Orange County Water District Research Articles

X-ray Absorption Spectroscopy Reveals Mechanisms of Calcium and Silicon Fouling on Reverse Osmosis Membranes Used in Wastewater Reclamation

Reverse osmosis (RO) is widely employed to provide clean water from nontraditional sources (e.g., seawater or municipal wastewater). One of its key challenges is membrane fouling, which leads to reduced flux and increased operational costs. Despite its practical relevance, fundamental understanding of membrane fouling is limited. Toward this end, we investigated calcium (Ca) and silicon (Si) fouling under real RO feed conditions using μ-X-ray fluorescence (μ-XRF) mapping and μ-X-ray absorption near-edge fine structure (μ-XANES) spectroscopy. These techniques are distinctly suited to identify the spatial distribution and (local) chemical speciation of foulants, thereby providing unique insight into the mechanisms of fouling under realistic conditions. Specifically, we investigated RO membranes harvested from a pilot-scale RO system operated at the Orange County Water District (OCWD) Groundwater Replenishment System (GWRS) Advanced Water Purification (AWP) Facility, which received the same feed water as the full-scale plant. Both Ca and Si were found to be abundant in the fouling layer. Despite the use of a commercial antiscalant to inhibit mineral formation, several Ca minerals were present in the fouling layer as minority species, including sulfates, phosphates, and carbonates; most of these minerals were found in particles that were aligned with the feed spacer used to separate the membranes. In contrast, organic-bound Ca and silica occurred across the entire membrane. Our work provides novel insight into the synergistic mechanism of RO fouling by Ca, Si, and organics on RO membranes.

Membrane aging effects on water recovery during full-scale potable reuse: Mathematical optimization of backwashing frequency for constant-flux microfiltration

One tool in efforts to tackle the ever growing problem of water scarcity is municipal wastewater reclamation to produce drinking water. Microfiltration (MF) is a central technology for potable reuse because it is highly effective in removing pathogenic protozoa, bacteria, and other colloids and for reverse osmosis pretreatment. However, as microfiltered materials accumulate at the membrane surface, its productivity is reduced requiring periodic removal of foulants. A mathematical model of MF is described in the context of hollow fiber filtration that focused on optimizing constant flux operation with backwashing. Design curves were also proposed for determining backwash timing. The model analysis is evaluated against real-world MF fouling for membranes that range in age from a few weeks to three years, observed at the world’s largest water reuse facility operated by the Orange County Water District. The presented model compares well with the full-scale operational data, and model parameters accurately capture variations in fouling kinetics with membrane age, providing clues to changes in optimal regeneration timing and frequency as membrane performance declines over long time scales.

Groundwater Recharge to Address Seawater Intrusion and Supply in an Urban Coastal Aquifer

The Orange County Water District (OCWD) was created in 1933 by the California Legislature and tasked with managing water resources in Orange County. As a part of its strategy to fight seawater intrusion and guarantee a reliable groundwater supply in the basin, OCWD built a recycled wastewater facility that treats wastewater received from the Orange County Sanitation District and recharges the water into the basin through injection wells and infiltration ponds. OCWD’s first recycled wastewater facility, Water Factory 21, began operating in 1975 and was replaced in 2008 by the Groundwater Replenishment System (GWRS). Recharged water not serving as a barrier for seawater instruction is pumped by local water districts and municipalities (referred to as “producers”), who pay a pumping fee to OCWD. Water provided by GWRS is both more reliable and less expensive for the producers than water acquired from other sources, including imported surface water. In responding to the recognized threat of seawater intrusion, OCWD owes its success to creatively enabling recharge through the development of novel source water. OCWD’s broad purview and authority to manage groundwater, combined with its effective implementation and long-term stewardship of the recharge program as it has evolved over many years, have enabled innovation in MAR using treated wastewater.

AWWA Water Science Author Spotlight

Having recently published an article in AWWA Water Science, Megan Plumlee answered questions from the publication's editor-in-chief, Kenneth L. Mercer, about the research. Real-Time Reverse Osmosis Monitoring for Antiscalant Dose Selection in Advanced Treatment of Wastewater Anditya Rahardianto, Han Gu, Bilal M. Khan, and Megan H. Plumlee Megan Plumlee visits Huntington State Beach in Southern California. Right now our team at the Orange County Water District (OCWD) is especially focused on per- and polyfluoroalkyl substances (PFAS), such as exploring novel treatment methods for removing PFAS from drinking water. We're also studying ways to demonstrate, and therefore get appropriate credit for, enteric virus removal during advanced water purification as part of potable reuse of (waste)water. Broadly speaking, we research topics relevant to our organization. OCWD (Fountain Valley, Calif.) manages a groundwater aquifer and employs potable reuse. Megan (front row, at left) is a member of the Research and Development Department at Orange County Water District in Fountain Valley, Calif. Department staff gather at a holiday luncheon in 2019. I remember fondly my undergraduate chemistry professor and advisor, who passed away recently, Jim Currie of Pacific University. He was humble and kind. He pushed me to apply to a lot of really noteworthy and famous universities to pursue my PhD; I don't think I would have reached so high or been so confident on my own. I ended up at Stanford for my master's and PhD degrees. I thank you—and miss you—Professor Currie. Our best work is through collaborations since people always do better in a team with diverse inputs and different drivers. For this project, we wanted to collaborate with the developer (Noria Water Technologies out of University of California, Los Angeles) on their new and improved technology (RO-SpotlightTM) to explore practical applications of a novel sensor in our treatment plant. The overarching goal is to be able to better manage and address the inevitable fouling and scaling of reverse osmosis membranes through better, real-time data. Because people are only human and don't have computer brains (yet), I think our biggest challenge across all of science and engineering is how to better solve problems via systems-level thinking. Since we aren't connected with a hive mind, I suspect that people are inefficiently working on the “same” problems over and over again in different fields or even the same field. What solutions can we environmental engineers or chemists adopt from, say, medicine or materials science or food science? As we strive to make recycling water for potable use more efficient and therefore less expensive, I hope it will open up the feasibility of this water supply for other communities. Especially now with telecommuting every day and having gotten awfully comfortable with it in my armchair, I am trying to avoid being too sedentary. I walk my dogs every day, prepare nearly all my food from scratch (including bread and oat milk), and I literally run up and down the stairs as much as possible as a sorry form of exercise. To learn more about Megan's research, visit the article online at https://doi.org/10.1002/aws2.1196. This article is part of the Topical Collection on Potable Reuse. Visit https://news.awwa.org/reuse-collection to learn more about this collection.

Degradation of contaminants of emerging concern by UV/H2O2 for water reuse: Kinetics, mechanisms, and cytotoxicity analysis

Advanced oxidation using UV and hydrogen peroxide (UV/H2O2) has been widely applied to degrade contaminants of emerging concern (CECs) in wastewater for water reuse. This study investigated the degradation kinetics of mixed CECs by UV/H2O2 under variable H2O2 doses, including bisphenol A, estrone, diclofenac, ibuprofen, and triclosan. Reverse osmosis (RO) treated water samples from Orange County Water District’s Groundwater Replenishment System (GWRS) potable reuse project were collected on different dates and utilized as reaction matrices with spiked additions of chemicals (CECs and H2O2) to assess the application of UV/H2O2. Possible degradation pathways of selected CECs were proposed based on high resolution mass spectrometry identification of transformation products (TPs). Toxicity assessments included cytotoxicity, aryl hydrocarbon receptor-binding activity, and estrogen receptor-binding activity, in order to evaluate potential environmental impacts resulting from CEC degradation by UV/H2O2. Cytotoxicity and estrogenic activity were significantly reduced during the degradation of mixed CECs in Milli-Q water by UV/H2O2 with high UV fluence (3200 mJ cm−2). However, in GWRS RO-treated water samples collected in April 2017, the cytotoxicity and estrogen activity of spiked CEC-mixture after UV/H2O2 treatment were not significantly eliminated; this might be due to the high concentration of target CEC and their TPs, which was possibly affected by the varied quality of the secondary treatment influent at this facility such as sewer-shed and wastewater discharges. This study aimed to provide insight on the impacts of post-UV/H2O2 CECs and TPs on human and ecological health at cellular level.

UV/chlorine vs. UV/H2O2 for water reuse at Orange County Water District, CA: a pilot study

On-site demonstration tests evaluated 1,4-dioxane removal in reverse osmosis permeate (RO permeate) at the Orange County Water District (OCWD) Advanced Water Purification Facility (AWPF).

Groundwater in California: From Juridical and Biopolitical Governmentality to a Political Physics of Vital Processes

This article analyzes the emergence of a political rationality of groundwater in contemporary California. It contrasts a new government of nature that we call a ‘political physics of vital processes’, operative in the case of the Orange County Water District, with juridical and biopolitical rationalities of groundwater governance. To do so, we propose a genealogical account grounded in a reading of a key concept in Aristotle’s first book of Politics. The case is analyzed along the axes of subjectivity, space, and temporality, opening to a novel way of conceptualizing the relation between power and nature.

Characterization of the Microbiome at the World’s Largest Potable Water Reuse Facility

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 Orange County Water District (OCWD) Advanced Water Purification Facility (AWPF) is a highly engineered system designed to treat and produce up to 100 million gallons per day (MGD) of purified water from a municipal wastewater source for potable reuse. Routine facility microbial water quality analysis is limited to standard indicators at this and similar facilities. Given recent advances in high throughput DNA sequencing techniques, complete microbial profiling of communities in water samples is now possible. By using 16S/18S rRNA gene sequencing, metagenomic and metatranscriptomic sequencing coupled to a highly accurate identification method along with 16S rRNA gene qPCR, we describe a detailed view of the total microbial community throughout the facility. The total bacterial load of the water at stages of the treatment train ranged from 3.02 × 106 copies in source, unchlorinated wastewater feed to 5.49 × 101 copies of 16S rRNA gene/mL after treatment (consisting of microfiltration, reverse osmosis, and ultraviolet/advanced oxidation). Microbial diversity and load decreased by several orders of magnitude after microfiltration and reverse osmosis treatment, falling to almost non-detectable levels that more closely resembled controls of molecular grade laboratory water than the biomass detected in the source water. The presence of antibiotic resistance genes and viruses was also greatly reduced. Overall, system design performance was achieved, and comprehensive microbial community analysis was found to enable a more complete characterization of the water/wastewater microbial signature.

Newspaper Coverage of Potable Water Recycling at Orange County Water District’s Groundwater Replenishment System, 2000–2016

Water planners in water-strapped communities in the western United States and beyond increasingly consider potable water recycling an important water management strategy. Although potable water recycling can increase an otherwise limited urban water supply, the threat of public or political opposition often looms large. This paper examines newspaper coverage of the most widely celebrated potable water reuse project in the world—the Groundwater Replenishment System (GWRS) in Orange County, California, USA. The case study examines the coverage of GWRS contained in local, national, and international newspapers during an era of significant investment and repeated expansion. Despite the potential controversy associated with drinking recycled wastewater, there was no negative newspaper coverage of GWRS from 2000–2016. Much of the coverage was mundane, however several articles embraced infrastructure and technology as key to developing new water resources while protecting public and environmental health. Although potable water recycling is presented as an innovative solution capable of solving several problems at once, a close analysis reveals that recycled water may not fulfill the promise of an uninterruptible urban water supply.

Maximizing Infiltration Rates by Removing Suspended Solids: Results of Demonstration Testing of Riverbed Filtration in Orange County, California †

Clogging due to the accumulation of suspended solids is a major constraint that limits the capacity of Orange County Water District’s (OCWD) surface water recharge system. In order to decrease clogging and increase system capacity, OCWD is testing the ability of riverbed filtration to reduce suspended solids concentrations and improve recharge rates. Riverbed filtration is achieved through a shallow subsurface collector system placed approximately one meter below the surface. Filtered water from the collector system is conveyed by gravity to the receiving recharge basin. Initial results show that riverbed filtration is highly effective in removing suspended solids in the recharge water, which in turn also greatly increases the recharge capacity of the receiving basin. Some other water quality benefits are also achieved. Data collected thus far indicate that it will be cost-effective to use this approach at a larger scale to capture and recharge increased quantities of storm flow obtained from the Santa Ana River.

Innovative Approaches to Collaborative Groundwater Governance in the United States: Case Studies from Three High-Growth Regions in the Sun Belt.

Groundwater is an increasingly important source of freshwater, especially where surface water resources are fully or over-allocated or becoming less reliable due to climate change. Groundwater reliance has created new challenges for sustainable management. This article examines how regional groundwater users coordinate and collaborate to manage shared groundwater resources, including attention to what drives collaboration. To identify and illustrate these facets, this article examines three geographically diverse cases of groundwater governance and management from the United States Sun Belt: Orange County Water District in southern California; Prescott Active Management Area in north-central Arizona; and the Central Florida Water Initiative in central Florida. These regions have different surface water laws, groundwater allocation and management laws and regulations, demographics, economics, topographies, and climate. These cases were selected because the Sun Belt faces similar pressures on groundwater due tohistorical and projected population growth and limited availability of usable surface water supplies. Collectively, they demonstrate groundwater governance trends in the United States, and illustrate distinctive features of regional groundwater management strategies. Our research shows how geophysical realities and state-level legislation have enabled and/or stimulated regions to develop groundwater management plans and strategies to address the specific issues associated with their groundwater resources. We find that litigation involvement and avoidance, along with the need to finance projects, are additional drivers of regional collaboration to manage groundwater. This case study underscores the importance of regionally coordinated and sustained efforts to address serious groundwater utilization challenges faced by the regions studied and around the world.

Quantifying Apparent Groundwater Ages near Managed Aquifer Recharge Operations Using Radio-Sulfur (35S) as an Intrinsic Tracer

The application of the cosmogenic radioisotope sulfur-35 (35S) as a chronometer near spreading basins is evaluated at two well-established Managed Aquifer Recharge (MAR) sites: the Atlantis facility (South Africa) and Orange County Water District’s (OCWD’s) Kraemer Basin (Northern Orange County, CA, USA). Source water for both of these sites includes recycled wastewater. Despite lying nearer to the outlet end of their respective watersheds than to the headwaters, 35S was detected in most of the water sampled, including from wells found close to the spreading ponds and in the source water. Dilution with 35S-dead continental SO4 was minimal, a surprising finding given its short ~3 month half-life. The initial work at the Atlantis MAR site demonstrated that remote laboratories could be set up and that small volume samples—saline solutions collected after the resin elution step from the recently developed batch method described below—can be stored and transported to the counting laboratory. This study also showed that the batch method needed to be altered to remove unknown compounds eluted from the resin along with SO4. Using the improved batch method, times series measurements of both source and well water from OCWD’s MAR site showed significant temporal variations. This result indicates that during future studies, monthly to semi-monthly sampling should be conducted. Nevertheless, both of these initial studies suggest the 35S chronometer may become a valuable tool for managing MAR sites where regulations require minimum retention times.

Post‐treatment Optimization to Enhance Groundwater Recharge Operations

A recent expansion of Orange County (Calif.) Water District's advanced water purification facility allowed the enhancement of energy‐recovery devices on new reverse osmosis units, secondary effluent flow equalization, and alternative treated water quality targets.

Groundwater management: a search for better policy combinations

Excessive groundwater pumping is now a global concern. There is no panacea for this problem, which needs to be addressed through continual policy improvements based on case studies. Good examples of the diversity of groundwater management are demonstrated by the Tokyo (Japan) and Orange County Water District (OCWD, California, USA) experiences. In Tokyo, excessive groundwater pumping was addressed through technological restrictions, including restrictions on the diameter and depth of wells, and construction of industrial waterworks. On the other hand, in Orange County, OCWD introduced a pump tax to purchase external water for artificial groundwater recharge. These two strategies are in striking contrast, from two perspectives. First, while OCWD's main policy tools were tax and artificial recharge, Tokyo depended on technological restrictions and construction of waterworks. Second, OCWD uses a combination of surface water and groundwater, but water supply in Tokyo has shifted almost completely from groundwater to surface water. What are the strong and weak points of each strategy? What causes such diversity? In this paper, a comparative case study was conducted to clarify (1) the institutional contexts causing the diversity of groundwater management and (2) the advantages and disadvantages of each policy combination.

Identifying, Evaluating, and Implementing Antiscalants in RO Reuse Applications

AbstractThe Orange County Water District (OCWD) operates a 70-mgd RO system as part of the Groundwater Replenishment System (GWRS), an advanced wastewater purification facility. Each of 15 5-mgd RO units consists of a three-stage array, operating at 85 percent recovery. As part of the operating strategy, antiscalant and pH suppression are used to limit third-stage precipitation of sparingly soluble mineral salts. Identifying successful antiscalants is extremely challenging. A variety of antiscalants with varying chemistries and capabilities present opportunities for optimizing RO processes, pricing, dosage, and pH adjustment. Recognizing the potential savings in RO pretreatment chemical cost, OCWD began antiscalant pilot-scale trials in 2009. However, failure to identify an effective product led to the trial's cancellation. Concurrently, the GWRS RO facility began experiencing third-stage permeability loss in all 15 RO units because the antiscalant was ineffective. This article discusses fast-track testin...

Improving Performance and Reducing Costs in Reclaiming Secondary Municipal Waste

AbstractThe Orange County Water District of Southern California conducted side-by-side testing of the latest reverse osmosis (RO) membrane technology and membranes currently operating in the district's Groundwater Replenishment System. The new RO elements were installed in a satellite vessel attached to the first stage of an existing three-stage train. New membrane performance was monitored for seven months and compared with the performance of the existing membranes, which had been operating for two years. Construction of the new elements included a thicker (34-mil) spacer, leading to less differential pressure loss and less fouling potential. The new elements had the same membrane area as the existing elements and, therefore, could be operated at the same flux and flow. This article compares operating data to demonstrate the new membrane's improved performance, RO membrane chemistry, and element design. The data demonstrate the new membrane's potential for reducing operating costs in a full-scale system.

Molecular characterization of effluent organic matter identified by ultrahigh resolution mass spectrometry

Effluent dissolved organic matter (EfOM) collected from the secondary-treated wastewater of the Orange County Sanitation District (OCSD) located in Fountain Valley, California, USA was compared to natural organic matter collected from the Suwannee River (SRNOM), Florida using ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Furthermore, the two different treatment processes at OCSD, activated sludge and trickling filter, were separately investigated. The blend of these two effluents was further evaluated after it had passed through the microfiltration process of the Advanced Water Purification Facility (AWPF) at Orange County Water District (OCWD). EfOM contained 872 different m/ z peaks that were unambiguously assigned to exact molecular formulae containing a single sulfur atom and carbon, hydrogen and oxygen atoms (CHOS formulae). In contrast, the SRNOM sample only contained 152 CHOS formulae. The trend in CHO molecular compositions was opposite with 2500 CHO formulae assigned for SRNOM but only about 1000 for EfOM. The CHOS-derived mass peaks with highest abundances in EfOM could be attributed to surfactants such as linear alkyl benzene sulfonates (LAS), their co-products dialkyl tetralin sulfonates (DATS) and their biodegraded metabolites such as sulfophenyl carboxylic acids (SPC). The differences between the treatments were found minor with greater differences between sampling dates than treatment methods used.

Converting BOD to Nitrification/Denitrification in Same Reactor While Maintaining Capacity

Converting BOD to Nitrification/Denitrification in Same Reactor While Maintaining CapacityThe Orange County Sanitation District (OCSD) modified their activated sludge operation from biochemical oxygen demand (BOD) to nitrification-denitrification (NDN) mode to reduce ammonia discharged and sent to the Groundwater Replenishment System (GWRS) operated by Orange County Water District. Full scale verification tests were conducted following conversion to NDN. The conversion to NDN was...Author(s)J.B. NeethlingBruce WilleyAdam NicholsMichelle HetheringtonDave HeinzRon WadeWendy SevenandtSourceProceedings of the Water Environment FederationSubjectSession 103: Developments in Nitrogen RemovalDocument typeConference PaperPublisherWater Environment FederationPrint publication date Jan, 2011ISSN1938-6478SICI1938-6478(20110101)2011:8L.6627;1-DOI10.2175/193864711802793317Volume / Issue2011 / 8Content sourceWEFTECFirst / last page(s)6627 - 6637Copyright2011Word count130Subject keywordsNitrification-DenitrificationSecondary TreatmentConvert BOD to NDN

Comparing Membrane Operations at Three of the World's Largest Advanced Water Treatment Plants

Within the last decade, wastewater reclamation using membrane technologies has become a realistic possibility for many municipalities and a necessity for those located in dry, arid regions. The combination of membrane filtration, reverse osmosis (RO), and advanced oxidation to treat municipal effluents beyond drinking water qualities has been demonstrated as the process of choice for municipalities trying to reduce dependence on potable water for industrial or agricultural uses, implement indirect potable reuse applications, or create direct potable reuse supplies. Three such municipalities—West Basin Municipal Water District, Carson, Calif.; Orange County Water District, Fountain Valley, Calif; and the Western Corridor Recycled Water Project, Brisbane, Queensland, Australia—have employed this advanced treatment process on their local wastewater effluents for a variety of uses, but their common goal is to sustain local potable water supplies. This article compares operational data and performance for each of these large-scale water recycling facilities. Particular attention is paid to the microfiltration and RO systems, startup, and ongoing issues experienced at each location.

The Groundwater Replenishment System

This article provides an overview of the Groundwater Replenishment (GWR) System, operated by the Orange County Water District in southern California. It is the world's largest water purification and reuse project of its kind. The GWR system benefits are presented, along with its various components, the use of grant money to reduce the total project cost, specific quality requirements of the project, brief summary of operational experiences, and the visionary partnership resulted in advancing water reuse.