Multiple treatment objectives of solar driven electrolytic oxidant production for decentralized water treatment in developing regions and its economic feasibility

Im Jahr 2017 konsumierten knapp 2 Milliarden Menschen fäkalkontaminiertes Wasser. Das führte zu fast 500.000 Todesfällen. Gleichzeitig werden Trinkwasserressourcen ausgebeutet und schon heute sind 4 Milliarden Menschen von Wasserknappheit betroffen. In ländlichen Entwicklungsregionen stellt, aus technischer Sicht, die Desinfektion des Wassers eine der größten Herausforderungen für die Sicherstellung einer angemessenen Trinkwasserversorgung dar. In dieser Dissertation wird die technische sowie wirtschaftliche Machbarkeit einer solar betriebenen Anlage zur Chlorproduktion mittels Inlineelektrolyse (ECl2) als Alternative zur Lieferung und Dosierung von Chlorreagenzien analysiert und bewertet. Während der ECl2 wird das gesamte aufzubereitende Wasser durch eine Elektrolysezelle geleitet und das Chlor aus dem natürlichen Chloridgehalt des Wassers „inline“ gebildet. Unter opti-malen Betriebsbedingungen kann Trinkwasser aber auch aufbereitetes Abwasser ohne Zugabe durch Chemikalien desinfiziert werden. Damit würde die Lieferung von Chlorlösung dauerhaft entfallen. Zusätzlich wurde bewertet, inwiefern die Entfernung von Eisen und Arsen durch die ECl2 sowie der Abbau von organischen Spurenstoffen durch zusätzliche Kombination mit UV-Bestrahlung zur Radikalbildung verbessert werden kann. Alle vorgestellten Feldtests wurden in Langzeitstudien unter Realbedingungen in zukünftigen Anwendungsgebieten durchgeführt. Dadurch konnten mögliche Probleme im Be-trieb der Anlagen frühzeitig erkannt und Lösungsvorschläge erarbeitet werden. Die Erfahrungen aus dem Betrieb der ECl2-Systeme stellen dabei den größten Nutzen dieser Arbeit dar. Mit den Feldversuchen konnte gezeigt werden, dass Wasser durch die Anwendung von ECl2 sicher desinfiziert und gleichzeitig ausreichend vor Wiederverkeimung geschützt werden kann. Insbesondere die Kombination mit naturnahen Verfahren zur Vorbehandlung des zu desinfizierenden Wassers hat sich als sehr vorteilhaft für die langfristig sichere Anwendung des Verfahrens herausgestellt. Für den in Uttarakhand, Indien, durch-geführten Feldtest konnte die ECl2 zusammen mit der Uferfiltration eine Logstufenreduktion von > 5.0 für Gesamtcoliforme und 3.5 für E. coli erreichen. Durch die Kombination mit einer vertikal durchströmten Pflanzenkläranlage (VFCW) konnte die Desinfektion von behandeltem Abwasser mittels Chlor erheblich vereinfacht werden. Die Pflanzenkläranlage reduzierte die Ammoniumkonzentration, den CSB sowie die Trübung und damit auch die Chlorzehrung des Wassers. Darüber hinaus wurden durch die VFCW Konzentrationsschwankungen im Zulauf erheblich vergleichmäßigt. Es wurden Logstufenreduktionen für Gesamtcoliforme von 5.1 und >4.0 für E. coli erzielt. Durch diese Verfahrenskombination werden auch Anwendungen zur Wiederverwendung von Abwasser möglich, die über die Bewässerung hinausgehen und damit wertvolle Frischwasserressourcen geschont. Durch die Behandlung von arsenkontaminiertem Grundwasser konnten mit der hier vor-geschlagenen Kombination von ECl2 und anschließender gemeinsamer Ausfällung und Filtration Entfernungsraten für Arsen von 94 % und Eisen von > 99 % erreicht werden. Da der WHO-Grenzwert für Arsen (10 µg/L) im hier durchgeführten Feldversuch mit 10 ± 4 µg/L dauerhaft nicht sicher eingehalten werden konnte, wurden weitere Optimierungsschritte identifiziert. Die Entfernungsrate für Benzotriazol von 5 % durch ECl2 allein konnte in Kombination mit UV-Lampen auf 89 % erhöht werden. Ähnliche Ergebnisse wurden für andere aus-gewählte organische Spurenstoffe erzielt. Es sind jedoch weitere Studien erforderlich, um den Abbauprozess im Detail zu verstehen und eine mögliche Zunahme der Toxizität durch die Bildung von Transformationsprodukten sowie Desinfektionsnebenprodukten zu bewerten. Die Feldversuche haben gezeigt, dass ECl2 als innovative Behandlungstechnologie in der Lage ist, Trinkwasser und behandeltes Abwasser sicher zu desinfizieren. Darüber kann mittels ECl2 u.a. die Entfernung von Arsen aus verunreinigten Rohwässern als auch der Abbau von Spurenstoffen verbessert werden. Bei härterem Rohwasser steht die rasche Verkalkung der Kathoden jedoch einem wartungsarmen Betrieb der Anlagen, trotz Polumkehr, entgegen. Die Versuche haben ge-zeigt, dass ECl2-Systeme mit den hier verwendeten Elektrolysezellen, nur in Wässern mit einem Gesamthärtewert 200 mg/L aufweisen, ist der Anwendungsbereich der ECl2 begrenzt und erfordert alternative Chlorierungstechnologien zur ursprünglich geplanten Inline-Elektrolyse. Bereits während Versuchen zur Abwasserdesinfektion in Spanien wurde daher das Pilotsystem technisch dahingehend angepasst, dass nur noch ein Teilstrom von 4 bis 23 % des zu behandelten Wasservolumens durch die Elektrode floss. Dadurch konnte die Bildung von Ablagerungen vollständig verhindert und ein zuverlässiger, nahezu wartungsfreier Betrieb sichergestellt werden. Je nach dem Chlorbedarf und der natürlichen Chloridkonzentration des Wassers erfordert diese Betriebsweise in der Regel jedoch die Zugabe von Chlorid. In Anbetracht der hier ermittelten erhöhten Prozessstabilität und dem erheblich reduzierten Energieverbrauch erscheint diese Zugabe vertretbar. Laborstudien haben auch gezeigt, dass die Bildung anorganischer Desinfektionsnebenprodukte bei den „onsite chlorine generation“ (OCG) Systemen kein Problem darstellt. Um die wirtschaftliche Machbarkeit der hier getesteten Trinkwasseraufbereitungssysteme unter Realbedingungen zu bewerten, wurden der Betrieb eines in Ägypten eingesetzten ECl2-Aufbereitungssystems und zweier in Tansania und Nepal eingesetzter OCG-Einheiten analysiert. Die Studie zeigt, dass die Betriebs- und Wartungskosten solcher Einheiten dauerhaft gedeckt werden können. Für den Aufbau der Infrastruktur sind jedoch Investitionen durch entsprechende Förderprogramme erforderlich. Die hier angewandten Verfahren zur Wasseraufbereitung können eine wichtige Rolle bei der Verbesserung der Trinkwasserversorgung insbesondere in ländlichen Entwicklungsregionen und der Wiederverwendung von aufbereiteten Abwässern spielen.In 2017 nearly 2 billion people consumed water that was contaminated with feces, causing almost 500.000 diarrheal deaths. At the same time freshwater resources are depleted and water scarcity is already affecting 4 billion people worldwide. From a technical perspective the continuous supply of chemicals needed to ensure sufficient disinfection remains a major challenge in rural water treatment, and existing technical solutions to adequately disinfect water have failed in the past. This dissertation work evaluates the technical and economic feasibility of solar-driven inline electrolytic production of chlorine (ECl2), as an alternative to external chlorine supply. During ECl2 disinfection the water passes through the cell and chlorine is produced “inline” from the natural chloride content of the water. Under optimal conditions, no chemicals are required to safely disinfect drinking water and treated wastewater. Fur-thermore, the ability of ECl2 to enhance the removal of iron and arsenic from contaminated groundwater and to degrade Trace Organic Compounds (TOrC) when combined with UV were analyzed. All relevant tests have been conducted in long-term field studies in future deployment areas. This enabled the evaluation of potential operational challenges of such systems under real-world conditions. The experiences gathered from these field trials represent the major benefit of this dissertation work. The trials have shown that with ECl2 water can be safely disinfected and supplied with an adequate amount of residual disinfectant. Here, the combination with natural pre-treatment systems has proven to be beneficial. For the drinking water trial conducted in Uttarakhand, India, the ECl2 system received bank filtrate and achieved overall log re-moval rates of >5.0 for total coliforms and >3.5 for E. coli. For the disinfection of treated wastewater, the combination with a vertical flow constructed wetland (VFCW) has largely simplified the disinfection with chlorine by equalizing wastewater (WW) inlet quality fluctuations, removing ammonium, COD, and turbidity. This has also substantially reduced the chlorine demand of the water, and pathogen indicator-free conditions were achieved with log unit removals of 5.1 and ≥ 4.0 for total coliforms and E. coli, respectively. Wastewater reuse applications that go beyond irrigation become permissible through this approach and the use of limited freshwater resources can be substituted. Removal rates for arsenic and iron of 94 % and >99 % respectively were able to be achieved by treating contaminated groundwater with the combination of ECl2 and subsequent co-precipitation and filtration proposed here. Despite effluent concentrations up to 10 ± 4 µg/L for arsenic, strict WHO guideline values could not be met. Here further optimization requirements were identified. The removal rate for benzotriazole of 5% through ECl2 alone could be increased to 89 % when combined with UV lamps. Similar results were achieved for other selected TOrCs. Still, more advanced studies are required to understand the degradation process in detail, and to evaluate a potential increase in toxicity through the formation of transformation products. The field trials have shown that ECl2 as an innovative treatment technology is capable of safely disinfecting drinking water and treated wastewater. Its application also enhances the treatment of other contaminants evaluated. However, cathode scaling has been iden-tified as the most critical technical issue - despite the use of polarity inversion. ECl2 systems could only operate reliably in waters with total hardness value < 200 mg/L CaCO3. As such concentrations are rare, the fields of application of ECl2 are limited. This required other chlorination technologies as alternatives to the originally planned inline electrolysis. An initial derivative of an ECl2 system was also applied during a wastewater disinfection trial in Spain. In this setting the portion of water passing by the electrodes and therefore the quantities of scaling agents were reduced to between 4 and 23 % of the total water volume treated. With this approach, deposit formation was completely prevented and reliable, nearly maintenance-free operation was ensured. However, such onsite chlorine generation (OCG) units commonly require the addition of chloride. From the author’s perspective and the experience collected during the field trials, the addition of NaCl is justifiable considering the increased reliability of system operation. OCG offers further advantages regarding process stability and energy demand. Lab studies have also shown that the formation of inorganic disinfection byproducts has not been an issue with OCG systems. To evaluate the economic feasibility of the drinking water treatment systems tested in real-world scenarios, an ECl2 treatment system operating in Egypt and two OCG units operating in Tanzania and Nepal were analyzed. The study shows that long-term operation and maintenance costs of such units can be covered. However, seed investment is required for the construction of the initial infrastructure. Once those costs are covered, the treatment approaches presented here can sustainably play an important role in reducing the number of people consuming contaminated water, especially in rural developing regions

Chlorination as Drinking Water Disinfection Technique and Disinfection by Products: A Scientometric Analysis

The Sustainable Development Goals (SDG) 2015, defined to achieve a better and more sustainable future, contains goal number 6 related to safe and affordable drinking water facility for all till 2030. The rural and remote areas in the developing countries predominantly face the scarcity of pathogen free drinking water leading to water borne diseases and deaths due to consumption of contaminated water indicating a need of advancement in the drinking water disinfection techniques. The paper discusses scientometric analysis of publication trends in chlorination as a popular disinfection techniques and research related to the Disinfection By Products (DBPs) that are produced due to the reaction between the disinfectant and naturally occurring organic matter in water. The analysis of the existing SCOPUS database from year 2000 to 2020, indicates total of 1279 journal articles, 138 conference proceedings, 88 review papers, and 57 other documents, with the key words ‘drinking water, disinfection, and chlorination’. As per the analysis, United States and China presented maximum publications related to drinking water disinfection using chlorination treatment. The analysis of literature also indicates that there is huge amount of literature related to the formation of alternative DBPs and their hazardous effects on human health. However, as per scopus database only three research documents are registered till date for the removal techniques of DBPs produced after the disinfection process, indicating a need of further research in this area. The literature also suggests the need to engender new technology or optimize the existing technology for minimizing the formation of DBPs

Removal of fluoride and pathogens from water using the combined electrocoagulation-inline-electrolytic disinfection process

This research article was published in Water Supply Journal, Volume 23, Issue 7, 2023The consecutive removal of fluoride (defluoridation) and pathogens (disinfection) in drinking water through combined electrocoagulation-inline-electrolytic disinfection (EC–ECl2) process with aluminum and dimension-stable mixed oxide electrodes was reported in this study. Laboratory trials were conducted on the effects of flow rate, initial pH, current density, and supporting electrolytes for defluoridation and disinfection processes. The results have shown that with a flow rate of 10 L/h, initial pH of 6, the current density of 9.4 mA/cm2 (EC cell) and 3.1 mA/cm2 (ECl2 cell), supporting electrolyte concentration of 165 mg/L, and electrolysis time of 50 min, a defluoridation rate of 88% (initial concentration of 12.3 mg/L) and complete disinfection (initial fecal coliforms of 19,700 colony-forming units per 100 mL (CFU/100 mL)) can be reached. The final concentration of fluoride and pathogens in treated water was 1.44 mg/L and 0 CFU/100 mL, which are within the acceptable limit of the World Health Organization and the Tanzania Bureau of Standards of 1.5 mg/L and 0 CFU/100 mL, respectively. The EC–ECl2 system is a promising approach for consecutive defluoridation and disinfection of water to save millions from fluorosis and waterborne diseases. However, optimization potential with regard to energetic efficiency and system complexity was identified

Oxidation of Selected Trace Organic Compounds through the Combination of Inline Electro-Chlorination with UV Radiation (UV/ECl2) as Alternative AOP for Decentralized Drinking Water Treatment

A large variety of Advanced Oxidation Processes (AOPs) to degrade trace organic compounds during water treatment have been studied on a lab scale in the past. This paper presents the combination of inline electrolytic chlorine generation (ECl2) with low pressure UV reactors (UV/ECl2) in order to allow the operation of a chlorine-based AOP without the need for any chlorine dosing. Lab studies showed that from a Free Available Chlorine (FAC) concentration range between 1 and 18 mg/L produced by ECl2 up to 84% can be photolyzed to form, among others, hydroxyl radicals (OH) with an UV energy input of 0.48 kWh/m3. This ratio could be increased to 97% by doubling the UV energy input to 0.96 kWh/m3 and was constant throughout the tested FAC range. Also the achieved radical yield of 64% did not change along the given FAC concentration range and no dependence between pH 6 and pH 8 could be found, largely simplifying the operation of a pilot scale system in drinking water treatment. Whereas with ECl2 alone only 5% of benzotriazoles could be degraded, the combination with UV improved the degradation to 89%. Similar results were achieved for 4-methylbenzotriazole, 5-methylbenzotriazole and iomeprol. Oxipurinol and gabapentin were readily degraded by ECl2 alone. The trihalomethanes values were maintained below the Germany drinking water standard of 50 &micro;g/L, provided residual chlorine concentrations are kept within the permissible limits. The here presented treatment approach is promising for decentralized treatment application but requires further optimization in order to reduce its energy requirements

The AquaNES Project: Coupling Riverbank Filtration and Ultrafiltration in Drinking Water Treatment

Natural water treatment techniques combined with engineered solutions were investigated at demonstration sites in Europe within the AquaNES project. Ultrafiltration is well-established in water treatment, but is not feasible for many water utilities due to its high operational costs compared to conventional treatment. These differences in cost are caused by membrane fouling and the associated cleaning required. This study aims to assess the economic and energetic operation factors based on studies of an out/in ultrafiltration treatment plant for river water and bank filtrate. The fouling potential of both raw water sources was investigated as well as the quality of the resulting water. In addition, the results show the potential utility of a combined approach utilizing bank filtration followed by ultrafiltration in drinking water treatment. In a separate consideration of the treatment process, the water quality does not fulfill the requirements of the German drinking water ordinance. A new method for the removal of dissolved manganese from the bank filtrate is presented by inline electrolysis. While this improves water quality, this also has a significant influence on fouling potential and, thus, on operating costs of ultrafiltration. These aspects lead to a fundamental decision for operators to choose between more costly ultrafiltration with enhanced microbiological safety compared to cost-effective but less stringent drinking water treatment via open filtration

Solar-powered drinking water purification in the oases of Egypt\u27s Western Desert

© The Authors. Published by SPIE under a Creative Commons Attribution 4.0 Unported License. We focus on the potential of using solar PV powered, decentralized drinking water treatment technologies for providing communities in remote areas with safe drinking water. Small-scale, solar PV-powered solutions for water purification may help achieve the sustainable development goals in areas without electricity access. However, more field-based research on the performance of solar-powered drinking water technologies is needed in order to perfect existing technologies. We introduce the first longer-term applied field study on the performance of 16 solar PV-powered drinking water stations using greensand filters for iron removal and anodic oxidation for chlorine production in the oases across Egypt\u27s Western Desert. Local groundwater shows natural iron concentrations that in some places exceed the WHO standard (0.3 mg/l) by a factor of 50. The presented results show that the energy efficient, solar PV-operated stations successfully remove the iron from the water. Chlorine levels vary by location and are connected to local consumption patterns and site-specific system settings. Simple adjustments are needed in order to fully benefit from the solar-driven anodic oxidation process. Solar-powered technologies for drinking water purification need to be able to respond to specific local conditions in order to become an upscalable solution for remote, rural areas across the globe

High-speed PIV applied to the wake of the NASA CRM model in ETW at high Re-number stall conditions for sub- and transonic speeds

Within the framework of the EU project ESWIRP the Particle Image Velocimetry (PIV) using high-speed camera and laser has been used to measure the turbulent flow in the wake of a stalled aircraft wing. The measurements took place on the Common Research Model (CRM) provided by NASA in the pressurized cryogenic European Transonic Wind tunnel (ETW). A specific cryo-PIV system has been used and adapted for using high-speed PIV components under the cryogenic conditions of the wind tunnel facility. First results are presented comprising transonic and subsonic stall conditions at realistic flight Reynolds numbers of 11.6 and 30 million, respectively