Fevig, Stephanie

Stephanie is a Research Program Manager at the Water Research Foundation in Denver. She has been with WRF since February 2018 and she currently manages a variety of projects focused on nutrients treatment, co-digestion, biosolids, and water reuse. She has experience in wastewater process modeling and design, process mechanical design, facility planning, asset management, and project management. She has a Masters degree in Environmental Engineering from Colorado School of Mines and a Bachelors degree in Chemical Engineering from New Mexico State University.

Titles from this speaker

Advancing Low-Energy Biological Nutrient Removal through Low Dissolved Oxygen Operation: Is Biological Selection the Key?

Abstract

Introduction In the activated sludge process (ASP), dissolved oxygen (DO) is an important factor for aeration cost, nitrification efficiency, nutrient removal, and N2O emission. Even though, the term 'low DO' has been used in a somewhat subjective manner and can vary depending on the context and specific requirements, the overall objective of this study is to pave the way for full-scale implementation of low DO BNR through scientific investigation to systematically answer questions on the impact of DO concentrations on nitrification, denitrification, BPR, microbial ecology, and greenhouse gas emissions. This abstract presents results developed as part of the WRF No. 5083 titled 'Advancing Low-Energy Biological Nitrogen and Phosphorus Removal.' Methodology To quantify the impact and benefits of low DO operation in the capacity and performance of existing ASP, several participating facilities that were operating at low DO and high DO conditions were studied as part of this project. Long-term operational data from the facilities was assessed and compared with the baseline information collected during the literature review. Mixed liquor samples from the participating utilities were collected and assessed through lab-scale studies. Low dissolved oxygen control and batch test procedures were developed as part of the project and used to investigate the impact of low DO on biokinetic rates. This information provided a unique comparison and tabulation of important biokinetic parameters to better understand the implications of low DO BNR on plant capacity and performance. In addition, this provides guidelines for the selection of proper important biokinetic coefficients for process modeling. Results and Discussion Bench-scale, and full-scale experiments were conducted to investigate the impact of DO concentrations on nitrification, denitrification, BPR, microbial ecology, and N2O emissions with the goal to advance low DO BNR. The following biokinetic insights were collected as part of this study. Nitrification: Specific nitrification rates for ASP operating with long-term exposure to low DO conditions were approximately 60-80% of the nitrification rates at high DO as presented in Figure 1. This study concluded that long-term low DO operation results in a shift in the nitrifier community structure, with comammox, and in some case ammonia oxidizing archaea, being selected over ammonia oxidizing bacteria. Experimental results confirm that these communities selected under stable low DO operation have a higher oxygen affinity than AOB and Nitrobacter-related NOB. TIN Removal: The maximum TIN removal rates were found at DO concentrations ranging from 0.2 to 0.5 mg/L. At this DO range, the nitrification rate equals the denitrification rate, which would therefore lead to complete SND in non-carbon limiting conditions as depicted in Figure 2. At DO concentrations of less than 0.2 mg/L, the TINRR is inhibited by nitrification and at DO concentrations higher than 0.5 mg/L, TINRR is limited by denitrification. This observation may change from plant to plant since there are multiple parameters that could affect the results including floc size and porosity, mixing intensity, and microbial population. Biological Phosphorus Removal: Biological phosphorus removal is not impacted by low DO operation. Based on the experimental results from 12 full-scale plants, the low DO phosphorus uptake rates measured in this study were higher compared to the P uptake rates for high DO/ conventional systems. Phosphorus uptake rates slows down significantly when the DO is 0.1 mg/L suggesting that the KDO for PAO is lower around 0.1 mg/L. N2O Emissions: In this work, pilot and bench-scale testing demonstrated that long-term exposure of biomass to low DO does not result in an increase in total N2O emissions (Fig. 3a). Even though this study did not investigate the specific N2O production mechanisms and pathways associated with low DO BNR, the work suggests that the N2O emissions are lower than conventional high DO systems since the relative abundance of AOB and Nitrobacter-related NOB are relatively low (Fig. 3b) limiting the N2O produced via NH2OH oxidation pathway and nitrifier denitrification by AOB. In the low DO BNR systems, Nitrospira-related NOB and comammox were dominant nitrifiers suggesting they do not have the same reduction pathways of NO2 and NO to N2O and therefore produce less N2O comparable to AOB. Conclusion DO is an important parameter influencing aeration cost, nitrification efficiency, nitrogen and phosphorus removal efficiency, treatment plant capacity and N2O emission. As presented in this study, there are several WRRF that utilize low DO operation in the ASP achieving effluent water quality with respect to N and P and require less energy than conventional ASP. The DO setpoints in such plants vary depending on loading conditions, aeration controls, and operator's preferences. Therefore, selecting a single DO setpoint to represent low DO BNR is difficult. Based on the experimental results obtained during this study, low DO can be defined as the bulk liquid DO concentration or range in the aerobic zones where simultaneous N and P removal reactions occur, often ranging from 0.2 mg/L to 0.5 mg/L. Results from this study demonstrate that long-term exposure to biomass at these DO concentrations allow for biological selection of microorganisms with very high oxygen affinities.

In the ASP, DO is an important factor for cost, nitrification efficiency, and N2O emission. The objective of this study was to investigate the impact of DO concentrations on nitrification, denitrification, BPR, microbial ecology, and N2O emissions. Based on the experimental, low DO can be defined as the DO concentration or range in the aerobic zones where SND reactions occur, often ranging from 0.2 to 0.5 mg/L allowing for biological selection of microorganisms with very high oxygen affinities.

SpeakerJimenez, Jose

Presentation time

13:40:00

13:50:00

Session time

13:30:00

15:00:00

SessionMicrobial Ecology Selection Under Low DO Concentration

Session number409

Session locationRoom 253

TopicAdvanced Level, Energy Production, Conservation, and Management, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Jimenez, Jose, Miller, Mark, Bauhs, Kayla, Sturm, Belinda, Wittman, Megan, Dold, Peter, Fevig, Stephanie

Author(s)J.A. Jimenez1, M. Miller2, K. Bauhs3, B. Sturm4, M. Wittman4, P. Dold5, S.M. Fevig6

Author affiliation(s)1Brown and Caldwell, FL, 2Brown and Caldwell, NC, 3Brown and Caldwell, TN, 4University of Kansas, KS, 4, 5Envirosim Associates Ltd., ON, 6South Platte Renew, CO

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159576

Volume / Issue

Content sourceWEFTEC

Word count16

Description: WRF Research Highlights: New Discoveries and Tools to Support Your Co-Digestion...

WRF Research Highlights: New Discoveries and Tools to Support Your Co-Digestion Program

Abstract

Functioning at the nexus of the food, energy, and wastewater systems, co-digestion is one of the linchpin processes used to produce renewable energy from biogas and treat and transform food and municipal wastes into marketable products (WRF, 2019). Co-digestion with organic feedstocks can improve digester performance, increase methane production for energy generation, and decrease operating costs. US EPA has identified food waste as one of the least recovered materials in the municipal solid waste industry, making up 20% of national municipal solid waste. Because of this and other independent drivers, states such as California and Massachusetts have adopted initiatives to reduce the amount of organic waste accepted at municipal landfills. A shifting regulatory landscape is leading WRRFs to evaluate co-digestion with residential and commercial food waste from post-consumer sources. For over a decade and with over seventeen publications to date, The Water Research Foundation (WRF) has advanced the science and shared the knowledge through collaborations and funding co-digestion research covering US and international case studies, operational side-effects and other impacts, business case analyses, biogas production, and even co-digestion of manure. WRF is the leading research organization advancing the science of all water to meet the evolving needs of its subscribers and the water sector. WRF is a nonprofit, educational organization that funds, manages, and publishes research on the technology, operation, and management of drinking water, wastewater, reuse, and stormwater systems-all in pursuit of ensuring water quality and improving water services to the public. WRF serves approximately 1,200 subscribers, hosts an online research library of more than 2,300 projects, and manages an innovation platform with a database of more than 140 innovative technologies. In 2016, WRF began focusing research on source separated organic (SSO) feedstocks. Co-digestion with organic feedstocks can improve digester performance, increase methane production for energy generation, and decrease operating costs. SSO feedstock is defined as originating from commercial generators such as restaurants (excluding grease), commercial kitchens and cafeterias, grocery stores, and residential generators separated from other wastes at the source. The purpose of this research is to provide utilities and practitioners with tools to access and communicate the applicability, costs, contractual scenarios, and benefits associated with source separated organic pre-treatment for co-digestion and various source separated organic supply management strategies. This presentation will share highlights, along with guidance and tools, from past research and focus on three recently completed WRF projects touching on different but interconnected aspects and stages of co-digestion: pre-treatment, contamination and characterization testing, and biogas quality. A summary of each project and key findings are presented below. Project 5037 (PI: Mohammad Abu-Orf, Hazen and Sawyer): Evaluation of Existing Source Separated Organic (SSO) Feedstock Pre-Treatment and Management Practices. Existing research on source separated organic co-digestion focuses on anaerobic digestion operational strategies and processes. There is minimal information on feedstock pre-treatment, characterization and management of contaminants, overall pre-treatment implementation and monitoring, and assessment of pre-treatment impacts on anaerobic digestion performance. This project provides the industry with a technical foundation, associated guidance materials, and utilitarian tools to more comprehensively understand the various methods currently in use or potentially suitable for pre-treatment of source separated organics. Key Outcomes: An SSO pretreatment database was constructed in PowerBI including: -Literature surveys and case studies to summarize the implementation and effectiveness of numerous pretreatment technologies. -Factsheets to expand the accessibility of technology information. -Detailed case studies with anecdotal recommendations which were formulated into figures to guide SSO pretreatment selection. -Experience of currently operating SSO pretreatment facilities including successes and challenges. Project 4915 (PI: Tanja Rauch-Williams, Carollo Engineers): Characterization and Contamination Testing of Source Separated Organic Feedstocks and Slurries for Co-Digestion at Resource Recovery Facilities. A key challenge with SSO feedstock co-substrate is that its composition, quality, and characteristics differ between geographical locations and can change over time. This causes challenges and uncertainties for pre-treaters, substrate brokers, facilities accepting this material, operators, engineers, and regulators. This project addresses these challenges by establishing guidelines for characterizing SSO feedstocks; standardizing sampling protocols for rapid and comprehensive monitoring of feedstocks; and developing recommendations for minimum feedstock quality requirements. Key Outcomes: There are four separate documents/reports included in this project: 1) Characterization of Source Separated Food Waste for Co-digestion in Water Resource Recovery Facilities aka Literature Review. This document provides a summary of background information on pertinent regulations, policies, SSO feedstock sources, and typical SSO food waste quality characteristics reported in literature. 2) Analytical Method Guidance for the Characterization of Source Separated Food Waste for Co-digestion in Water Resource Recovery Facilities. This document provides operators with a summary of recommendations on the sampling, preservation, and analysis of these parameters in SSO food waste feedstock to help overcome common issues with this challenging waste stream. 3) Towards a Uniform Basis for Substrate Characterization and Modeling of Anaerobic Co-Digestion and Anaerobic High-Strength Waste Treatment Workshop Summary. This document provides co-digestion practitioners with a focused discussion on the current status, achievements, and remaining challenges of using process modeling to simulate and predict co-digestion of HSW in anaerobic digesters at WRRFs. 4) The Relevance of Food Waste Quality for Co-Digestion Facility Planning, Design, and Operation. This document provides practitioners with tools and guidance to assess the quality characteristics of different types of SSO feedstock and their impact on process performance, stability, regulatory compliance, and the quality of end products, including biosolids, biogas and air emissions, and final effluent. Project 4892 (PI: Ganesh Rajagopalan, Kennedy Jenks Consultants): Quality of Biogas Derived from Wastewater Solids and Co-Digested Organic Wastes: A Characterization Study. Co-digestion allows utilities to beneficially reuse organic matter and produce renewable energy. However, adding organic matter can result in unintended consequences to facility operation, such as digester foaming, sludge dewaterability, and odor. This project developed the scientific information needed to more accurately estimate emissions from anaerobic digesters that practice co-digestion, understand conditioning/pretreatment of raw biogas, and support the air quality permitting process for co-digestion. The research team created a predictive model to relate organic waste, including high-strength waste, and feed sludge characteristics to biogas quality. Key Findings: -Co-digestion of organic wastes with wastewater solids in anaerobic digesters in water resource recovery facilities (WRRFs) can enhance biogas yield (cu.ft./lb volatile solids reduced) as well as total biogas production. -Addition of organic wastes can alter biogas quality that may potentially impact regulatory compliance and/or treatment requirements. -Some organic wastes increased hydrogen sulfide levels in the biogas while others lowered the concentration. -Ammonia levels in biogas during co-digestion increased or decreased depending on the percent nitrogen content in the organic waste. -In general, several organic wastes appeared to increase the levels of volatile organic compounds (VOCs) in the biogas. In particular, the levels of acetone, butanone, ethanol, and butanol increased due to addition of the organic wastes tested in this study. -In most cases, addition of organic wastes appeared to lower the siloxane levels in the biogas.

This paper was presented at the WEF/IWA Residuals and Biosolids Conference, May 16-19, 2023.

SpeakerFevig, Stephanie

Presentation time

13:30:00

14:00:00

Session time

13:30:00

16:45:00

SessionSession 14: Co-Digestion

Session number14

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicResearch & Innovations