing SiDNAMag particles to NaCl,
a widely used solute tracer, and silica microparticles. To do so, open channel injection experiments using
SiDNAMag particles were performed in the laboratory in different river water types and with the presence of
sediments at the channel bottom. The resulting BTCs were interpreted with a 1D advection and dispersion
model with transient storage (OTIS), to determine the hydrodynamic dispersion coefficient. Mass recovery
was calculated by integrating the BTC.
The results show that SiDNAMag particles have a reproducible but different transport behaviour than
NaCl solutes. The SiDNAMag particles arrive, peak and return to background concentrations earlier than NaCl
solutes. Furthermore, the interpretation of the data with a 1D advection and dispersionmodel showed that the
dispersion coefficient for SiDNAMag was lower (0.34E-3m2/s – 0.88E-3m2/s) than that of NaCl (0.81E-3m2/s
– 2.31E-3m2/s). Literature on solutes and colloids in the aquatic environment supports the possible difference
in the transport behaviour of solutes and colloids. No relation between the transport behaviour and presence
of bottom-sediments was found. The mass recoveries for SiDNAMag experiments were between 36% and
131%, which could be partly explained by the bottom-sediments which detained between 0.16% and 16.94% of
the SiDNAMag mass during the experiments. No relationship was found between the three natural water types
and the observed mass losses. Additionally, the silica microparticle injection experiment showed the same BTC
characteristics for silica microparticles as SiDNAMag though without mass loss, indicating mass loss occurred
in the lab analysis. Due to the uncertainties in the lab analysis, no accuratemass recovery for the SiDNAMag
tracer could be calculated. Furthermore, the observed scatter in the measurement data could be explained
by the uncertainties in lab analysis as well as possible differences in transport behaviour of solutes and colloids.
In conclusion, the results of the laboratory experiments with the SiDNAMag particle show that it is a
promising hydrological tracer in surface water tracing experiments to trace colloids. Thereby it can be a
valuable tool to gain information on the movement ofmicroparticles, like microplastics and pathogens, in the
natural environment. The next step towards achieving this goal is performing a field experiment, for which
upscaling of the SiDNAMag tracer production is required.