McNamara, Patrick

Pat is a Wastewater Process Engineer with Black Veatch and an associate professor at Marquette University. He has been researching biosolids pyrolysis for 10 years. His research group has conducted studies on the energy costs of biosolids pyrolysis, removal of pollutants during pyrolysis, and the use of biochar as a soil amendment and adsorbent. He currently has a patent pending related to using biosolids-derived biochar as a catalyst for pyrolysis. In addition he has conducted research on dewaterability issues at a number of biosolids facilities.

Titles from this speaker

Description: Cleaning Up after the Pandemic: How Old and New Quaternary Ammonium Compounds Affect...

Cleaning Up after the Pandemic: How Old and New Quaternary Ammonium Compounds Affect Anaerobic Digestion

Abstract

Summary of Abstract Quaternary ammonium compounds (QACs) have been widely used as disinfectants. The COVID-19 pandemic led to a rise in the usage of QACs, which has increased the load to wastewater treatment plants. QACs partition to solids and therefore enter anaerobic digesters. The objective of this research was to understand how QACs, which are designed to inhibit microbes, impact the biological process of anaerobic digestion. Specifically, different chemical classes were studied, including the widely used and widely studied benzylalkyldimethylammonium compounds (BACs) and the more recently used, but less studied, ethylbenzylalkyldimethylammonium compounds (EtBACs). Both short-term anaerobic toxicity assays and long-term chronic exposure experiments were conducted. Results revealed that the acute and chronic toxicity of QACs are closely related to their core chemical structure. The toxicity of QACs decreased with the growth of their alkyl chain. Meanwhile, dialkyldimethylammonium compounds (DADMACs) were more toxic than BACs at the same effective concentration. Additional experiments revealed that anaerobic digesters were more susceptible to functional collapse (i.e., biogas production and volatile solids reduction decrease) by other inhibitors after exposure to QACs. Volatile fatty acid profiles provided insights into the mechanisms of inhibition. Finally, QACs were removed from the feed to chronically exposed anaerobic digesters to elucidate the reversibility of decreased functional performance. This is the first research reported to comprehensively investigate the role of EtBACs along with BACs and DADMACs on anaerobic digestion. 1. Background, Originality and Status of Subject Quaternary ammonium compounds (QACs) have been used for decades as antimicrobials and preservatives as well as for other functions in personal care products and consumer goods (Figure 1).1 Especially during the SARS-CoV-2 pandemic, the usage of QACs increased dramatically as the predominant ingredients in disinfecting products to limit disease transmission.2 Currently over 200 disinfectants recommended by the US Environmental Protection Agency for use against COVID-19 contain QACs. The global QACs market was valued at $963.7 million in 2019, and it is expected to grow at a rate of 6.8% and reach $1.63 billion by 2027 due to increased demand for disinfectant products from hospitals, clinics, the food industry, and households.3 Thus, it should be anticipated that the amounts of QACs used and released into the environment will increase. Approximately 75% of QACs used enter into sewers and consequently water resource recovery facilities (WRRFs).4 The majority of QACs in influent wastewater adsorb to sludge and are then transferred to solids handling processes, such as anaerobic digestion (AD), where QACs levels are as high as 500 mg/kg (dry weight).1 AD is a critical biological treatment technology for solids stabilization and energy recovery. Different types of bacteria and archaea work together to carry out sequential tasks including hydrolysis, acidogenesis, acetogenesis, and methanogenesis. However, precisely because anaerobic digestion is highly dependent on the synergistic action of multiple microorganisms, it is more sensitive to toxic substances than aerobic treatment. QACs are a class of organic, cationic chemicals that contain one or more positively charged quaternary amine groups and at least one hydrophobic alkyl chain. The most commonly used and studied groups of QACs are mono-cationic compounds including benzyl alkyl dimethyl ammonium compounds (BACs, also known as benzalkonium compounds), dialkyl dimethyl ammonium compounds (DADMACs), and alkyl trimethyl ammonium compounds (ATMACs) (Fig. 1). Additionally, ethyl benzyl ammonium compounds (EtBACs) usage has been increasing in recent years.5-7 Because QACs are designed to inhibit microorganisms,8 it is expected that QACs could adversely affect the performance of AD. However, it remains unknown how the chemical core structure of QACs (i.e. the chemical group of QACs) is linked to acute and chronic impacts on AD performance. It is important to understand the potential impacts of QAC groups, concentration, and exposure time to AD function and microbial community, as well understand if these impacts are reversible following removal of QACs from a system. Overall, as the amount, and types, of QACs in consumer usage continues to grow, so too must our understanding of environmental impacts. In this study, we evaluated the acute toxicity of ten different structural QACs and conducted chronic exposure experiments on eight of these QACs commonly found in wastewater. 2. Presentation Objectives The overall objective of this presentation is to present findings from the acute and chronic QAC exposure experiments using lab-scale anaerobic digesters. The first specific objective will be to present the acute exposure toxicity of 10 commonly used QACs with various chemical structures. IC50 results will be reported and correlated to chemical structure. The second objective is to reveal the impact of QACs on methane production and volatile fatty acid profiles. The third objective is to reveal the reversibility of these impacts. Lab results for the first two objectives are completed. Lab results for the reversibility objective will be completed by February 2024. 3. Approach, Key Results, and Discussion Anaerobic toxicity assay style testing was performed to determine inhibitory concentrations (acute toxicity) of the different QACs to methane production. In addition, 60 digesters (triplicate sets of each group) with different QACs amendment including individual QACs and mixed QACs were operated simultaneously to assess the impact of chronic exposure. To monitor functional health, biogas and pH were measured daily. Meanwhile, methane and volatile fatty acids (VFA) were measured weekly; total solids (TS) and volatile solids (VS) were measured every solids retention time (SRT). The chronic exposure experiments are set to last approximately 25 SRT values (375 days). The results of the short-term ATAs indicated that the toxicity of QACs varies by their core structure (Figure 2a). For the same class of QACs, the toxicity decreases as the alkyl chain length increases. Meanwhile, exposure to a group of mixed QACs had synergistic effects. Compared with BAC, DADMAC is more toxic to anaerobic digestion at the same effective concentration (Figure 2b). High level QACs exposure caused VFAs to accumulate (Figure 3), indicating that methanogens were more sensitive to QACs compared to acidogens/acetogens. The results from the chronic QAC exposure experiments revealed that exposure to low level (60 mg/kg TS) QACs did not inhibit the performance of anaerobic digestion (Figure 4), and the effect were not affected by the chemical structure of the QAC or the duration of exposure. However, low level QACs exposure significantly altered the functional stability of the anaerobic digester after exposure to other potential inhibitors such as ammonia, Benzethonium chloride, and Rumensin (Figure 5). With the exposure concentration gradually increasing, QACs with short hydrophobic alkyl chain (like C8DADMAC and C12BAC) first started to inhibit methane production. Accumulation of VFAs led to a rapid decrease in pH, which further inhibited the activity of methanogens, and eventually the anaerobic digester was completely disabled under the combined stress of QAC and low pH (Figure 6). Interestingly, during the chronic amendment of QAC, one lab-scale anaerobic digester became more tolerant to QAC and maintained normal function even when the exposure concentration was gradually increased above IC50. The functional health under high level QACs chronic exposure is being continuously monitored and the experiment will end in February, 2024. Finally, the reversibility of QACs' impacts will be assessed. These results will be generated prior to the conference. At the time of the conference, we will be able to conclude how old (BACs, DADMACs), and new (EtBACs) QACs affect anaerobic digestion performance. Broader Impacts and Environment Significance This study will connect acute/ chronic exposure simulation experiments to test the comprehensive effect and reversibility of a more realistic scenario of gradually loading QACs with different core structures on the performance of anaerobic digester. The findings of this study will contribute to advancing broader understanding on why process performance is affected based on the type of QACs in a particular wastewater stream. This work will provide guidance on potential environmental impacts and information on how to balance use recommendations with improvements in WRRFs such that health and environmental protection are balanced

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerLu, Zihao

Presentation time

11:15:00

11:45:00

Session time

10:45:00

11:45:00

SessionResearch and Innovation

Session number01

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicAnaerobic Digestion, Quarternay Ammonia Compounds, Research

Author(s)

Lu, Zihao

Author(s)Z. Lu1, D. Zitomer1, C. Marshall1, A. Mahony1, W. Arnold2 P. McNamara1, 3

Author affiliation(s)Marquette University 1; Marquette University1; Marquette University 1; University of MN 2; University of MN 2; Black & Veatch3;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159454

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count16

Description: Should Pyrolysis Be Employed To Remove PFAS and Microconstituents from Biosolids?...

Should Pyrolysis Be Employed To Remove PFAS and Microconstituents from Biosolids? Experimental Results and Practical Considerations

Abstract

Introduction Per- and Polyfluoroalkyl Substances (PFAS) have been an increasing focus of the public, legislative bodies, and the regulatory community, and recent EPA activities highlight this focus with respect to biosolids(1). In October 2021 the EPA released its PFAS Strategic Roadmap, outlining EPA actions with respect to PFAS for 2021-2024: these activities include a risk assessment of PFAS in biosolids to be completed by 2024(1). EPA also announced its intent to pursue the classification of PFAS under the Resource Conservation and Recovery Act (RCRA). While it is no means certain that federal PFAS regulations for biosolids are forthcoming, some utilities have faced - or might face - increasing pressure to consider either i) reducing PFAS and microconstituent loads in biosolids, or ii) processes that provide an alternative product for land application. Conventional treatment processes such as anaerobic digestion or composting do not mitigate PFAS concentrations(2). Pyrolysis is an alternative solids process that is gaining interest as a possible approach to mitigate PFAS and microconstituents. Current literature is contradictory on the impact of pyrolysis on PFAS, with removal(3) and no removal(4) being reported. Thus, new experiments were conducted to determine the fate of PFAS during pyrolysis of biosolids, and results will be presented at the conference. In addition to knowing the impacts of pyrolysis on the fate of PFAS, practical considerations of pyrolysis such as generation of difficult-to-handle byproducts and side streams, dryer operations and costs, and product management need to be evaluated holistically. To approach this topic of PFAS removal via pyrolysis holistically, this presentation has three main objectives: 1. Define pyrolysis and the pyrolysis products generated from municipal biosolids 2. Determine the impact of pyrolysis on microconstituents, including PFAS, using novel, unpublished pyrolysis batch studies that investigate the fate of PFAS in biochar, pyrolysis-liquid, and pyrolysis-gas 3. Understand practical considerations for implementation of pyrolysis Objective 1: Define pyrolysis and pyrolysis products Pyrolysis is a thermal decomposition process that occurs at high temperatures (normally over 450ºC) under limited or no oxygen. Pyrolysis of biosolids generates solid, liquid, and gaseous products. The solid product, called biochar, is a carbon-rich product similar to charcoal that can be used as a soil amendment because it retains moisture(5). It can also adsorb nutrients from thickening filtrate and be used to improve grass growth(6). The non-condensable gases produced, called py-gas, contain energy rich constituents such as methane and hydrogen(7). The pyrolysis liquid can be composed of two phases: light non aqueous phase called bio-oil and an aqueous phase known as aqueous pyrolysis liquid (APL). The bio-oil, which can be used as a renewable fuel upon upgrading, is corrosive during combustion and difficult to handle, whereas the APL also contains organic compounds and sometimes high concentrations of ammonia that can be toxic to biological processes such as anaerobic digestion(8). Objective 2: Determine the impact of pyrolysis on PFAS and microconstituents Novel Research Approach Experiments will be conducted in a lab-scale batch pyrolysis system as described elsewhere(9). Dried municipal biosolids will be used as the influent feed, and effluent biochar, pyrolysis-liquid, and pyrolysis gas samples will be collected for PFAS analysis. In total, 37 PFAS compounds will be analyzed by PACE Analytical® in the solid, liquid, and gas phases to determine the impact of pyrolysis on the removal of PFAS from biosolids. These experiments will be completed by the end of 2021 and the analysis will be completed by March 2022. This experiment will be the first study to investigate the presence of PFAS in all three product phases (solid, liquid, gas) following pyrolysis. Results from Previous Lab-Scale Studies These results will be presented in light of Dr. McNamara's previously published data that found 3 possible fates of microconstituents during pyrolysis of biosolids: a. No removal: microconstituents reside with solids (e.g. metals) b. Volatilization: microconstituents leave solids and reside with pyrolysis liquid c. Transformation: microconstituents are chemically transformed Batch pyrolysis experiments revealed that pyrolysis removed triclocarban (Figure 1), triclosan, and nonylphenol from biosolids(10). Triclosan and nonylphenol volatilized away from the biochar and into the pyrolysis liquid; triclocarban was chemically transformed during pyrolysis. These results indicate that, while pyrolysis might likely remove PFAS from the solid biochar phase, PFAS might still likely reside with pyrolysis liquid requiring further downstream processing. The experiments and analysis to be completed by March, 2022 will confirm this hypothesis. Objective 3: Practical considerations for implementation of pyrolysis Pyrolysis has been extensively used for non-biosolids feedstocks but is not yet mainstream for biosolids applications, partly because of the overall operational complexity of these systems and cost considerations. Compared to biosolids land application, pyrolysis technologies represent a significantly higher capital investment for utilities since feed to pyrolysis must contain only 5 to 15% moisture, requiring thermal drying as a pre-requisite for pyrolysis. The capital and operational costs for drying could be very high depending on the moisture content of the influent biosolids(7). Including drying within the system boundary also makes the overall energy balance of a pyrolysis system less favorable. The energy available in pyrolysis gas and liquid products is approximately equal to the energy required for drying and pyrolysis of biosolids that are 20% solids. Based on anecdotal evidence from some of the demonstration facilities, phase-separation, i.e., separating the various pyrolysis products, downstream from the pyrolysis reactor can also be a challenge that could impact the quality of pyrolysis products for downstream applications. The bio-oil that is produced can be difficult to handle and potentially hazardous. To address the handling concerns with bio-oil, pyrolysis systems either need to run hot enough to not produce bio-oil or utilities need other plans for handling bio-oil post production. In short, while a potentially promising method for biosolids treatment, long-term operational viability of these systems for biosolids applications, sidestream characteristics, and emissions control requirements for these systems are yet to be proven. The potential benefits of pyrolysis include solids destruction resulting in less hauling costs, generation of pyrolysis-gas that could be co-combusted with digester gas or landfill gas, and generation of biochar which has potential as a value-added product and the potential to reduce PFAS. Biochar improves the soil characteristics by not breaking down readily, providing carbon sequestration and improving moisture-holding capacity of soils. Utilities considering pyrolysis have to weigh the potential benefits of the technology alongside costs and other operational considerations to determine the overall feasibility of the technology for full-scale implementation. Any government subsidies or credits to support PFAS removal, that might make pyrolysis more affordable to utilities, will also be reviewed and presented in this paper.

This paper was presented at the WEF Residuals and Biosolids Conference in Columbus, Ohio, May 24-27, 2022.

SpeakerMcNamara, Patrick

Presentation time

14:00:00

14:30:00

Session time

13:30:00

17:00:00

Session number03

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicLand Application, PFAS/Emerging Contaminants, pyrolysis

Author(s)

P. McNamara

Author(s)P. McNamara1; H. SANTHA2; L. Moss3; Z. Liu4

Author affiliation(s)Residuals and Biosolids Speaker; 1Black & Veatch; 2Residuals and Biosolids Speaker; 3California State University - Bakersfield; 4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2022

DOI10.2175/193864718825158431

Volume / Issue

Content sourceResiduals and Biosolids

Word count17