Steinle-Darling, Eva

Eva Steinle-Darling directs Carollos Water Reuse Technical Practice. She has a BSE in Chemical Engineering from Princeton University and an M.S. and Ph.D. in Environmental Engineering from Stanford University, where she studied the removal of PFAS using nanofiltration membranes. Her areas of technical expertise include membrane processes, advanced oxidation, filtration, disinfection, and other advanced treatment processes for microconstituent removal and management of microbial risks. She has supported regulatory guidance efforts for six US states, the National Water Research Institute, and the World Health Organization. As a member of the WateReuse Associations Regulatory and Policy Committee and a former Board Member, she is also leading education and advocacy efforts related to reuse across the U.S.

Titles from this speaker

Description: Demonstrating Real-Time Collection System Monitoring for Enhanced Source Control in...

Demonstrating Real-Time Collection System Monitoring for Enhanced Source Control in Potable Reuse

Abstract

WEFTEC, the largest water event of its kind in North America, offers water quality professionals the best in water quality education and training. With almost 200 technical sessions, workshops, mobile sessions, local facility tours and 1,000+ exhibitors, it is the premier water conference! The WEFTEC technical program is selected through a rigorous, peer-review process, ensuring that attendees experience the highest-quality education. WEFTEC speakers are experts and innovators, leading the way in water quality. The following paper was presented at WEFTEC 2020.

SpeakerSteinle-Darling, Eva

Presentation time

09:10:00

09:30:00

Session time

08:30:00

09:30:00

SessionReuse Water Quality: Control the Source

Session number533

TopicMicroconstituents, Water Reuse and Reclamation, Water Supply and Management

Author(s)

A. SalvesonP. CarloE. Steinle-DarlingE. Steinle-Darling

Author(s)A. Salveson1; P. Carlo1; E. Steinle-Darling2; E. Steinle-Darling2;

Author affiliation(s)Carollo Engineers, CA1; Carollo Engineers, TX2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157498

Volume / Issue

Content sourceWEFTEC

Word count13

Ion Exchange Potable Reuse: Organics and Salinity Removal Without RO

Abstract

An innovative treatment train, coined ion exchange-based advanced treatment (XBAT), was developed and validated for potable reuse. XBAT combines suspended ion exchange (SIX) and lime softening, which are integrated by regenerating the spent resin using bicarbonate. XBAT simultaneously removes TOC and salinity without the use of RO and the resulting concentrate disposal challenges. As such, XBAT provides the cost efficiency of non-RO based purification and the salt reduction of RO based purification. Salinity is the result of all dissolved anions and cations in water, which is often characterized by total dissolved solids (TDS). For potable reuse, salinity represents a specific challenge because wastewater effluents are typically more saline than the conventional surface water or groundwater that supplies a given community, and often exceeding drinking water standards. RO-based advanced treatment (RBAT) and carbon-based advanced treatment (CBAT) are the two prevailing advanced treatment approaches for potable reuse. Although RO rejects most dissolved salts, the resulting RO concentrate constitutes a large portion of total feed flow and creates a challenging residual disposal problem. CBAT integrates multiple treatment barriers for chemical and pathogenic contaminants, but none of the unit treatment processes removes measurable amounts of ionic salts. Therefore, there is a pressing need for an alternative treatment approach that overcomes the limitations of RBAT and CBAT by removing salinity without the residual challenge. To provide the efficiency of CBAT while providing the salt removal of RBAT, through years of research, our team developed an innovative treatment concept, namely ion eXchange-Based Advanced Treatment (XBAT), that simultaneously removes TOC and salinity without RO. XBAT consists of (1) suspended ion exchange (SIX) for the removal of negatively charged constituents (TOC, nitrate, sulfate, chloride, bromide, phosphate, etc.), (2) resin regeneration using bicarbonate, and (3) lime softening for cation (i.e., Ca, Mg) and excess bicarbonate removal (figure 1). SIX is a steady-state ion exchange process that keeps a strong base anion (SBA) resin fluidized in the reactor. A significant feature of SIX is its high resin regeneration frequency, which keeps the resin's ion exchange capacity only slightly utilized, thus allowing spent resin to be regenerated by a weaker and less concentrated regenerant (4% NaHCO3 in lieu of 10% NaCl). Bicarbonate regeneration adds alkalinity into SIX effluent, making the treated water more suitable for hardness removal and further TDS reduction through calcium carbonate precipitation. Figure 1 - Conceptual diagram of XBAT (IX with SBA resin and bicarbonate regeneration + lime softening) We have successfully demonstrated XBAT at the bench scale and evaluated its performance for TOC and salinity removal from secondary and tertiary wastewater effluents. Four resin types, two resin doses, three contact times, and their various combinations were tested over up to 50 resin exhaustion and regeneration cycles to assess long-term XBAT performance. Results indicated in figure 2 show an average TOC removal rate of 50% regardless of the effluent type and initial TOC concentrations. Average percent removal rates for sulfate, nitrate, bromide, and chloride were 99%, 90%, 94%, and 74%, respectively. Subsequent lime softening resulted in 92% calcium removal and 96% magnesium removal. Taken together, TDS decreased from an average of 680 mg/L down to 370 mg/L, achieving about 50% salinity reduction. This level of TDS removal would be sufficient to return effluent salinity levels to that of conventional drinking water sources, thus enabling the implementation of potable reuse without concerns about up-cycling conservative ions. A pilot study demonstrating XBAT has recently concluded (January 2024); results will be shared as part of this presentation. Figure 3 shows the XBAT pilot. Figure 2 Bench-scale results of bicarbonate-form IX performance on a tertiary effluent with four different resins Table 1 Bench-scale results of XBAT (SIX + softening) on tertiary effluent Figure 3 - XBAT Pilot - SIX (L) and Pellet Softener (R)

SpeakerPickett, Melanie

Presentation time

14:30:00

15:00:00

Session time

13:30:00

15:00:00

SessionEffective Strategies for Managing Organics in IPR/DPR Systems

Session number216

Session locationRoom 340

TopicIntermediate Level, Water Reuse and Reclamation

Author(s)

Pickett, Melanie, Yu, Rosa, Steinle-Darling, Eva, Hart, Vincent

Author(s)M. Pickett1, R. Yu2, E. Steinle-Darling3, V. Hart4

Author affiliation(s)1Carollo Engineers, Inc.2Carollo Engineers, Inc.3Carollo Engineers, Inc. 4Carollo Engineers, Inc.

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159674

Volume / Issue

Content sourceWEFTEC

Word count11

Putting DPR Rules Into Context: Regulatory Developments Across the United States

Abstract

The United States has a long history of successful water reclamation driven by a combination of effluent diversion and water supply scarcity. Both drivers have more recently resulted in a number of states working to develop regulations for direct potable reuse (DPR). Active regulatory processes include: (1) Texas, where DPR has been implemented in the absence of rules since 2013, and the 2021 state legislature passed a bill requiring its regulators to develop guidelines that will streamline DPR permitting; (2) California, which has just released its proposed DPR rules for public comment; (3) Florida, where the stakeholder-driven Potable Reuse Commission guidance is now helping shape a series of draft DPR regulations published by the FDEP, (4) Colorado, where state regulators are currently holding stakeholder workshops to help draft the language for future DPR rules, and (5) Arizona, where stakeholder-driven guidance and rulemaking recommendations were delivered to state regulators, who are now gearing up to draft regulations of their own. All of these efforts are also ongoing within the little-known context of DPR being allowed and regulated in two other US states: Ohio (since 2015) and North Carolina (since 2014).
Many stakeholders in these states and elsewhere will find themselves asking: What is the basis and rationale behind various parts of my state's approach to DPR? While the authors claim no prescience with regard to regulator intent in drafting their respective DPR rules, all regulatory progress is incremental and builds on prior work. Thus, the basis of much of the current draft rules can be found in various forms of prior guidance or regulations. This presentation will walk through guidance developed by Carollo and others through the progression of stakeholder processes in various US states that have gotten us to this point. We'll start with the 2015 National Water Research Foundation (NWRI) 'Framework for Direct Potable Reuse' and discuss how the major topics in that framework have evolved through various phases of regulatory development. Starting with the overarching public health and regulatory priorities that are consistent across all US-based guidance to-date, we'll define the key components of a sustainable DPR program, and how those have evolved since the 2015 NWRI Framework. We'll answer questions including: How do various jurisdictions define DPR? How have expectations changed around source control? Why are there different microbial log removal value (LRV) targets and what is their basis? What are the requirements around advanced treatment and how can we account for constituents of emerging concern (CECs)? How does monitoring differ in DPR compared to IPR and other reclaimed application? Attendees will leave the presentation understanding the background behind current regulatory trends for DPR and better prepared to discuss the merits of various regulatory approaches as DPR rules are finalized in various states.

Water supply scarcity and the desire to divert effluent have recently resulted in several states working to develop regulations for DPR. Many stakeholders find themselves asking: What is the basis and rationale behind various parts of my state's approach to DPR? This presentation will walk through the progression of stakeholder processes starting with the 2015 'Framework for Direct Potable Reuse' and discuss how major topics have evolved through various phases of regulatory development.

SpeakerSteinle-Darling, Eva

Presentation time

08:30:00

09:00:00

Session time

08:30:00

09:15:00

TopicIntermediate Level, Disinfection and Public Health, Facility Operations and Maintenance, Potable Reuse, Water Reuse and Reclamation

Author(s)

Steinle-Darling, Eva

Author(s)Eva Steinle-Darling1

Author affiliation(s)Carollo Engineers, Inc., TX1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158494

Volume / Issue

Content sourceWEFTEC

Word count12

Seven Habits of Highly Effective PFAS Source Trackers

Abstract

Abstract Summary

This presentation shares conclusions of Water Research Foundation's (WRF) Project #5082: Investigation of Alternative Management Strategies to Prevent PFAS from Entering Drinking Water Supplies and Wastewater. The study found it critical for utilities to characterize PFAS sources and minimize PFAS contamination of water resources, but they should be ready to address significant loads from domestic wastewater as well.

This presentation will include:
- A review of the importance of characterization of PFAS sources.
- A discussion of how implementing source control can reduce PFAS in a water resource recovery facility's (WRRF's) effluent and biosolids.

Introduction
Utilities are bracing for upcoming regulatory developments and exploring best approaches for monitoring, managing, and treating PFAS. Many technologies have been evaluated for PFAS removal, but effective treatment technologies are expensive. Thus, more research and policy emphasis are needed on preventing PFAS from entering water in the first place. WRF 5082 had the overall goal of developing actionable strategies for effective management of PFAS sources and providing guidance for utilities. In this presentation, the importance of characterization of PFAS sources will be reviewed, and a review will occur on how implementing source control can reduce PFAS in a WRRF's effluent and biosolids.

The goal of WRF 5082 was to develop actionable strategies for effective PFAS sources management for wastewater treatment and water reuse utilities. These strategies were developed by reviewing PFAS source databases, utility surveys of PFAS source control efforts, and conducting thorough PFAS mass balances in the sewersheds. The data and insights from these efforts then informed a guidebook for how utilities can track down and eliminate PFAS sources.

APPROACH AND RESULTS
The guidance developed through WRF 5082 outlines PFAS source control and mitigation in a seven-step process, as shown in Figure 1. These steps include developing a plan for identifying sources, identifying the sources and sampling, interpreting the results, and managing and mitigating sources of concern. The presentation will quickly review these steps and how utility surveys of monitoring, tracking, and mitigating PFAS provided practical information to industrial and municipal utilities for PFAS mitigation. The rest of the presentation will cover examples of how the steps can be utilized. It filled data gaps about the relative importance of different PFAS sources across wastewater, surface water, and groundwater through database analysis and detailed sampling campaigns.

The presentation will start with reviewing the impact of defacto reuse on PFAS concentrations entering wastewater facilities. Two PFAS source identification investigations will be reviewed — the Trinity River in Texas and Las Vegas (Nevada) Wash watersheds. The Las Vegas watershed investigation was a comprehensive mass balance, while the Trinity River investigation relied on the sweetener sucralose as a wastewater indicator. These studies looked at PFAS occurrence upstream and downstream of known wastewater treatment facilities, as shown in Figure 2. The studies identified that WRRF discharges comprised a majority of PFAS in local waterways, and that the artificial sweetener sucralose can be a cheap indicator of PFAS transport and occurrence since sucralose and PFAS are associated with anthropogenic activities.

The presentation will also discuss common sources of PFAS into collection systems and WRRFs. As part of WRF 5082, five wastewater collection systems across the country were sampled to investigate industrial and domestic/commercial PFAS sources, including firefighting and military areas, metal plating and finishing, textile manufacturing, landfill leachate, and airports. Figure 3 shows that, although the concentrations were high in PFAS from these sources, the mass loadings were less than half of what was supplied from domestic and commercial sources. This reiterates the need to understand the loading contribution of different PFAS sources.

The presentation will conclude with more recent data obtained from the Fifth Unregulated Contaminant Monitoring Rule (UCMR5) survey across the United States (US). Our most recent data analysis confirms that PFAS are widely detected in US surface waters, and that the main contributor is defacto reuse. However, the data also indicates that the frequency of PFOA and PFOS detection is decreasing, likely due to their ban in the early 2010s. Shorter chain PFAS are increasing as they are the replacements for PFOA and PFOS. This evolution in dominant PFAS will likely impact treatment strategies since shorter chains are more difficult to remove from wastewater.

Broader Impacts
This presentation is valuable to utilities, consultants, policy makers, and vendors as it reviews the systematic approach to identifying PFAS sources and approaching mitigation. Common industrial PFAS sources are reviewed, and the importance of quantifying industrial versus domestic/commercial sources will be discussed. In addition, current PFAS data from across the US is reviewed and put in context of how it might impact treatment strategies at wastewater facilities.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

14:30:00

14:45:00

Session time

13:30:00

15:00:00

SessionKnow What's Coming In: Source-Tracking of PFAS

Session locationMcCormick Place, Chicago, Illinois, USA

TopicContaminants of Emerging Concern & Trace Organics

Author(s)

Thompson, Kyle, Steinle-Darling, Eva, Young, Michelle

Author(s)K. Thompson1, E. Steinle-Darling1, M. Young1

Author affiliation(s)Carollo Engineers1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159929

Volume / Issue

Content sourceWEFTEC

Word count9

Description: What Happens in Texas Doesn't Stay in Texas: How a Small-Town Texas DPR Study...

What Happens in Texas Doesn't Stay in Texas: How a Small-Town Texas DPR Study Inspired an International Award-Winning Carbon-Based Direct Potable Reuse Demonstration (in Florida)

Abstract

The City of Dripping Springs is located in Hays County, Texas, twenty-five miles southwest of the State capital, Austin. The Austin metropolitan area is one of the fastest growing metropolitan areas in the nation (U.S. Census Bureau, 2014a). In addition, the U.S. Census Bureau ranked Hays County as the 14th fastest growing county in the U.S with a population increase of twelve percent between 2010 and 2013 (U.S. Census Bureau, 2014b). Like much of Texas over the past several years, the City has experienced drought conditions ranging from moderate to severe (U.S. National Drought Mitigation Center, 2015). Drought conditions, along with an increase in population, have led to strain on the City’s water supplies. Due to this confluence of factors, the City of Dripping Springs, Texas commissioned a feasibility study for direct potable reuse (DPR) in 2014, which was completed in 2015.

This paper discusses the genesis a first-of-its-kind proposal to produce purified drinking water from treated effluent using a process train that comprises ozone (O3), biologically active carbon (BAC), ultrafiltration (UF), granular activated carbon (GAC), and high-dose UV disinfection prior to chlorination, storage and distribution. This carbon-based advanced treatment (CBAT) approach was first established in a feasibility study in Texas, followed by implementation in a permanent 20 gpm demonstration facility in Florida. Intensive monitoring and sampling proved the ability to produce drinking water with this approach that meets all regulatory standards and an equivalent water quality to reverse-osmosis based treatment (RBAT).

SpeakerSteinle-Darling, Eva

Presentation time

13:52:00

14:07:00

Session time

13:30:00

15:00:00

SessionImplementation of Potable Reuse

Session number110

TopicDisinfection and Public Health, Policy and Regulation, Sustainability and Climate Change, Water Reuse and Reclamation, Water Supply and Management

Author(s)

Eva Steinle-Darling