Karl G Linden

University of Colorado Boulder | CUB · Department of Civil, Environmental and Architectural Engineering (CEAE)

UV light emitting diode (LED) disinfection technologies have advanced over the last decade and expanded the design space for applications in point of use, industrial, and now full-scale water treatment. This literature review examines the progression of UV LED technologies from 2007 to 2023 using key features such as total optical power, price, and...

A commercially available UVLED flow-through device, operating at 40 mJ/cm2, was examined for biofilm control on irrigation pipe material fed by wastewater effluent. Biofouling was monitored through total coliform counts, crystal violet (CV) staining, and ATP analyses. A UV fluence of 40 mJ/cm2 at 280 nm retarded biofilm formation; however, complete...

Crop irrigation with treated wastewater effluent using drip irrigation has become common as demand for water supplies has increased. Because of the quality characteristics of treated wastewater and the narrow...

Krypton chloride (KrCl*) excimer ultraviolet (UV) light may provide advantages for contaminant degradation compared to conventional low-pressure (LP) UV. Direct and indirect photolysis as well as UV/hydrogen peroxide-driven advanced oxidation (AOP) of two chemical contaminants were investigated in laboratory grade water (LGW) and treated secondary...

We present a study design and baseline results to establish the impact of interventions on peri-urban water access, security and quality in Kasai Oriental province of the Democratic Republic of the Congo. In standard development practice, program performance is tracked via monitoring and evaluation frameworks of varying sophistication and rigor. Mo...

Drinking water and sanitation services in high-income countries typically bring widespread health and other benefits to their populations. Yet gaps in this essential public health infrastructure persist, driven by structural inequalities, racism, poverty, housing instability, migration, climate change, insufficient continued investment, and poor pl...

The COVID-19 pandemic has promoted interest in using devices emitting ultraviolet-C (UVC) irradiation (200-280 nm) for surface disinfection to reduce pathogen transmission, especially in occupied public spaces. While UVC devices have been shown to be highly effective against various pathogens, there are safety concerns when using conventional UVC d...

Irradiation of nitrate (NO 3 ⁻ ) with UVC light below 240 nm generates photo-sensitized oxidants, such as hydroxyl radicals (•OH) and reactive nitrogen species (RNS). Hence, the combination UV/NO 3 ⁻ can be regarded...

Aerosols can transmit infectious diseases including SARS-CoV-2, influenza and norovirus. Flushed toilets emit aerosols that spread pathogens contained in feces, but little is known about the spatiotemporal evolution of these plumes or the velocity fields that transport them. Using laser light to illuminate ejected aerosols we quantify the kinematic...

Far UV‐C is an effective disinfection method that can be deployed in occupied areas. Commercially available krypton chloride (KrCl*) excimer lamps filtered to emit at 222 nm are effective in disinfecting pathogens and is safe for human exposure up to an allowable threshold exposure, which is much longer than for conventional UV lamps emitting at 25...

The applicability of chemical actinometry to characterize the fluence in UV reactors with reflections, non-parallel light, and variable water transmittance is limited due to the unknown effective path length or hydraulic shortcuts within the reactor. In this study, the effects of reflection and transmittance on actinometry were examined and a new,...

Reliable water service delivery continues to be a complex global issue that is particularly challenging in rural communities. Despite billions of dollars of infrastructure interventions, sustainable water services remain out of reach for millions of people. Professionalized maintenance services have emerged as a service provision strategy to supple...

This study maps and quantitatively analyzes the interaction of factors that drive (un)sustainable rural water service delivery in five regions across Ethiopia, Uganda, and Kenya by combining the knowledge and experience of 210 service delivery stakeholders, ranging from government officials, service providers and the private sector. We used semi-st...

Collaborative approaches can overcome fragmentation by fostering consensus and connecting stakeholders who prioritize similar activities. This makes them a promising approach for complex, systemic problems such as lack of reliable, safe water, sanitation, and hygiene (WASH) services in low-income countries. Despite the touted ability of collaborati...

Abstract Germicidal ultraviolet (UV) devices have been widely used for pathogen disinfection in water, air, and on food and surfaces. Emerging UV technologies, like the krypton chloride (KrCl*) excimer emitting at 222 nm, are rapidly gaining popularity due to their minimal adverse health effects compared to conventional UV lamps emitting at 254 nm,...

The emergence of COVID-19 and corresponding public health burden has prompted industries to rapidly implement traditional and novel control strategies to mitigate the likelihood of SARS-CoV-2 transmission, generating a surge of interest and application of ultraviolet germicidal irradiation (UVGI) sources as disinfection systems. With this increased...

Bench‐scale testing was conducted to evaluate the application of an Ultraviolet‐hydrogen peroxide (UV‐H2O2) advanced oxidation process (AOP) for the destruction of 1,4‐Dioxane (47 μg/L) and varying concentrations of three volatile organic chemicals (VOCs), including trichloroethylene (TCE), tetrachloroethylene (PCE), and 1,1‐dichloroethylene (1,1‐D...

Far UV-C, informally defined as electromagnetic radiation with wavelengths between 200 and 230 nm, has characteristics that are well-suited to control of airborne pathogens. Specifically, Far UV-C has been shown to be highly effective for inactivation of airborne pathogens; yet this same radiation has minimal potential to cause damage to human skin...

While preventive maintenance services have emerged as promising interventions to improve the continuity of water service delivery, the operational and contextual requirements for sustained functionality within maintenance models are not well understood. This paper uses data analysis to better understand factors influencing the success of rural wate...

This study sought to coalesce sector knowledge on the use of systems approaches for sustainable water, sanitation, and hygiene (WASH) service delivery in low-income countries. To accomplish this objective, we remotely convened a panel of WASH sector experts within a multiround survey to identify, characterize, and prioritize the necessary attribute...

Adenoviruses are known to be one of the most resistant viruses to UV disinfection. This study determined the inactivation kinetics of adenovirus freshly isolated from sewage samples, and compared the results with reference adenovirus stocks grown in the laboratory. Human adenoviruses were isolated from sewage sample using the HEK 293 cell line. Ina...

Opportunistic pathogens (OPs), such as Pseudomonas spp., Legionella spp., and mycobacteria, have been detected in biofilms in drinking water distribution systems and water storage tanks and pose potential risks to finished drinking water quality and safety. Emerging UV technologies, such as UV light emitting diodes (LEDs) and krypton chloride (KrCl...

Professionalized maintenance arrangements are emerging and growing to improve rural water service sustainability across sub-Saharan Africa, where local governments often act as rural service authorities. Uganda’s Ministry of Water and Environment released a novel policy in 2019 to promote professionalization, outlining requirements of local governm...

Decentralization in many African countries makes local governments responsible for water, sanitation, and hygiene (WASH) service provision. Yet service provision is complex and requires concerted inputs from many actors, thus local governments are increasingly collaborating with internal and external stakeholders. These ‘collaborative approaches’,...

Despite decades of global development programming, poverty persists in the low-and-middle-income countries targeted by these efforts. Training approaches to global development must change and the role of engineers in these efforts must evolve to account for structural and systemic barriers to global poverty reduction. Rapid growth in Global Enginee...

Systems for regular, preventive maintenance of infrastructure are needed to ensure safe water access globally. Emerging and growing across rural sub-Saharan Africa, professionalized maintenance arrangements feature legal, regulated service providers who maintain infrastructure in exchange for consumer payment through contracts. However, little is u...

Concern over water scarcity is turning global attention towards reclaiming wastewater to fulfill unmet water demands. Innovative water treatment solutions, like UV LEDs, can be applied in novel ways to...

This study investigated the benefits of using in-situ ozonation to extend ceramic membrane filtration and mitigate fouling during treatment for wastewater reuse. Pre-ozonation has been proven to diminish ceramic membrane...

While organisations across the world struggle to extend access to the 522 million living in rural areas without clean water, those who do have access do not necessarily use it. This paper explores why, within areas that have public taps with treated water, some individuals continue to use water from untreated sources. We focus on non-use of availab...

Effective disinfection technology to combat severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can help reduce viral transmissions during the on-going COVID-19 global pandemic and in the future. Ultraviolet (UV) devices emitting UVC irradiation (200-280 nm) have proven to be effective for virus disinfection, but limited information is ava...

Mid-tech water and sanitation infrastructure – interventions that make moderate use of resources, materials, and technology while providing improvements in health and well-being – may serve an important intermediate role for communities that cannot immediately get high-tech piped infrastructure. However, such systems must be socially appropriate, t...

Collaborative approaches are seen as a promising way to strengthen Water, Sanitation, and Hygiene (WASH) service delivery systems when challenges exceed the mandates and capabilities of any single entity. While collaborative approaches are well studied in high-income country contexts, current understanding of their application to international deve...

Even as progress has been made in extending access to safe water and sanitation under the Sustainable Development Goals (SDGs), substantial disparities in water, sanitation, and hygiene (WASH) services persist in high-income countries around the world. These gaps in service occur disproportionately among historically marginalized, rural, informal,...

Global engineers must be taught to consider the historical and present causes of persistent poverty and systemic barriers to prosperity. Such training will better inform the choices engineers make and help move the engineering sector away from a product and community-level focus towards working to address the root causes of poverty. A framing for G...

Almost half of the world’s population is living without access to sanitation services that are safe, reliable, and minimize public health risk of human waste exposure. Modern flush-based sanitation networks are unsustainable: substantial resources, namely water and fuel, are required to bring human waste to centralized treatment facilities. Moving...

Ultraviolet (UV) devices emitting UVC irradiation (200–280 nm) have proven to be effective for virus disinfection, especially on surfaces and in air, due to their rapid effectiveness and limited to no material corrosion. Numerous studies of UV-induced inactivation focused on nonenveloped viruses. Little is known about UVC action on enveloped viruse...

This research assessed the efficacy of UV and UV advanced oxidation processes (UV/AOPs) to reduce dissolved organic carbon (DOC), total petroleum hydrocarbons (TPH), and microorganisms in hydraulic fracturing produced water. To improve water quality conditions before UV treatment with and without added hydrogen peroxide (UV/H2O2), produced water wa...

Reuse of hydraulic fracturing wastewaters depends on effective tailored treatment to prepare the water for the intended end use. Aerobic biological treatment of hydraulic fracturing produced water was examined to degrade dissolved organic carbon (DOC) and polyethylene glycols (PEGs). Biological treatment experiments of three produced water samples...

Household water, sanitation and hygiene (WASH) practices in remote, rural, and unpiped communities are likely to impact exposure to pathogens beyond the fecal-oral transmission routes that are typically prioritized in WASH interventions. We studied 43 homes in two remote, rural, unpiped communities in Alaska to evaluate seasonal water haul, water s...

To address the complex challenge of sustaining basic water and sanitation services in low income settings, international organizations and local and national government entities are beginning to design and implement interventions explicitly aimed at addressing system weaknesses. Often referred to as “systems approaches,” these interventions seek to...

Group model building (GMB) approaches have been shown to improve participants' understanding of complexity by shifting and aligning individuals' mental models of the interconnections within complex systems. However, reviews of GMB literature have identified knowledge gaps for assessing the efficacy of GMB activities. To address these gaps, these st...

This research presents 56 experiments on hydraulic fracturing flowback and produced waters to evaluate common factors affecting electrocoagulation (EC) removal of turbidity, chemical oxygen demand (COD), dissolved organic carbon (DOC) and final pH. Additionally, qualitative reductions in the common fluid additives polyethylene glycols (PEGs) and po...

This work describes the development of a solid-phase extraction method capable of detecting common fracturing fluid additives in flowback and produced water with mass spectrometry. Dissolved organic carbon (DOC) was used as a bulk measurement to investigate the retentive capacity of seven sorbents and to determine a loading volume. Conductivity was...

Drought-driven humanitarian emergencies are becoming more frequent in the Horn of Africa where millions of people in this arid region face chronic water and food insecurity. Evidence from the region shows increasing reliance on groundwater supplies, infrastructure and institutional systems in response to decreasing rainfall. Drought emergencies can...

The international development sector is increasingly implementing collaborative approaches that facilitate a range of sectoral-level stakeholders to jointly address complex problems facing sustainable public service delivery, for which guidance does not explicitly exist. The literature on collaborative approaches has been built on experiences in hi...

Nitrate is ubiquitous in natural and human impacted water systems. Irradiation of nitrate by UV light during water treatment can produce hydroxyl and other radicals (e.g., reactive nitrogen species) that react with and oxidize organic contaminants. The aim of this study was to investigate water quality and operational conditions that impact radical...

Rural water supply services worldwide consistently fail to deliver full public health impacts as intended due to a low service sustainability. This failure is increasingly attributed to weak local systems composed of social, financial and environmental factors. Current approaches in the water, sanitation and hygiene (WASH) sector for understanding...

Endemic issues of sustainability in the water, sanitation, and hygiene (WASH) sector have led to the rapid expansion of ‘system approaches’ for assessing the multitude of interconnected factors that affect WASH outcomes. However, the sector lacks a systematic analysis and characterization of the knowledge base for systems approaches, in particular...

An environmental water sample fractionation framework was developed based on effects-directed analysis (EDA) to detect known and unknown compounds of concern in different waters. Secondary effluent from a wastewater treatment plant was used to demonstrate the effectiveness of the developed framework for characterizing estrogenic compounds in the ef...

Absorbance- and fluorescence-based optical parameters are commonly used as surrogates in engineered systems, but there is no systematic approach for selecting robust parameters. This study develops a methodology that is applied to a case study of differentiating wastewater effluent organic matter from naturally-derived organic matter. The methodolo...

Microbial safety of drinking water is of utmost importance for health. In many regions of the world, water shortage leads to direct or indirect reuse of wastewater or use of other unsafe water sources. Quantitative Microbial Risk Assessment (QMRA) can be used to determine which combination of water treatment processes is needed to provide safe wate...

Public health interventions targeting contaminated drinking water and indoor air pollution may help to reduce two of the leading causes of death among children under 5 in Rwanda - diarrhea and pneumonia. These interventions also have the potential to provide economic benefits, including reduction in expenditures on fuelwood and time spent on fuelwo...

Ultraviolet light emitting diodes (UV LEDs) have increasing applications in the inactivation of microorganisms in water, air, food, and on surfaces. System designers currently have metrics for comparison of the microbial and energy efficiency of UV LEDs, but these have not included a time component. Without including the time efficiency of a UV LED...

Standard protocols for the measurement of irradiance, peak wavelength, and emission spectra have not yet been established for UV LED devices. This lack of standardization creates an uneven field for comparison between products. A detailed protocol was developed and tested in fourteen facilities spanning manufacturers of UV LEDs and devices and rese...

Rainwater collection is a common source of household water in developed and developing communities where treated on-site water is not available. Although rainwater catchment has been practiced for generations in rural Alaska communities, there is little data available on the quality and quantity of rainwater resources. Forty-eight rainwater samples...

This study analyzed combinations of conditions that influence regular payments for water service in resource-limited communities. To do so, the study investigated 16 communities participating in a new preventive maintenance program in the Kamuli District of Uganda under a public–private partnership framework. First, this study identified conditions...

Disinfection by ultraviolet (UV) light via non‐mercury light‐emitting diodes (LEDs) may be a sustainable solution for drinking water disinfection in small systems. The world's first commercial UVC LED water disinfection reactor (the PearlAqua by Aquisense) was studied over a year‐long demonstration test, and performance was compared side by side wi...

The efficacy of germicidal ultraviolet (UV-C) light emitting diodes (LEDs) was evaluated for inactivating human enteroviruses included on the United States Environmental Protection Agency (EPA)’s Contaminant Candidate List (CCL). A UV-C LED device, emitting at peaks of 260 nm and 280 nm and the combination of 260/280 nm together, was used to measur...

This work critically evaluates the current paradigm of water distribution system management and juxtaposes that with the potential benefits of employing UV irradiation, which we hope will catalyze a judicial re-evaluation of the current practices in water distribution system management and spur critical research and a new way of thinking about seco...

Water and sanitation service delivery is complex and cannot be sustained by any one single actor. Recognising this prompts the need for approaches that integrate the diverse perspectives of the many actors involved in delivering services, align incentives, and strengthen collaboration. Countless methods and models for collaborative, action-based ap...

UV-based advanced oxidation processes (AOPs) have been widely explored to remove organic contaminants from water streams. In this lab-scale study, the removal of 17 trace organic chemicals (TOrCs) by UV/H2O2, UV/PDS and UV/Chlorine was investigated at equimolar radical promoter concentrations in municipal wastewater. Direct comparison of the UV-AOP...