This thesis provides knowledge on factors affecting the representativeness of wastewater-based epidemiology (WBE) for monitoring the SARS-CoV-2 virus. The application of WBE to monitor health parameters has become essential due to the COVID-19 outbreak in March 2020. WBE is a well-known method to track the SARS-CoV-2 virus in wastewater and is used as an early warning system for the spread of the virus. However, the accuracy of monitoring trends through WBE is affected by various methodological challenges. This thesis aims to identify and quantify factors that affect the representativeness of monitoring the SARS-CoV-2 virus through WBE as part of the National Sewage Surveillance (NRS). Factors that possibly influence the representativeness of WBE for monitoring the SARS-CoV-2 virus from loo to lab are identified. To what extent these factors potentially affect the representativeness is discussed in a literature review. The results are presented in a dendrogram, showing the relationship between different factors. Based on the results of the literature review, the seven most important factors affecting the accuracy of monitoring SARS-CoV-2 through WBE were determined to investigate their effect in more detail. To create an overview of the effect of the various factors and to ensure comparison, the results of the different factors are synthesized based on four criteria. The effect on the representativeness is quantified and synthesized for the following factors: location of shedding, temporary in-sewer storage, RNA decay, deviant flow values, loss of information by overflow events, automated samplers and flow rate measurements. The effect of each factor is quantified individually. Different methodologies were used for the quantification of the different factors. The results were based on data analysis and expert consultations. It was observed that the effect on the load of SARS-CoV-2 monitored by temporary in-sewer storage is negligible, as well as the effect by the decay of SARS-CoV-2 RNA by temperature and residence time. For the following factors, the influence on representativeness may be significant: The location of shedding, deviant flow values, loss of information by overflow events, automated samplers and flow rate measurements. Based on the results of the synthesis an advice is given on which factors should be included in the methodology of monitoring the virus through WBE and which samples should be excluded. In conclusion, WBE is a valuable method to use for pandemic preparedness and monitoring health indicators from wastewater. There are many factors that influence the representativeness of samples for the monitoring of the SARS-CoV-2 virus. This research adds knowledge to the understanding of factors influencing the accuracy of WBE. The results elaborated by this study hope to contribute to the early detection of, not only, the SARS-CoV-2 virus, but also for other epidemic viruses, as well as other health indicators.

Of the world's population, 59% of the people are not connected to a sewer system and use on-site sanitation (OSS) systems. A large amount of these systems is unsafe. The ultimate goal of this research is to gain knowledge on manners to improve and monitor the safety of on-site sanitation (OSS) systems. The performance and safety of OSS systems are highly dependent on the level of faecal sludge in OSS system which is largely dependent on the accumulation rate of the sludge. However, scientists have not found a simple method to assess the accumulation rate of sludge. Knowing the sludge accumulation rate and therefore, knowing how quickly a tank fills, makes it possible to the necessary time between two emptying events or, with other words, the required emptying frequency. With the research presented in this thesis, a dynamical approach to viewing and assessing the status of OSS systems is developed in the form of a model by combining sludge accumulation theory and only a small number of in-field measurements. The modelled simulation of sludge accumulation shows highly similar results to empirical sludge accumulation studies. On the basis of the model, also a user-friendly tool has been developed that allows tank owners, policymakers or regulators to get personal recommendations regarding the emptying frequency of their OSS systems. This offers a new approach and with that an improvement of the way OSS system can be safely managed and monitored. This thesis provides evidence for the feasibility of constructing a numerical model as a measure to simulate sludge accumulation in OSS systems that can lead to emptying frequency recommendations. The results of this thesis can help in obtaining safe sanitation throughout the world and is aimed to contribute to achieving the United Nation’s Sustainable Development Goal 6.2.

Biofilters are increasingly being implemented in urban environments to treat stormwater but knowledge on their pathogen removal capacity at field scale is limited. Adequate pathogen removal is, however, needed if treated water is reused. This research evaluates the fate of Escherichia coli, enterococci and Campylobacter in a field scale biofilter in Rotterdam. This biofilter is part of the Urban Waterbuffer Spangen that combines biofiltration with Aquifer Storage and Recovery (ASR) to provide irrigation water for Sparta’s sports field. Microbiological water quality was analysed to assess the removal capacity of the biofilter. To identify factors causing adverse treatment performance, system construction, and operation were investigated, water flows in the biofilter were assessed, and hydraulic conductivity was measured. Lastly, model simulations were used to investigate how short-circuiting and event frequency and duration affect microbiological outflow concentrations. Results showed leaching of enterococci and Campylobacter and minimal retention of Escherichia coli. Leaching is likely caused by secondary contamination with bird faeces and multiple design and operational choices lead to low microbial retention. Coarse filter media results in high hydraulic conductivity, and consequently, short hydraulic retention times. Electrical conductivity measurements revealed short-circuiting pathways between the inlet and outlet. Lastly, uneven distribution of feed water presumably reduced the effective reactor volume. It is recommended to upgrade biofilter design by incorporating small particles in the filter media and maximizing the distance between the inlet and outlet. Additionally, reintroduce a ponding zone and rearranging event frequency and duration to lower microbial outflow loads is advised. Model simulations suggest that short, frequent events are beneficial to control microbial loads. However, further work to clarify microbial decay rates is recommended. To conclude, results imply that the biofilter is currently unable to improve the microbiological water quality but can become a treatment barrier if design and operation are upgraded to tackle encountered problems.

Due to increasing water consumption and stress on natural water resources, enhanced treatment of wastewater and reuse of water are becoming more important. Treated municipal wastewater has potential to be used for irrigation purposes, but pathogens are a major concern to protect environmental and human health. Therefore, an advanced treatment step is required to reduce the levels of microorganisms, nutrients and suspended solids. This literature review focusses on electroflotation (EF) as disinfection method of secondary municipal wastewater treatment. EF is a combination of electrocoagulation (EC) and dissolved air flotation (DAF). In EC treatment, a sacrificial metallic anode releases metal ions (usually iron or aluminium) into the solution while hydroxyl ions and hydrogen gas are produced at the cathode. Coagulants are created in situ by the hydrolysis of these metal ions to hydroxides that can destabilize pollutants. DAF is an adsorptive bubble separation process where generated gas bubbles (of 10-100 µm) separate the impurities by flotation. This paper outlines the processes involved in EF technology and its applications in (waste)water treatment. Therefore, the processes of EC and DAF are discussed first. Influencing parameters such as electrode material, pH, retention time, charge dosage, charge dosage rate, bubble formation and size are discussed, as well as pollutant removal mechanisms. The main mechanisms responsible are charge neutralization, adsorption, sweep coagulation, microbial destruction by the electric field and deactivation by free radicals. The conclusion is drawn that the hybrid EF technique, which has been implemented in different water treatment processes, promises to increase removal efficiencies compared to single EC and DAF treatment, but the full potential of EF as a tertiary treatment step for secondary municipal wastewater effluent is yet to be fully realized. The process needs to be empirically optimized, a challenging task due to the involvement of complex chemical and physical processes.

Drinking water distribution systems (DWDSs) are intended to supply hygienically safe and biostable water for human consumption. To supply aesthetically pleasant drinking water at the customers tap, water treatment and supply requires energy for production and distribution purposes (e.g. overall between 0.47 kWh/m3 in the Netherlands). On the other hand, DWDSs also contain thermal energy as a surplus of cold or heat. Depending on the drinking water temperature within the distribution network, thermal energy can either be used for heating or cooling purposes. Thermal energy recovery potential from drinking water has been explored recently. Cold thermal energy recovery from drinking water (TED) can provide cooling for buildings and spaces with high cooling requirements as an alternative for traditional cooling and thus TED helps reduce in greenhouse gas (GHG) emissions. The effects of increased water temperature induced by TED on the drinking water quality and biofilm development within DWDSs are not yet known. Hence this thesis was initiated with the objective to investigate the effects of TED on microbial water quality and biofilm development within DWDSs. The first part of this thesis investigated the impacts of TED at 25 oC on microbiological drinking water quality, using pilot distribution systems. The first study revealed that the water temperature increased to 25°C in a pilot distribution system as a result of cold recovery does not affect the bacterial water quality in the drinking water phase. However, it does affect the concentration and community composition of biofilms (Chapter 2). Hence, in the second part of this thesis, the effect of TED on biofilm was investigated extensively. In pilot scale distribution systems, both water and biofilm phases were studied with water temperatures increased to 25 oC and 30 oC after TED. It was concluded that the timeline for biofilm microbial development was influenced by temperature: the higher the temperature, the faster the microbial development of a biofilm took place. Simultaneously, higher biomass activity (ATP and cell concentration) was also observed in the water phase. In the biofilm phase, the initial faster microbial development did not lead to differences in microbial diversity and composition at the end of the experimental period (Chapter 3). Similarly, biofilm development after TED at 25 oC followed for a long period of time, 99 weeks, showed that instantaneous increase in water temperature influenced the early stages of biofilm development. High temperature initiates faster growth of primary colonizers (Betaproteobacteriales, Sphingomonadaceae) (Chapter 4). Both studies univocally showed that as a result of constantly stable increased water temperature after TED, biofilms reached to a steady phase faster when compared to fluctuating drinking water temperatures in reference and control systems (Chapter 3 and 4). After studying the microbial water quality in unchlorinated drinking water distribution systems for both water and biofilm phases, initial investigation of TED application within chlorinated networks was also performed. Compared with unchlorinated DWDSs, here chlorine dramatically reduced the biofilm biomass growth, and raised the relative abundances of the chlorine-resistant genera (i.e. Pseudomonas and Sphingomonas) in bacterial communities. As a result of TED, no significant effects were observed on chlorine decay, microbial water quality and biofilm composition during the experimental period (Chapter 5). After extensively studying the changes in the microbial drinking water quality as a result of TED, the last part of this thesis was carried out to determine what raising the maximum temperature limit (Tmax) after recovery of cold would entail in terms of energy savings, GHG emission reduction and water temperature dynamics during water transport. A full-scale TED system was used as a benchmark, where Tmax is currently set at 15 °C. By raising Tmax to 20, 25 and 30 °C, the retrievable cooling energy and GHG emission reduction could be increased by 250, 425 and 600%, respectively. The drinking water temperature model predicted that within a distance of 4 km after TED, water temperature resembles that of the surrounding subsurface soil. Hence, a higher Tmax will substantially increase the TED potential of DWDSs while keeping the same comfort level at the customer’s tap (Chapter 6). All of these observations indicate that increasing Tmax up to 25-30 °C in TED can be safe in terms of microbiological drinking water quality. However, this is specifically the case for unchlorinated DWDSs with microbiologically stable water (AOC <10 ug C/L). More insight is required in terms of microbiological assessment of TED to further explore the potential within chlorinated systems. Further research on the effects of cold recovery on DWDSs already in operation is highly recommended. In order to get better insight on response of already developed biofilm towards increase in temperature after TED. Moreover, specific opportunistic pathogens that are sensitive to temperature increase, should be investigated thoroughly in order to provide hygienically safe water after recovery of cold from both chlorinated and unchlorinated drinking water distribution systems. @en