Menu Leddy

• Principal Investigator at OCWD

Wastewater surveillance (WS), when coupled with advanced molecular techniques, offers near real-time monitoring of community-wide transmission of SARS-CoV-2 and allows assessing and mitigating COVID-19 outbreaks, by evaluating the total microbial assemblage in a community. Composite wastewater samples (24 h) were collected weekly from a manhole bet...

Microbial contamination of recreation waters is a major concern globally, with pollutants originating from many sources, including human and other animal wastes often introduced during storm events. Fecal contamination is traditionally monitored by employing culture methods targeting fecal indicator bacteria (FIB), namely E. coli and enterococci, w...

Regulated public drinking and bottled waters are microbially safe for public consumption, but they aren't intended to be completely free of microorganisms. In a recent study (https://bit.ly/326y5oa) at the Maryland Pathogen Research Institute, University of Maryland, we analyzed tap, drinking fountain, and bottled water using DNA sequencing technol...

The microbiological content of drinking water traditionally is determined by employing culture-dependent methods that are unable to detect all microorganisms, especially those that are not culturable. High-throughput sequencing now makes it possible to determine the microbiome of drinking water. Thus, the natural microbiota of water and water distr...

Microorganisms are ubiquitous in the biosphere, playing a crucial role in both biogeochemistry of the planet and human health. However, identifying these microorganisms and defining their function are challenging. Widely used approaches in comparative metagenomics, 16S amplicon sequencing and whole genome shotgun sequencing (WGS), have provided acc...

Microbiological risks associated with drinking water can be minimized by providing enhanced integrity monitoring of bacterial removal by water treatment processes. This study aimed to evaluate the efficacy of real-time bacteriological counters for continuously assessing the performance of a full-scale sand filter to remove bacteria. Over the course...

Safety of potable reuse can be enhanced by improved water quality monitoring techniques for assessing water treatment processes. This study evaluated the efficacy of online bacterial counting for continuous monitoring of reverse osmosis (RO) membranes to remove bacteria using real-time bacteriological commercial counters and an on-site pilot-scale...

Conventional water resources are not sufficient in many regions to meet the needs of growing populations. Due to cyclical weather cycles, drought, and climate change, water stress has increased worldwide including in Southern California, which serves as a model for regions that integrate reuse of wastewater for both potable and non-potable use. The...

Rigorous monitoring of microbial water quality is essential to ensure the safety of recycled water after advanced treatment for indirect and direct potable reuse. This study evaluated real-time bacterial monitoring for assessing reverse osmosis (RO) treatment for removal of bacteria. A strategy was employed to monitor bacterial counts on-line and i...

Research scientists are making strides to advance the safety and application of potable water reuse through the use of metagenomics for water quality analysis

Next-generation sequencing (NGS) and metagenomics were used to identify microbial communities in biofilms of microfiltration (MF) and reverse osmosis (RO) membranes in an advanced water purification facility (AWPF) that treats municipal wastewater to produce potable quality water. Secondary treated wastewater effluent is the source of influent to t...

Current microbial source tracking (MST) methods for water depend on testing for fecal indicator bacterial counts or specific marker gene sequences to identify fecal contamination where potential human pathogenic bacteria could be present. In this study, we applied 454 high-throughput pyrosequencing to identify bacterial pathogen DNA sequences, incl...

Assimilable organic carbon (AOC) is commonly used to measure the growth potential of microorganisms in water, but has not yet been investigated for measuring microbial growth potential in soils. In this study, a simple, rapid, and non-growth based assay to determine AOC in soil was developed using a naturally occurring luminous strain Vibrio harvey...

The contamination of water resources by nonpoint-source fecal pollution is a major concern to human health and water quality throughout the world. The Santa Ana River (SAR) in southern California is an impaired stream with historically high fecal coliform counts. This study evaluated the presence of indicator bacteria at 13 sites in the middle Sant...

Pollution of water resources is a major risk to human health and water quality throughout the world. The purpose of this study was to determine the influence of pollutant sources from agricultural activities, urban runoffs, and runoffs from wastewater treatment plants (WWTPs) on bacterial communities in a low-flowing river. Bacterial community stru...

Microbial growth can be a significant issue for reverse osmosis (RO) and microfiltration (MF) processes in the water industry. Microbial growth or regrowth can affect plant performance and increases plant operation costs. Assimilable Organic Carbon (AOC) is the fraction of the total organic carbon (TOC) that bacteria can use for growth and other me...

The Santa Ana River (SAR) in southern California, USA is an impaired stream with historically high fecal coliform counts. This study evaluated the presence of indicator bacteria in 13 sites in the middle Santa Ana River watershed (MSAR). The objectives of this study were to: (i) examine spatial and temporal characteristics of fecal bacteria loading...

The prevalence of Escherichia coli O157 associated with different sources of fecal pollution was determined in a 12-month study in the middle Santa Ana River Watershed of southern California. Water and sediment samples were collected from 17 locations throughout the watershed for the isolation of E. coli O157. A total of 153 presumptive E. coli O15...

To correlate microbial community composition and water quality changes within wetland cells containing varying plant densities and composition in a free water surface (FWS) constructed wetland. Water chemistry was monitored weekly for nitrate, orthophosphate, and suspended solids, at various sites throughout the wetland for 6 months. Treatment pond...

The Santa Ana River in Southern California is the primary water supply for about 2 m people. The river originates in the San Gabriel and San Bernardino Mountains at elevations of more than 10,000 feet and flows southwesterly for more than 100 miles before discharging into the Pacific Ocean at Huntington Beach. The watershed is home to more than 4 m...

Santa Ana River in Southern California and its tributaries drain the largest volume of water among all rivers in Southern California. Most of the surface flow from the river is diverted to aquifers that supply water to approximately 2 million people. Chino Creek, a tributary of Santa Ana River (SAR), is an impaired water body due to pathogens and n...

Parallel experiments using a blend of surface waters were conducted to evaluate differential fouling rates among reverse osmosis (RO) membranes when operated under pilot- vs. full-scale conditions. Testing was conducted using a 230 L/min conventional (rapid mix/flocculation/sedimentation/filtration) package plant (CPP) and a 2,000 ML/d fullscale tr...

Pseudomonas putida 54g grew on mineral salts with toluene and exhibited catechol-2,3-dioxygenase (C23O) activity, indicating a meta pathway. After 10 to 15 days on toluene, nondegrading (Tol-) variants approached nearly 10% of total CFU. Auxotrophs were not detected among variants, suggesting selective loss of catabolic function(s). Variant formati...