Fairley-Wax, Madeleine

Madeleine Fairley-Wax was a speaker at the WEFTEC 2025 conference held in Chicago, IL from September 27-October 1.

Titles from this speaker

Description: Enhancing Anaerobic Digestion with MHP

Abstract

Introduction The Microbial Hydrolysis Process (MHP), developed to enhance anaerobic digestion (AD) performance, uses the hyper-thermophilic bacterium Caldicellulosiruptor bescii (C. bescii) in a post-digestion hydrolysis process. Unlike pre-digestion methods (Hansen et al, 2021), MHP feeds AD digestate to a 75°C hydrolysis tank populated with C. bescii for a hydraulic retention time of two days (Parry et al. 2022). Here, C. bescii and its enzymes hydrolyse cellulose and complex carbohydrates and convert them to volatile fatty acids (VFAs) in an anaerobic, neutral-pH reactor. The VFAs are then returned to the AD, where methanogens convert them into biogas. Figure 1 illustrates the microbial activity AD with MHP. The performance of AD with MHP has been tested at lab- and pilot-scale with consistent results; the addition of MHP increases volatile solids reduction (VSR) to greater than 75%. Figure 2 shows the results of MHP studies on solids from 4 different water resource recovery facilities (WRRFs) with well-performing existing AD systems. Encouraged by pilot results, VandCenter Syd (VCS) in Denmark is now designing MHP implementation at its Ejby MÃ¸lle WRRF, and conceptual and preliminary designs have been developed for several WRRFs in the US. An ongoing pilot at North Davis Sewer District (NDSD) in Syracuse, UT has operated at steady-state since July 2024. Data from this pilot and prior studies are used to refine a process model (Sumo) to predict AD performance with MHP based on feed characteristics. The results of the pilot study, the model and preliminary design, and analytical results for pathogens, microbial populations, sludge dewaterability, and sludge characterization will be presented. Material and Methods AD with MHP has been studied using solids from several facilities at both lab and pilot scales. Most recently, pilot-scale testing has been conducted at North Davis Sewer District in Syracuse, UT. The pilot-scale system consists two 325-gallon anaerobic digesters and one 140-gallon MHP reactor. Pictures of the pilot trailer located at NDSD and the pilot trailer process room are shown in Figure 3. The NDSD pilot system is operated to simulate proposed process changes to achieve Class A biosolids, boost VSR, and increase biogas production, using a staged AD with batch intermediate MHP and heat recovery. A simplified process flow diagram of the pilot MHP system is presented in Figure 4 and a process flow diagram of the proposed full-scale system with heat recovery is presented in Figure 5. Pilot Anaerobic Digester 1 (AD1) was fed digested sludge once per day from the full-scale digested sludge transfer pumps. Sludge from AD1 was automatically fed 4 times per day to the MHP tank, and hydrolysed sludge from the MHP tank was fed 4 times per day to Pilot Anaerobic Digester 2 (AD2). Characteristics of the full-scale system feed and digestate as well as the contents of AD1, the MHP tank, and AD2 were measured using standard methods. Routine analyses to monitor performance and stability include volatile and total solids, total acids, alkalinity, and pH, while additional sludge analysis assesses pathogen reduction, microbial populations, sludge dewaterability, carbohydrate composition, and VFA fractionation. The VSR of the digestion process with MHP, calculated using the volatile and total solids measurements, was the key indicator of performance. Results of this pilot study are used to calibrate a process (Sumo) model to predict digestion performance for facilities with different feed characteristics and will be discussed in the final paper. Findings Previous studies have proven significant improvement in digester performance with the addition of MHP, as indicated by the increase in VSR to 75 and higher. These findings were corroborated by the results of the pilot at NDSD, shown in Figure 6. The existing AD system at NDSD achieves 63.8 percent VSR on average, and the addition of MHP improved performance to 75 percent once steady state was achieved. Table 1 presents the comparison the proposed staged AD with batch intermediate MHP to baseline AD performance. The increased VSR and improved dewaterability result in a 38% decrease in wet tons of biosolids produced per year, and an estimated 18% increase in biogas production assuming the biogas yield is unchanged. Further, laboratory analyses confirm that batch MHP reduces the concentration of fecal coliform below detectable levels, meeting the EPA criteria for pathogen reduction in Class A biosolids. The operational data and results of routine analyses, microbial population analysis, and sludge characterization from the pilot study at NDSD have informed the continued development of a model to simulate the impact of MHP based on influent sludge characterization. With this model, performance of AD with MHP at other facilities can be predicted. Significance MHP represents a significant advancement in AD technology and offers the highest achievable VSR for municipal WRRF AD systems to date. By allowing the digestion of cellulose and other recalcitrant organics, MHP maximizes AD efficiency, thus increasing biogas yield and reducing biosolid production. These improvements result in substantial cost savings on biosolids management -- a major interest for WRRFs. These benefits position MHP as a scalable, innovative solution to enhance AD performance globally.

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

SpeakerFairley-Wax, Madeleine

Presentation time

09:30:00

09:50:00

Session time

08:30:00

11:45:00

SessionInnovations in Sludge Management: Enhancing Anaerobic Digestion and Phosphorus Control

Session number10

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAerobic Digestion, Anaerobic Digestion, Biogas Utilization, Biosolids, Biosolids treatment, Class A, Dewaterability, Phosphorus recovery, struvite, electrochemical, Pilot Scale, Process Intensification, Resource Recovery, Solids Pre-Treatment, Sustainability, thermophilic, THP, CAMBI

Author(s)

Fairley-Wax, Madeleine, Cope, Stephanie, Parry, David

Author(s)M. Fairley-Wax1, S. Cope1, D. Parry1

Author affiliation(s)Jacobs, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159783

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count6

Full-Scale Enhancement of Anaerobic Digestion with the Microbial Hydrolysis Process

Abstract

INTRODUCTION
The Microbial Hydrolysis Process (MHP) using Caldicellulosiruptor bescii (CB) enhances anaerobic digestion (AD) by increasing volatile solids reduction (VSR) and biogas production. Unlike pre-digestion hydrolysis, MHP feeds digestate to a 75°C tank populated with CB (Parry et al. 2022). This process has a retention time of two days and hydrolyzes complex carbohydrates to volatile acids (VAs), which are then fed back into AD systems, where methanogens convert them into biogas. Figure 1 illustrates the microbial activity in AD with MHP.

MHP with AD has been studied at laboratory and pilot scale with solids from four different water resource recovery facilities (WRRFs) with consistent results: increased VSR, increased biogas production, and higher cake solids in the final product. Encouraged by these results, VandCenter Syd (VCS) in Denmark is now designing a full-scale MHP system at its Ejby Mølle WRRF, and preliminary designs have been developed for several WRRFs in the US.

Data from an ongoing pilot at North Davis Sewer District (NDSD) in Syracuse, Utah and prior studies are used to refine a predictive MHP process model (SUMO) to inform full-scale MHP designs based on sludge feed characteristics. The pilot study results, model outcomes, and analytical results for pathogens, microbial populations, dewaterability, and sludge characterization will be presented.

METHODOLOGY AD with MHP has been tested in laboratory- and pilot-scale AD systems with solids from several US WRRFs. Early studies integrated MHP on the sludge recirculation line for mesophilic AD systems to increase VSR and biogas production. The ongoing pilot study at NDSD, which began in May 2024 and reached steady state in July 2024, uses a two-stage mesophilic AD system with intermediate batch MHP to produce Class A biosolids in addition to increasing VSR and biogas production. Figure 2 shows pictures of the pilot trailer at NDSD.

Characteristics of the raw and digested sludge from the NDSD full-scale system and sludge from the pilot AD tanks and MHP reactor were measured using standard methods. Routine analysis to monitor performance and stability include VS, total solids (TS), total acids, alkalinity, and pH. Additional analyses included fecal coliform, microbial communities, rheology and dewaterability, carbohydrate composition, and VA fractionation. VSR was the key indicator of performance.

Using data from this pilot and previous studies, the Jacobs team is developing an improved SUMO process model to predict the effects of MHP. To refine assumptions and address unknown variables in the model, additional lab-scale experiments will provide pertinent data that has not yet been captured, such as total suspended solids, volatile suspended solids, soluble chemical oxygen demand, and MHP process gas production and quality.

RESULTS AND DISCUSSION The addition of MHP to AD systems significantly improved performance in all trials, increasing VSR from a baseline of 58 to 64% to over 75% in all studies (Parry et al. 2023, 2024). Figure 3 summarizes the results from four studies, and Figure 4 NDSD pilot VSR data.

The improvement is VSR primarily attributed to the hydrolysis of recalcitrant organics, such as cellulose and complex carbohydrates or polysaccharides, in the MHP reactor. This is supported by the rise in VA concentrations from 500 mg/L upstream of the MHP reactor to 1500 mg/L in the MHP reactor. VA concentration MHP during the NDSD study are presented in Figure 5.

Preliminary analysis of the VA profile revealed that acetic acid (50%) and propanoic acid (10%) were the dominant acids present, with remaining 40% of the total acids likely consisting of lactic acid. Pathogen reduction was significant, with non-detectable levels of fecal coliform following MHP treatment. Dewatering performance showed increased dewaterability, although increased polymer demand was required due to higher soluble COD concentrations. Further, Further analyses of microbial populations, sludge rheology, and other performance indicators are ongoing to better understand the long-term stability and effectiveness of the MHP process and will be presented in the final paper. The SUMO model will include the key physical and biological processes of AD with MHP, shown in Figure 6, including hydrolysis due to increased temperature and the enzymatic and metabolic pathways and products CB.

The model will also predict how different anaerobic organisms such as acidogens, acetogens, and methanogens grow in the anaerobic process because of CB's metabolic products such as acetate, lactate, and propionate. Results from the model development, as well as updates to previously presented designs for VCS and NDSD, will be shared during WEFTEC 2025.

SIGNIFICANCE
Jacobs' MHP technology has demonstrated significant improvements to anaerobic digestion, offering the highest achievable VSR for municipal WRRF AD systems to date while also reducing pathogen levels and improving dewaterability. The development of the SUMO process model is integral to further developing the technology and provides a valuable tool for predicting and optimizing MHP performance. This results in substantial cost savings on biosolids management — a major interest for WRRFs. Further, the predictive process model will inform the design and operation of MHP systems at other WRRFs, leading to cost savings in design and improved process performance.

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

Presentation time

09:30:00

10:00:00

Session time

08:30:00

10:00:00

SessionPass the Gas: Digester Rehab, Intensification, and Innovation

Session locationMcCormick Place, Chicago, Illinois, USA

TopicBiosolids & Residuals

Author(s)

Fairley-Wax, Madeleine, Cope, Stephanie, Ohemeng-Ntiamoah, Juliet, Nielsen, Per, Hatch, David, Parry, David