Pifer, Leah

Leah Pifer is a process engineer with Black Veatch. Leah focuses primarily on wastewater treatment and nutrient removal upgrade design, but has also...

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About Pifer, Leah

Leah Pifer is a process engineer with Black Veatch. Leah focuses primarily on wastewater treatment and nutrient removal upgrade design, but has also engaged in many applied research projects within Black Veatchs innovation platform. Since she graduated with her masters in Environmental Engineering from the University of Michigan, her research focus has been on sustainability within wastewater treatment design with experience also in holistic life cycle analysis.

Pifer, Leah

Titles from this speaker

Modelling of Primary Sludge and RAS Fermentation for Carbon Management Optimization at WRRFs

Abstract

Introduction Conventional wastewater treatment plants are transitioning to integrated resource recovery and upcycling, which requires effective management of biodegradable organic carbon. This involves developing approaches to carbon diversion, such as anaerobic digestion of primary sludge and waste activated sludge for energy and fertilizer (Gavala et al 2003). Alongside the push to enhance resource recovery, many WRRFs are also under pressure to meet strict effluent nutrient (N and P) discharge targets. While new nitrogen management strategies that do not rely on carbon are emerging, the majority of nutrient removal systems still follow a conventional, optimized nitrification-denitrification pathway that relies on biodegradable organic carbon to support denitrification. Moreover, biodegradable organic carbon is crucial for biological phosphorus removal. Years of experience have demonstrated that successful biological nutrient removal depends not only on sufficient organic substrate, but also on the right type of bioavailable carbon supplied at the appropriate location and time for optimal utilization (Wu et al, 2009; Huang et al, 2018). Our research aims to determine the best way to utilize the variety of organic-carbon rich feedstocks available in a WRRF and how fermentation can be used as a platform process to manage the logistics of biodegradable organic carbon supply and demand. To address these questions, we conducted a pilot-scale assessment of the fermentation of a blend of wastewater-derived primary sludge (PS) and waste activated sludge (RAS) from two treatment plants. Plant 1, which only performs BOD removal, has a short solid retention time (SRT) of 2 days, while Plant 2 performs biological nutrient removal (both TN and TP) and has a longer SRT of 10 days. We conducted batch fermentation experiments on different blends of RAS and PS over a two-week period to analyze biomass kinetics and the products formed during fermentation. We used the SUMO simulator software to model each batch experiment, calibrate the two-week experimental data, and analyze the hydrolysis rates and influent fractionation variations based on the feedstock characteristics. Material and Methods Experimental Set-up Pilot-scale fermentation experiments were performed using a purpose built two-tank pilot system (Figure 1). Each bioreactor have a capacity of 75 L (20 gal). The temperature was controlled at 20 degrees C in each bioreactor. Each fermentation experiment was run in duplicate for 14 days. Three blend scenarios of RAS and PS were targeted, for both Plant 1 and Plant 2 feedstocks: 1)RAS only 2)50% RAS and 50% PS in VSS mass 3)100% PS Modelling Data from each batch experiment were modelled using Sumo Dynamita to validate the observed results as well as elucidate the biological processes. Full plant models were configured for Plant 1 and Plant 2 (see Figure 2) and an SBR process unit was used to represent the pilot reactor. Default influent parameters and fractionation for the full plant models were initially used and were tuned in order to match the TCOD, TSS, VSS, sCOD, NHx and OP data. After the initial conditions were matched, the kinetics and biology were calibrated until the experimental curves were fitted. The reduction factor of anaerobic hydrolysis was also tuned from the 0.5 default to the 0.05-0.15 range, as observed in the Water Research Foundation 4975 report. Results and Discussion Figure 3 shows the timeseries of the soluble COD yield, expressed as mass of sCOD produced per unit mass of VSS (mgCOD/gVSS) throughout the experiment for the different RAS and PS blends, for both short SRT combinations (left) and long SRT combinations (right). For each test, the experimental data was simulated on SUMO and the results of the calibrated models are shown in the dashed line. It can be noticed that the sCOD yield is different between the different PS and RAS blend combinations and also between the long and short SRT RAS. Overall, the highest fermentation rate is achieved around 3 days from the start of the experiment for all the tests. Higher sCOD yields are shown in the first week, while the sCOD production largely slows down in the second week of the test. Figure 4, left) shows the 3-day fermentation rate comparison for the different RAS and PS blends, for both short SRT and long SRT RAS biomass. The reduction factor of the anaerobic hydrolysis kinetic parameter was calibrated for each test and varied between the different feedstock blends (Figure 4, right), showing higher hydrolysis rates with higher fermentation rates and higher PS content, as reported by Ozyildiz et al 2023. The average 3 day fermentation rates ranged from 0.25+/-0.1 mg sCOD/gVSS/h for long RAS only to 3.1+/-0.2 mg sCOD/gVSS/h for 50% PS and 50% RAS, long SRT. Overall, the 50/50 ratio was noticed to be the optimum ratio to maximize soluble COD production, with both RAS types, however a higher fermentation rate (around 50% higher) was achieved when longer SRT RAS was combined with PS compared to the short SRT/PS blends. The fermentation performance is driven by the ratio between the concentration of hydrolysing microorganisms, mainly deriving from RAS, and the fermentable substrate, which is more available in primary sludge. Our research outcomes will be of value to utilities aiming to integrate the stringent effluent nutrient (N and P) discharge targets with energy and resource

The main objective of this pilot fermentation testing was to evaluate the most effective utilization of the range of organic-carbon rich feedstocks within a water resource recovery facility (WRRF). Experimental results suggest that a 50-50 blend of primary sludge (PS) and return activate sludge (RAS) fermentation leads to highest sCOD yield. The experiments were modelled using SUMO by calibrating the hydrolysis rate, plant influent fractionation, and the hydrogen production yield.

SpeakerCecconi, Francesca

Presentation time

16:30:00

17:00:00

Session time

15:30:00

17:00:00

SessionEBPR Pulse: Current Trends, Full-Scale Optimization, Model for Sustainability

Session number227

Session locationRoom 243

TopicAdvanced Level, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Cecconi, Francesca, Pifer, Leah, Bhattarai, Bishav, Downing, Leon

Author(s)F. Cecconi1, L. Pifer1, B. Bhattarai1, L.S. Downing2

Author affiliation(s)1Black & Veatch, CA, 1, 2Black and Veatch, WI

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159568

Volume / Issue

Content sourceWEFTEC

Word count14

Description: Rethinking The Impact of PFAS Emissions in Biosolids Thermal Processes through a...

Rethinking The Impact of PFAS Emissions in Biosolids Thermal Processes through a Holistic Life Cycle Assessment

Abstract

INTRODUCTION/BACKGROUND Land application of biosolids provides benefits via recycling nutrients and carbon to soil. However, Per- and polyfluoroalkyl substances (PFAS) are becoming a main hindrance to land application of biosolids with increasingly stringent regulations (McNamara, 2023). PFAS are found ubiquitously in many industrial and consumer products due to their unique chemical properties. These same properties also make them highly persistent and potentially toxic to ecosystems and humans (Holmquist, 2020). New restrictions around land application coupled with a reduction in potential landfill sites for biosolids has led many WRRFs to investigate thermal processes for biosolids management (Winchell, 2022). Incineration provides the benefit of reducing residual solids loads to be managed. Pyrolysis and gasification are emerging thermal process alternatives that also reduce residual solids loads. Moreover, these two processes offer benefits of lower concerns for exhaust gas emissions and the ability to sequester carbon in the solid residuals (Winchell, 2022). Of particular interest now to WRRFs is that these thermal processes can remove and/or transform PFAS (Winchell, 2022; McNamara, 2023). While PFAS are part of the biosolids management decision tree, they are not the only important thing. Any process implemented today still needs to make sense in two decades even if PFAS are no longer a primary concern. Additionally, the relative importance of PFAS in light of other critical environmental concerns like global warming and eutrophication have not been widely studied. While facing a seemingly pivotal moment in biosolids management history, it is critical to understand management options and the relative importance of PFAS. For this research we combined PFAS fate data from our own experiments and from literature through thermal processes. These results were then included in the LCA as their own impact category and as an input to toxicity. To the knowledge of the authors, this is the first LCA on solids handling alternatives to date that has incorporated PFAS toxicity in this way and compared impacts to conventional LCA components. In short, LCA was used to compare thermal drying, incineration, pyrolysis, and gasification holistically with regards to their impacts on humans and the environment. APPROACH PFAS Fate Through Thermal Processes Lab-scale pyrolysis and gasification experiments were conducted as part of WRF Project 5211. Targeted analysis of PFAS was completed by Eurofins on influent biosolids and effluent solids (char), liquid (py-liquid), and gas (py-gas or gasification gas). These data were used to assess removal and release of PFAS in the effluent phases. Incineration data from Winchell, 2023 was used for incineration PFAS removal performance as a reference scenario. LCA Structure 1)Five biosolids treatment scenarios for a 'typical' WRRF were compared, distinguishing between different thermal processes: thermal drying only, pyrolysis at low (500 degrees C) and high temperature (800 degrees C), gasification, and incineration. See Table 1 for a description of each scenario's treatment train. 2)Mass and energy balances across the treatment trains for each scenario were conducted, as well as a global warming potential (GWP) evaluation, using the BEAM*2022 tool (NEBRA et al., 2022). 3)PFAS emissions were first characterized alone in an impact category called 'PFAS potential,' representing total mass of PFAS emitted in each scenario as fluoride equivalents. 4)PFAS emissions were then also characterized within the toxicity impact category using the modified USEtox PFAS framework from Holmquist et. al. 2020. 5)These results were than used as an input to the LCA to compare the five thermal process scenarios with five main impact categories: i) GWP, ii) eutrophication potential, iii) freshwater ecotoxicity potential, iv) human cancerous and noncancerous toxicity potential, v) and PFAS potential. RESULTS/DISCUSSION Global Warming Comparison The incineration scenario had the highest GWP, driven mainly by scope 1 emissions (Figure 1). The scenarios with a fertilizer offset credit applied had negative scope 3 emissions. This was particularly significant for thermal drying only, because the biosolids had the highest nitrogen content, which largely drove the GWP fertilizer credit. The pyrolysis scenarios were determined to have the lowest GWPs, largely driven by lower scope 1 emissions through carbon sequestration credits achieved by the stability of the biochar product. Eutrophication Comparison The thermal drying only scenario had the highest eutrophication impact, driven by the increased hauling of the wet biosolid compared to other scenarios (Figure 2). All land applied scenarios had a beneficial fertilizer offset credit as well. This credit was largely similar between these scenarios, as the phosphorus content of the solid drove eutrophication impact for fertilizer credit and was assumed to be similar between scenarios. The lowest eutrophication potential was in the pyrolysis scenario. Toxicity Comparison Little difference was observed in freshwater ecotoxicity and human cancerous toxicity, largely due to the dominance of heavy metals, making up at least 99.5% and 96.2% in these two categories across scenarios. Heavy metal loads in the end product were assumed to be similar across all thermal processes, as only a small portion of the heavy metals would volatize, and the majority would remain in the solid residuals. In terms of PFAS potential, pyrolysis did not appear to remove much PFAS, but instead transform them into different PFAS species. Incineration and gasification were the lowest in PFAS potential, due to their high PFAS removal performance. This led also to lower human noncancerous toxicity potentials (Figure 3). Overall, heavy metals had the highest impact in human noncancerous toxicity for each scenario, but PFAS were still impactful. It should be noted that two effect factors were presented for noncancerous toxicity in Holmquist's modified USETOX model (based on epidemiological vs. rodent data). To be conservative, the higher of the two was used. Relative Impacts of Inputs Figure 4 shows the relative contribution of each input to the relevant impact categories, focusing on the thermal drying only scenario for simplicity. Most notably, it can be seen that the impact of heavy metals makes up between 93.2-99.5% of each toxicity potential category for thermal drying only. PFAS emissions comparatively only made up to 6.7% of the toxicity emissions (for human noncancerous toxicity). Eutrophication is mainly impacted by electricity use, while GWP is mainly impacted by scope 1 emissions. The PFAS potential impact category was not shown in the figure. This is because there is only one input to the PFAS potential broken up by the effluent phase the PFAS are emitted to in each scenario. CONCLUSION/SIGNIFICANCE This analysis highlights the importance of PFAS when taken into context with other known and regulated toxicants in biosolids such as heavy metals. Heavy metals made up at least 99.5% and 96.2% of freshwater ecotoxicity and human cancerous toxicity impacts across all scenarios. Even when a conservative assumption for PFAS toxicity was used for human noncancerous toxicity, heavy metals made up the largest portion of this impact as well. This analysis also highlights two biosolids alternatives, gasification and pyrolysis. Gasification was observed to be a relatively low impact alternative in most of the LCA categories that also safeguards against uncertainty around PFAS toxicity and future regulations in biosolids. This option provides not just transformation, but potentially good removal of PFAS species. Pyrolysis however was observed to be the best option in this analysis when considering the relatively low impact of PFAS on the toxicity potential impact categories, and that pyrolysis had the lowest impact in the other critical LCA impart categories. The key impact of this work is the reframing of PFAS as not the only consideration, but one of many aspects to be included for holistic biosolids management.

This paper was presented at the WEF Residuals & Biosolids and Innovations in Treatment Technology Joint Conference, May 6-9, 2025.

SpeakerPifer, Leah

Presentation time

08:50:00

09:10:00

Session time

08:30:00

11:45:00

SessionSome Like It Hot - Diving into Incineration, Pyrolysis, and Gasification

Session number13

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAdvanced Thermal Conversion, Biochar, Energy and Carbon Neutrality, Energy Conservation/Management, Energy recovery, Gasification, Greenhouse Gases, incineration, Intensification, Knowledge Transfer, PFAS, PFAS/Emerging Contaminants, pyrolysis, Regulatory Requirements, Thermal Processes

Author(s)

Pifer, Leah, Cecconi, Francesca, Shankar, Sowjanya, Shaw, Andrew, Hoener, Webster, Moss, Lynne, McNamara, Patrick

Author(s)L. Pifer1, F. Cecconi1, S. Shankar1, A. Shaw1, W. Hoener1, L. Moss1, P. McNamara1

Author affiliation(s)Black & Veatch, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159797

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count17

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