Due to the quick growth in human population and subsequently a high rate of urbanization, fresh water sources are under pressure. Estimated 1.8 billion people drink water from potentially sewage-contaminated sources and also the presence of antibiotic resistant bacteria in sewage has made the improper treatment of wastewater effluent an emerging problem. Iron electrocoagulation (Fe-EC) has shown to be successful in reducing pathogen concentration, although to different extent for types of pathogens. Besides, the water quality was found to be of influence on the effectiveness. This study therefore aimed to determine the removal mechanism for both bacteria and virus as well as assess the effect of wastewater components on the Fe-EC treatment process. EC experiments were conducted in an aerated beaker with a volume of 1L, continuously stirred. pH and current were kept stable at 7.5 and 200mA, respectively. The total charge dosage was 180 C/L. After electrolysis the samples were left to settle. Blank measurements were conducted in a 230 mg/L NaCl solution. Wastewater components were added in concentration of 4.0 mg/L for phosphate, 60 mg/L calcium, and 10 mg/L humic acids. E. coli WR1 and 휙X174 were used as indicator organisms. Contributing disinfection mechanisms for E. coli were inactivation and physical removal. During electrolysis a log removal of 3.8 log units was found, ascribed to inactivation. Further increase in removal to 6.0 log units was observed after settling. In the presence of TEMPOL only 0.3 log units removal were observed during electrolysis, but removal after settling still amounted 5.5 log units. For 휙X174 removal reactive species were not effective. Disinfection after settling equaled 4 log units, when settling was complete. Settling was found to be dependent on mixing conditions, and removal was correlated as well. Extended mixing promoted the formation of larger flocs and thereby enabled sweep flocculation for phage removal. Phosphate decreased attenuation of E. coli either for inactivation, 2.0 log units as for physical removal, 4.7 log units. Phosphate has high affinity for iron and competes with bacteria for iron surface. Calcium as well inhibited abatement of E. coli. Inactivation only amounted for 1.4 log units and removal after settling equaled 2.1 log units. Calcium is expected to complex bacteria surface, increasing repulsive forces between E. coli and iron. The effect of carbonate was only seen during electrolysis, 1.3 log units. The formation of the carbonate radical is suggested as explanation for the decrease in effectiveness. The effect of NOM on E. coli attenuation was unclear. Inactivation was inhibited to only 1.4 log units, but no effect was found on the total removal. Therefore, it can be concluded that NOM does not successfully compete with bacteria for iron surface. 휙X174 attenuation was not effected by addition of phosphate, calcium, or carbonate. On the other hand, the addition of NOM inhibited phage removal, only 0.6 log units in comparison to 4.0 log units for the blank. Adsorption of NOM onto iron surface is expected to negatively change the surface charge, inhibiting association between iron and virus.

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.

Tap water qualification is quite important for human health, the DNA extraction from tap water is a current challenge since the microbes inside is limited. This article aims to evaluate various DNA extraction methods and based on the different reagents or procedures and their influence to do some modifications for better extraction. DNA yield, purity and fragment size are three evaluation criteria for extracted DNA, while the reproducibility and operational convenience are also taken into evaluation for each method. According to the results, extraction methods could be recommended for different situations. It is concluded that commercial kits show better reproducibility in yield and quality aspects and more convenient in operation than phenol/chloroform based methods. The modified method which adds enzymatic and chemical lysis method into standard commercial kit protocol, shows the highest DNA yield. The phenol/chloroform based methods give the best average purity, especially for protein contaminants. Considering the fragment size, the DNA extracted from Quick-DNA HMW MagBead kit (ZYMO Research, USA) distributes widest with more HMW DNA among all methods. The results presented here suggest that that the DNA extraction method of choice for tap water samples should be the modified Quick-DNA HMW MagBead kit.

Drinking water safety is of great concern all around the world. Two strategies can be pursued to maintain biological stable drinking water during distribution in the network: (i) without a residual disinfectant, in which bacterial growth is controlled by very low biodegradable nutrients in the water by extensive pre-treatment and a well-maintained network and (ii) with a residual disinfectant in the water during distribution. Independent of the strategy, maintaining water quality during the transportation processes has always been a challenge, and there is a need for a better understanding of the impact of biological stability strategies using systematic studies. In this study, the impact of no residual disinfectant, residual chlorine and residual monochloramine on chemical and microbial water quality were investigated. It is anticipated that studies with pilot distribution networks will lead to better control of drinking water safety, in terms of biological stability and DBPs formation. Meanwhile, computer models applied in this study fitted disinfectant decay kinetics, and appeared to correspond with the experimental data for THMs and biofilm formation, and hence provided more insights in terms of predicting the behaviour of the system in the future, while their accuracy can also be calibrated and verified by the future experimental data.

Drinking water safety is critical to public health and the stability of drinking water quality is highly related with drinking water distribution systems (DWDSs). Antibiotic resistance genes (ARGs) and their hosts are the two major concerns in drinking water, however, the knowledge of fate of ARGs and their hosts were limited due to the current short-read length based sequencing technologies. Nanopore sequencing developed by Oxford Nanopore Technologies (ONT) is expected to overcome the challenges on ARGs and ARB characterization owing to its ultra-long reads generated. In this study, therefore, direct gDNA Nanopore sequencing was performed on treated water, distributed water and biofilm samples in two different DWDSs located at Kamerik and Lekkerkerk to explore its potential on ARGs and ARB characterization in drinking water systems. Additionally, the performances of taxonomy classification and ARGs profiling with Oxford Nanopore gDNA sequencing with different thresholds were assessed using an artificial microbial community. However, the conflict between the high requirements of input DNA quality and quantity with Nanopore sequencing and extremely low microbial biomass content in drinking water samples led to a challenge for our research. Therefore, evaluation on different sample preparation methods was conducted to meet the requirements of the input DNA.

With the growing population and economic development, there is more stress on natural water resources. Additionally, current and future water shortages, increasing environmental concerns and stringent discharge standards demand high-quality treated water. In this scenario, it is crucial to recover water and wastewater resources for reuse, reducing the dependency on new resources. While aiming for water reclamation, the influence of wastewater quality parameters on human health is given foremost attention in recent times. Enteric pathogens are a major concern when reclaiming municipal wastewater. Electrocoagulation (EC) process that introduces coagulants by electrochemical means has been successfully employed for the treatment of groundwater, industrial and municipal wastewater. EC has been widely accepted over other physicochemical processes due to its process design and lowcost material. In this research, EC has been thoroughly investigated as a tertiary treatment technology for water reclamation from municipal wastewater. This research is focused on determining the efficiency of low voltage iron EC for the removal of enteric pathogen indicators and antibiotic-resistant bacteria from secondary wastewater effluent. The effect of operational parameters: charge dosage (C/L) and charge dosage rate (C/L/min) on pollutant reduction was evaluated in different water matrices: demineralized water, synthetic wastewater effluent and real wastewater effluent. EC operated at 400 C/L, 7.2 C/L/min and natural pH allowed > 3.5 log units removal for E. coli and Enterococci, > 2.5 log units for ESBL E. coli and VRE and > 2 and 2.7 log units for Somatic coliphages and Clostridium perfringens spores respectively in real wastewater effluent. Furthermore, a significant reduction of phosphorous, COD and the true color was observed at 400 C/L and 36 C/L/min. Pollutant reduction was influenced by sedimentation and floatation mechanisms observed at varying charge dosage rates. A marginally higher removal rate constant of pathogen indicators as a function of charge dosage at low charge dosage rate showed slow iron dosing to improve microbial adsorption and increase contact time with iron precipitates. The reduction of pathogen indicators was associated with physical removal mechanisms like adsorption, sweep coagulation and entrapment within the flocs, charge neutralization and aggregation based on literature. The effective removal of physical, chemical and microbiological parameters in real wastewater effluent was achieved at 400 C/L and 7.2 C/L/min at an operating cost of 0.17 €/m3 indicating EC to be a cost-effective treatment in comparison to alternative technologies like ozone, UV, activated carbon and reverse osmosis.

Biological safety of drinking water is vital for safeguarding public health. Many efforts have been made to explore the microbial universe in drinking water. Nanopore sequencing developed by Oxford Nanopore Technologies is expected to enable PCR-free and rapid identification of species with high accuracy, thus overcoming the impediments of next-generation sequencing. However, the capability of Nanopore sequencing for characterizing the microbiome in drinking water with extremely low biomass content has not been explicitly evaluated. Therefore, this research was carried out to explore the potential of Nanopore sequencing for microbial community characterization and species identification in drinking water. In this study, NanoAmpli-Seq full-length 16S rRNA sequencing and 1D² genomic DNA (gDNA) sequencing were performed on an Oxford Nanopore MinION^TM sequencer. DNA samples of artificial microbial communities were sequenced in order to assess the performance of both sequencing strategies. Subsequently, DNA extracted from tap water was subjected to Nanopore sequencing with the two methods. Results showed that NanoAmpli-Seq 16S rRNA sequencing precisely identified abundant species in artificial microbial communities with high level of reproducibility but biased community profiles due to variation in PCR efficiencies of different species, whereas only 10 species were identified in tap water samples. In addition, raw results from 1D² gDNA sequencing provided an unbiased microbial community profile of an artificial community DNA, while polished data improved the species identification accuracy at the expense of the ability to profile the community structure. Furthermore, 45 hours’ sequencing generated more reliable results than 5 hours’ sequencing with higher profiling accuracy of community structure. Nevertheless, 1D² gDNA sequencing still did not exhibit desirable species identification performance on tap water DNA samples. Notably, despite two enteropathogenic species (Enterobacter cloacae and Laribacter hongkongensis) were identified, the detection of Homo sapiens in the same sample indicated the potential existence of post sample contamination. To conclude, Nanopore sequencing possesses great potential to serve as an efficient tool for study of drinking water microbiology. Specifically, notwithstanding the dissatisfactory performance of NanoAmpli-Seq, its high reproducibility across sequencing runs, adaptability to low DNA quality and quantity, and short turnaround time indicated its potential usefulness to promptly monitor microbial community changes subjected to environmental changes in extremely low-biomass samples (i.e. drinking water). Despite that 1D² gDNA sequencing exhibited superior performance on species identification and microbial community profiling to NanoAmpli-Seq, more endeavors should be made to overcome the hurdles (e.g. demand for high molecular weight gDNA, standard methods for analyzing sequencing data), thereby improving the species identification coverage and microbial community profiling accuracy in drinking water. Understanding the presence and dynamics of the microbial community in DWDS is important for water utilities to gain a better understanding of various microbial processes in drinking water from source to customers’ taps, based on which water treatment strategies could be improved and better management of drinking water quality could be performed.

The drinking water safety has been paid close attention, and the water purification development and distribution cleaning have been widely studied. To meet stricter water quality regulations and fight new emerging pollutants, upgrading treatment processes to improve treated water quality has become common practices worldwide. However, the quality improved drinking water still needs to be delivered by the old distribution system with harboured material which may cause serious water quality deterioration during the shifting of supply water quality. Until now, the accompanying transition effects within distribution networks caused by changes of water quality or hydraulic condition have been poorly documented. These irregular operations will impact water quality
negatively through the associated physiochemical and microbiological destabilization of accumulated materials such as loose deposits resuspension and biofilm detachment.
The destabilized materials would be released as suspended solids into bulk water and travel throughout distribution networks. Therefore, the investigation on changes of suspended solids characteristics is the key to understand transition effects. To study the transition effects through suspended solids, there are challenges: 1) suspended solids are diluted in the big volume of water, resulting in low concentration if take water samples; 2) the detection limit of regular parameters makes the changes hard to be noticed; 3) the
release of suspended particles is non-periodicity, which leads to the difficulty of catching the moment.
In my studies, the online particle sampling system (OPSS) was applied in three distribution systems to collect and monitor suspended solids, which successfully overcame all of the three challenges mentioned above. The main objective of this report is to study water quality changes under regular operations, and transition effects under irregular operations such as the upgraded treatment and pipe cleaning by using OPSS. At the end of the report, the problems were diagnosed and the management strategies were proposed for different systems.