Kara L. Nelson

The Nelson research group aims to advance environmentally sustainable and socially equitable water infrastructure and practices around the globe.  We embrace the challenge of studying complex systems and recognize that engineering is only part of the solution.  We strive to bring attention and resources to understudied problems, leverage our unique capabilities as researchers at a world-class university while also recognizing our limitations, and collaborate with partners (academic and non-academic) with whom we have shared goals.  We aim to embody excellence in all that we do.  To support each other’s success, we actively work to cultivate an inclusive climate in the research group and to continuously educate ourselves about inclusive practices (e.g., many of us contributed to the development of ReNUWIt’s Inclusive Excellence Guides.)




WBE monitoring team

Our SARS-CoV-2 wastewater testing team.

Monitoring SARS-CoV-2 concentrations and strains in wastewater to inform an effective public health response  

Since the early days of the pandemic we have been developing methods to measure the concentration of SARS-CoV-2 in wastewater, and determine which strains are circulating. We operate a regional program to monitor COVID in the SF Bay Area. More details at www.covid-web.org and in this Berkeley News story.

Theme: WASH

Image charting sources and pathways of disease through humans, animals, and water

Erica graduated!

Pathways of Enteric Pathogen Transmission in Rural Bangladeshi Households  

Diarrheal illness is a leading cause of morbidity and mortality in low- and middle- income countries (LMICs). These illnesses result from the transmission of fecal pathogens, which are a concern in areas with inadequate sanitation facilities. Additionally, in LMICs there is often close proximity between livestock feces and human living areas due to the widespread practice of animal husbandry. Pathogens can be transmitted from human and animal feces to a new host through hands, soil, water, flies, and surfaces. Fortunately, proper sanitation practices can block the transmission cycle of these pathogens. Through my research, I investigate the transmission of enteric pathogens from human and animal sources in the context of a randomized controlled trial in rural Bangladesh, which focused on the impact of an improved sanitation intervention.


Image comparing a house with intermittent water supply on the left with house that has continuous water supply on the right

image:Complex biological, physical and chemical mechanisms can affect water quality during conveyance from source to consumer taps. Continuous positive pressure in piped distribution systems is an accepted standard for protecting drinking water from contamination. In continuous water supply (CWS), water supply is turned off or experience a loss of pipe pressure only during infrequent activities or emergencies. In contrast, the defining feature of IWS is regular interruptions of water conveyance and loss of water pressure. When supply is turned off in IWS systems, water drains through infrastructure deficiencies and consumer taps or collects at dead ends and low elevations, leaving pipes at low or less than atmospheric pressure while they are empty or there is stagnant water left between supply cycles. Between supply cycles, contamination can enter the distribution system as backflow or as intrusion. In addition, consumers with IWS are forced to store water which further increases the risk of contamination. Similar to CWS, microbial growth can also be found in IWS systems in bulk water, biofilm, and loose deposits.

Project Lead Karina: "I am working on data analysis and my dissertation."

Microbial Communities in Intermittent Water Supply

Intermittent water supply (IWS), defined as piped water supply that is available to consumers for less than 24 hour per day, is likely to remain a common practice due to the increase in access to piped water in low- and middle-income countries and the many factors that threaten drinking water resources and infrastructure. IWS has been shown to degrade microbial water quality and lead to around 4.52 million cases of diarrhea each year. However, there is limited knowledge on the influence of IWS on the diversity and dynamics of the IWS microbiome. IWS systems have unique and complex features that shape their microbiology, including low and negative pressures between supply cycles that can lead to intrusion and backflow and first flush events (when supply is restarted). Understanding how unique features of IWS impact water microbiomes can help better characterize risks of IWS and provide insight into strategies to protect water quality in IWS. Through my research, I investigate the effects of key features of IWS (i.e. drained periods, stagnation, and first flush events.) on drinking water microbial communities by integrating both field and laboratory approaches.  




Diagram showing a corroded distribution system pipe

Image: Microbial communities exist can be found in drinking water distribution systems in the biofilm, loose deposits, and bulk water phase. Within each phase, there is a range of different types of microorganism present.  This image illustrates the bacterial fraction of microorganisms in the bulk water phase of a drinking water distribution system pipe. It is important to understand how the microbial communities in these systems change as a result of major changes in water type or treatment- such as augmentation with advanced treated wastewater- so that adequate  microbial water quality can be ensured for consumers.

Project Lead Lauren "I am currently analyzing 16S rRNA gene sequencing data and prepping metagenomics reads for analysis."

Microbial Communities in drinking water distribution systems

Communities concerned about drinking water demands are realizing the potential in a sustainable resource that is largely discarded: wastewater. To utilize this resource safely and effectively, drinking water providers, engineers, and academics will need to implement advanced tools for microbial water quality assessment. However, the wastewater produced by a community alone is not enough to sustain a water supply. Instead, advanced treated wastewater will need to augment either traditional water sources through indirect potable reuse or conventionally treated drinking water through direct potable reuse (DPR). In DPR systems, blends of advanced treated water and conventional drinking water will be injected directly into drinking water distribution system (DWDS) pipes. Compared to indirect potable reuse systems, DPR systems will have no natural buffer for the advanced treated wastewater and may have lower ratios of conventional water in DWDSs. Advanced microbial water quality assessment techniques will help ensure that these systems are safe as compared to conventional drinking water systems. Furthermore, microbial water quality in conventional drinking water systems could improve with implementation of advanced assessment techniques. Research on methods of advanced microbial water quality assessment is needed for both conventional and DPR systems to diversify current microbial monitoring options and to make meaningful conclusions about the impacts of DPR systems on microbial water quality.

Impact of advanced wastewater treatment technologies on microbial abundance and communities at pilot- and demonstration-scale direct potable reuse facilities

Although there is growing recognition that the direct potable reuse (DPR) of water presents a safe option for diversifying water supplies, there are several key knowledge gaps regarding the impact of advanced treatment processes on biological water quality parameters the bacterial communities. DPR presents three unique microbiological risks to the DWDS microbiome and biostability. First, the composition of bacteria and organics in DPR source water (i.e. wastewater) differs considerably from conventional water sources (i.e. lake water, groundwater). DPR source water is dominated by human enteric microflora, whereas conventional source water microbiome consists primarily of environmental organisms. It is presently unknown if the human microflora present in DPR source water exerts an influence on the DWDS microbial communities. Second, DPR predominantly uses advanced treatment processes such as nanofiltration (NF), reverse osmosis (RO), and advanced oxidation processes (AOP, e.g. UV/H2O2) to massively suppress microbial numbers and remove contaminants of concern. However, these treatments render effluent waters biologically unstable when small molecular weight organics slip through membrane filtration or small numbers of bacteria persist into the DWDS. Survival of bacteria is partly due to compromised membranes, and regrowth occurs on bioavailable residual organics in the DWDS in the presence of a continuously degrading residual disinfectant.  Lastly, DPR likely will always involve blending with conventional water. Changes in blending ratios can induce bacterial community shifts, potentially resulting in a microbiome at risk of microbial regrowth and opportunistic pathogen proliferation.

Current understanding of the drinking water microbiome is inadequate to inform the design of DWDS to foster a stable, healthy drinking water microbiome and prevent proliferation of opportunistic pathogens and ARGs. Although this knowledge gap exists for conventional drinking water systems, it may represent a greater barrier for direct potable reuse (DPR), because it is a novel engineered system and will face greater scrutiny by experts, regulators, and the public. To build and maintain public confidence in DPR, new approaches are needed to understand how DPR advanced treatment systems impact microbial communities.  

Schematic of a pilot-scale direct potable reuse facility and bench-scale chlorination, reservoir, and simulated distribution systems

Image: Schematic of a pilot-scale direct potable reuse facility and bench-scale chlorination, reservoir, and simulated distribution systems.

Project lead Scott is nearing the end of PhD (anticipated graduation: December 2019), at which point he’ll have been a MS/PhD student for 6.5 years. Every PhD is very different - it is important for each PhD student to make their own story and craft their professional life in their own image. Projects are so long-term, and therefore there is SO much free time. Scott explored and took on many teaching and leadership positions along the way, and is grateful for the opportunities to do so





Image: Overview of the potential resource (N&P) path given source-separated urine is free of pathogens.

Project co-lead Soliver: "Previous experiments, highlighted the acid as the most costly component; consequently, I am currently optimizing experiments to increase fertilizer yield while decreasing acid quantities"

Project Co-lead Luis: " ... "

Presence and Inactivation of Enteric Viruses in Ammonium Fertilizer Derived from Source-Separated Urine via Cation Exchange

Source separation, the process of separating urine and feces at the toilet, is gaining attention for its potential to recover necessary macronutrients, and lower societal greenhouse-gas footprint and environmental pollution. Urine contains 80% of the total nitrogen load of wastewater streams, but constitutes only 1% of the total volume. Therefore, the extraction of nitrogen directly from urine could eliminate the need for nitrification and denitrification processes, and overall energy demand of conventional wastewater treatment. Additionally, this nitrogen, which can be extracted from source-separated urine via cation exchange and acidic elution, is readily available for plant uptake. However, the use of insufficiently treated urine in agriculture introduces a potential transmission route for waterborne pathogens, the cause of 3.4 million deaths (90% children)  annually. My research aims to preserve public health by (1) determining if these enteric viruses are persist through the fertilizer derivation process, and if they persist, (2) determine if there is potential for the inactivation of these pathogens by capitalizing on the virucidal and bactericidal properties of the acid and extracted ammonia to inactivate them. This research aims to reduce dependency on energy/cost intensive production/distribution of commercial nitrogen fertilizers, promote local agriculture, improve surface and groundwater quality, and ultimately public health.










Photolytic Oxidative Periphyton cell, Discovery Bay Treatment Wetlands Research Facility

Disinfection of Water by Sunlight

Sunlight is a powerful natural disinfectant, and yet there are still many knowledge gaps in understanding the fundamental mechanisms that lead to inactivation of microorganisms by sunlight.  Our research group studies both the direct and indirect sunlight-mediated processes that lead to inactivation of viruses and bacteria.  We also use our growing understanding of the fundamental mechanisms to evaluate the implications of sunlight disinfection in three important application areas: wastewater disinfection by natural treatment systems; solar disinfection of drinking water (SODIS); and beach water quality.  This work has been supported by the National Science Foundation, the Blum Center, and the International Water Management Institute.

Image: Photolytic Oxidative Periphyton cell, Discovery Bay Treatment Wetlands Research Facility


Boys collecting water from a submerged tap

Evaluation of 24x7 versus Intermittent Water Supply in Hubli-Dharwad, India and Arraijan, Panama

In many cities in the developing world, water is delivered through the piped network intermittently.  In Hubli-Dharwad, water arrives for a few hours every 2-5 days.   For the past several years, however, Hubli-Dharwad has been delivering water continuously, or "24x7", to 10% of the population through a World-Bank funded pilot project. We evaluated the water quality, health, and economic impacts of 24x7 water supply compared to intermittent water supply.  Currently, we are working in Arraijan, Panama, where the intermittency of water delivery is not as severe, but still poses a potential risk to water quality. This work has been supported by the National Science Foundation and the Blum Center, and the Inter-American Development Bank.

Image: Boys collecting water from a submerged tap


Former PhD student Gordon Williams at the pilot-scale flocculation tanks and dual media filters at the Monterey Regional Water Pollution Control Agency water reclamation plant

Tertiary Treatment for Non-Potable Water Reuse

Stringent regulations exist to ensure the safety of wastewater that is recycled for beneficial purposes in the United States.  To inform risk assessments, new treatment technologies and approaches must be evaluated.  Former PhD student Gordon Williams conducted research on the impact of loading rate on tertiary filtration of wastewater at a large pilot facility that we constructed at the Monterey Regional Water Pollution Control Agency.  As a result of his research, several full-scale treatment plants in California are now able to operate their tertiary filters at higher loading rates, which allows them to recycle more wastewater at minimal cost.  Another former student, Rabia Chaudhry, investigated the mechanisms of virus removal by membrane bioreactors (MBRs) and demonstrated that high removals of pathogenic viruses can occur due to attachment of viruses to mixed liquor solids, as well as rejection by the cake layer on a ripened membrane.  This project was part of the Tailored Water Theme at ReNUWIt.

Image: Former PhD student Gordon Williams at the pilot-scale flocculation tanks and dual media filters at the Monterey Regional Water Pollution Control Agency water reclamation plant


Urban farmer irrigating with wastewater in Accra, Ghana

Wastewater Irrigation of Food Crops

Unlike in the United States, the majority of wastewater in the developing world is discharged directly to the environment without any treatment.  Farmers downstream of cities often use the untreated wastewater for irrigation.  We are studying the health risks associated with this practice in Accra, Ghana as well as Hubli-Dharwad, India.  This work has been supported by the International Water Management Institute, the UCB Center for Emerging and Neglected Diseases, and the US EPA (through an EPA STAR Fellowship).

Image: Urban farmer irrigating with wastewater in Accra, Ghana



Stormwater Treatment by Bioinfiltration

Many cities have embraced stormwater management practices that involve increased capture of storm runoff by various types of bioinfiltration basins (e.g., rain gardens).  We are exploring the potential for different types of natural and geomedia, as well as more engineering operation of such basins, to remove and inactivate pathogens from stormwater before it is discharged to surface waters or infiltrates to recharge aquifers.  This project is part of the Stormwater Capture and Reuse Theme at ReNUWIt.  

Image: Demonstration bioinfiltration basins in El Cerrito, CA


Novel Disinfection Approaches

Our group works on development and evaluation of novel disinfection approaches, including nanoparticles of zero-valent iron (nZVI), iron oxide coatings, and quaternary ammonium silane (QAS) coatings.  These heterogeneous disinfection approaches require interactions between the disinfecting surface and the microorganism, and a major limitation is the presence of natural organic matter.  This work has been supported by the National Research Foundation of Korea (nZVI) and the Sustainable Products and Solutions Program (QAS and IOCS coatings).

Image: Inactivated E. coli cells on surface of QAS coated sand.


Mesita Azul household water treatment unit

Household Water Treatment and Safe Storage

Many households in the developing world only have access to drinking water sources that are at risk of microbiological contamination.  As a result, household water treatment and safe storage is promoted by many organizations, including the World Health Organization (WHO).  Our research group works on both the development and evaluation of point-of-use (POU) technologies as well as storage practices.  Technologies include the Mesita Azul (a UV Tube technology that was developed at UC Berkeley), SODIS, and QAS coatings.  We recently completed a 400-household evaluation of the Mesita Azul in Baja California Sur, which was implemented by the NGO Cantaro Azul (link).  We are an active member of the WHO's HWTS Network (link).  This work has been supported by the Blum Center and the Sustainable Products and Solutions Program.

Image: Mesita Azul household water treatment unit


Design drawing for pHreeLoo (pathogen free) disinfecting toilet prototype

Low-Cost Urban Sanitation and Resource Recovery

Our Safe Sludge research team developed an approach to disinfect human excreta in the toilet itself.  By killing pathogens first, all subsequent activities required for excreta management and resource recovery becomes safe.  The Safe Sludge process harnesses the natural disinfection power of the ammonia present in urine, simply by raising the pH.  This work was supported by the Bill and Melinda Gates Foundation.

Image: Design drawing for pHreeLoo (pathogen free) disinfecting toilet prototype


The Passive Latrine Use Monitor

Much effort is being invested in providing sanitation to the 2.6 billion people that still don't have access to improved sanitation.  However, just because a latrine is built does not mean that it will be used.  The Passive Latrine Use Monitor (PLUM) was developed by a team of Berkeley students, in collaboration with Prof. Tom Clasen at the London School of Hygiene and Tropical Medicine, to provide an objective measure of latrine use.  The information can be used to improve the understanding of sanitation behaviors and how to modify them, and for assessing the intended health, livelihood, and environmental benefits of improved sanitation.

Image: PLUM device installed in a latrine in Orissa, India