Parry, David

Dr. David L. Parry, PE, BCEE has 44 years of experience and a global reputation for providing sustainable solutions to recover resources from...

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About Parry, David

Dr. David L. Parry, PE, BCEE has 44 years of experience and a global reputation for providing sustainable solutions to recover resources from wastewater. He earned his bachelor's and master's degrees in mechanical engineering from BYU and his Ph.D. from the University of Illinois at Urbana-Champaign. Dr. Parry is a registered mechanical and civil engineer in several states and provinces. He is vice president and senior fellow at Jacobs and their leading anaerobic digestion expert. Dr. Parry is a patent holder and inventor of methods to enhance anaerobic digestion with the microbial hydrolysis process to convert cellulose into biogas.

Parry, David

Titles from this speaker

Achieving Class A Biosolids with Staged Thermophilic Anaerobic Digestion

Abstract

INTRODUCTION: The Metropolitan Sewer District of the Greater Cincinnati (MSDGC) owns and operates the Little Miami Wastewater Treatment Plant (LMWWTP). Figure 1 is an aerial view of the LMWWTP. The LMWWTP has annual average capacity of 27 mgd with a design peak wet weather capacity of 100 mgd. The current solids processing system dewaters raw sludge for disposal in landfill. MSDGC is in the process of designing and building a new solids processing system that will produce Class A biosolids and beneficially use the biogas from anaerobic digestion. The new solids processing system consists of sludge receiving, screening, thickening, anaerobic digestion, dewatering, biosolids storage, and truck loadout. Biogas produced from the anaerobic digesters will be treated and beneficially used to fuel hot water boilers, engine driven cogeneration units, and gas turbine driven aeration blowers. Initially, the temperature phased anaerobic digestion (TPAD) process with batch pasteurization was selected. Figure 2 is a rendering of the solids processing system with the initial TPAD process. As the design developed, the process was changed to staged thermophilic anaerobic digestion (STAD) without batch pasteurization to reduce capital costs, while still able to produce Class A pathogen reduction biosolids. Figure 3 is a solids process flow diagram with the STAD process. Changing the process from TPAD to STAD was made early in the pre-construction phase of this progressive design build (PDB) project. METHODOLOGY: Starting with the planning phase, MSDGC established a business case with the primary goal of producing Class A biosolids for beneficial use through land application. Another goal was to beneficially use all the biogas from anaerobic digestion on-site. MSDGC chose to hire a design-builder to deliver the new solids processing system using the progressive design build (PDB) method. The PDB method was selected to provide flexibility for MSDGC's input during the design and for more construction cost certainty from a guaranteed maximum price (GMP) before design is completed. Early in the design phase, the construction cost was estimated to be higher than the planning level, project budget. MSDGC worked with their design-builder to value engineer the design to reduce construction costs. One cost saving item to reduce the construction cost is by changing the digestion process from TPAD with batch pasteurization to STAD. The TPAD system was based on two 2.4 Mgal digesters in series: a thermophilic digester followed by batch pasteurization and a mesophilic digester. The STAD system is three 1.2 Mgal thermophilic digesters in series. The last digester is also serving as storage tank to dewatering. Changing from TPAD to STAD increased the number digesters but decreased the total volume from 4.8 Mgal to 3.6 Mgal. The change to STAD eliminated the need for four batch pasteurization tanks and associated mixing, pumps, and heat exchangers. Having all three digesters operate at thermophilic temperatures eliminated the need for cooling heat exchangers required with TPAD. To achieve the necessary pathogen reduction to produce Class A biosolids, the technical team applied features from several successful operations of STAD installations. Table 1 lists the similarities and differences to LMWWTP of several successful thermophilic anaerobic digestion installations. All these installations achieved Class A biosolids with mixed plug-flow digesters in series. Figure 4 shows the configuration of the three mixed, plug-flow, thermophilic digesters in series. Each of the digesters in the LMWWTP project were designed to exceed the minimum time and temperature requirements set by the biosolids regulations. Sludge stabilization and pasteurization will be achieved at the same time with STAD. A minimum retention time of one day and corresponding temperature of 55 degrees C will be exceeded under all operating conditions. Raw sludge will be fed at the top of silo-shaped tanks and withdrawn at the bottom. The feed will be heated to over 55 degrees and maintained throughout the digester. A minimum hydraulic retention time of 8 days will be achieved even with one digester out of service. When all digesters are operating, there will be triple redundancy with three-staged thermophilic digestion. When one digester is out of service, there will be redundancy with two-staged thermophilic digestion. During commissioning, the biosolids with be tested to verify Class A pathogen reduction is achieved. FINDINGS: The flexibility of the PDB method enabled the technical team to design the new solids processing system to save construction costs by changing the anaerobic digestion process from TPAD to STAD. Solids processing systems at other water resource recovery facilities have been achieving Class A biosolids with STAD. The LMWWTP STAD process is expected to produce Class A biosolids. During commissioning the necessary testing will verify the biosolids quality. SIGNIFICANCE: The STAD process offers a lower cost alternative and expected to achieve Class A biosolids. The PDB method provides flexibility for owners and engineers to design to budget.

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

SpeakerParry, David

Presentation time

16:15:00

16:45:00

Session time

15:45:00

16:45:00

SessionAnaerobic Digestion

Session number22

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicAnaerobic Digestion, Class A, thermophilic

Author(s)

Parry, David

Author(s)D. Parry1, M. Hatzigeorgiou1, J. Johnson2

Author affiliation(s)Jacobs 1; Jacobs 1; Metropolitan Sewer District of Greater Cincinnati 2;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159470

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count10

Application of the Microbial Hydrolysis Process on an Existing Anaerobic Digestion System

Abstract

Abstract Research and development of the microbial hydrolysis process (MHP) has progressed for application at existing anaerobic digestion facilities. MHP using the thermophilic, anaerobic bacterium: caldicellulosiruptor bescii (CB), has increased the volatile solids reduction (VSR) in pilot-scale anaerobic digestion systems. The increased VSR is attributed to the enzymatic activity of CB to hydrolyze cellulose into volatile fatty acids. Design of the first application of MHP is underway at VandCenter Syd's (VCS) Ejby Mølle water resource recovery facility (WRRF) in Odense, Denmark. A business case evaluation showed an attractive return on investment (ROI) based on capital expenses (CapEx) for the MHP system and savings on operating expenses (OpEx) from increased biogas production and reduced biosolids production. Introduction The Microbial Hydrolysis Process (MHP) using Caldicellulosiruptor bescii (CB), a hyper-thermophilic bacterium was developed to enhance the performance of any anaerobic digestion process. Instead of pre-digestion hydrolysis with CB (Hansen et al. 2021), post-digestion hydrolysis is used. MHP consists of feeding digestate from an anaerobic digester to a hydrolysis tank populated with CB for a hydraulic retention time of two days at 75 degrees C (Parry et al. 2022). The CB bacterium and associated enzymes hydrolyze cellulose and other volatile solids and produce volatile fatty acids (VFAs) in an anaerobic, neutral pH reactor. These VFAs are returned to the anaerobic digester where methanogens convert them into biogas. Figure 1.1 shows the microbial activity in anaerobic digesters before and after MHP. The performance of anaerobic digestion with MHP has been tested in pilot-scale digestion systems on solids from three different water resource recovery facilities (WRRFs). Results from the pilot tests demonstrated significant increases in volatile solids reduction (VSR) from around 50-60 percent without MHP to greater than 75 percent with the addition of MHP (Parry et al. 2023). MHP is a new technology that enhances the performance of any anaerobic digestion process for more biogas production and less biosolids production. Based on encouraging pilot tests at other WRRFs, VandCenter Syd (VCS) has started the design for application of MHP at their Ejby Mølle WRRF (EMWRRF) in Odense, Denmark (Nielsen et al. 2023). Material and Methods A calibrated process model was used to evaluate the mesophilic anaerobic digestion (MAD) performance at the EMWRRF with and without MHP. Since increased VSR is attributed to hydrolyzing residual cellulose, a pragmatic approach was used to predict VSR by measuring the cellulose fraction of the volatile solids. A process flow diagram of the existing MAD system is shown in Figure 1.2 with the addition of MHP. The four existing digesters are 2,800 m3 each and the new MHP tank is 1,000 m3. Results and Conclusions Based on the performance of the previous pilot tests, the expected performance of the EMWRRF with MHP is shown as compared to the current operation. Figure 1.3 shows the increased volatile solids (VS) conversion to biogas with MAD + MHP and the corresponding reduction in residual VS. A VSR of 50% for MAD and a VSR of 75% for MAD + MHP is shown. The residual VS after digestion is cut in half (from 38% to 19%) with MHP and corresponds to a 50% increase in biogas production. The additional biogas is attributed to the hydrolysis of cellulose by MHP for digestion. The results of the predicted mass and energy balance for the EMWRRF digestion facility is shown in Tables 1.1 and 1.2. Biogas will be used to fuel the existing combined heat and power (CHP) system. Increased biogas will increase the revenue to VCS from the power that is currently sold into the grid and the heat that is sold into the district heating system. A business case evaluation showed a positive return on investment (ROI) for the OpEx: revenue from the additional electricity and heat recovery, and the operating cost savings from the reduction in biosolids. The revenue and cost savings of the OpEx justified the CapEx of the MHP system for an attractive ROI. The presentation will show the business case evaluation results and overall expected performance impacts of the system.

The Microbial Hydrolysis Process (MHP) using the thermophilic anaerobic bacterium: caldicellulosiruptor bescii (CB) is applied to VandCenter Syd's (VCS) Ejby Molle Water Resource Recovery Facility (WRRF) in Odense, Denmark. Application of the MHP is expected to increase the volatile solids reduction of the existing anaerobic digestion system by hydrolyzing cellulose resulting in increased biogas production and decreased biosolids production.

SpeakerParry, David

Presentation time

15:30:00

15:50:00

Session time

15:30:00

17:00:00

SessionAdvances in Anaerobic Digestion

Session number219

Session locationRoom 344

TopicBiosolids and Residuals, Intermediate Level, Research and Innovation

Author(s)

Parry, David, Nielsen, Per, Fairley-Wax, Maddy

Author(s)D.L. Parry1, P.H. Nielsen2, M. Fairley-Wax3

Author affiliation(s)1Jacobs, UT, 2VCS Denmark, 3Jacobs, IL

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159615

Volume / Issue

Content sourceWEFTEC

Word count13

Circular Biochar Economy

Abstract

Insights on going from a linear incineration economy to a circular biochar economy are discussed from the perspective of the Edmonds, WA wastewater treatment plant (WWTP) with reference to the Silicon Valley Clean Water (SVCW) water resource recovery facility (WRRF) and the Morrisville Municipal Authority (MMA) WRRF. A biochar producing facility is being designed for the Edmonds WWTP modeled after the successful resource recovery and renewable energy production process at MMA. MMA has transitioned from disposing of Class B biosolids to recovering resources including dried Class A biosolids, activated biochar, and concentrated nutrients. SVCW has transitioned from sludge incineration to anaerobic digestion, biosolids drying, and pyrolysis to produce biochar. Edmonds solids processing will transition from disposing of ash from sludge incineration to having the flexibility to recover dried Class A biosolids, activated biochar, and concentrated nutrients. Edmonds will be prepared for changing biosolids regulations and markets.

SpeakerParry, David

Presentation time

14:10:00

14:30:00

Session time

13:30:00

14:30:00

SessionEvolution of Marketing, Technology, and Regulations for Biosolids Beneficial Uses

Session number212

TopicBiosolids and Residuals, Fundamental Level, Policy and Regulation, Public Communication and Outreach

Author(s)

D. ParryP. RandolphG. MockosA. Akela

Author(s)D. Parry1; P. Randolph2; G. Mockos3; A. Akela4;

Author affiliation(s)Jacobs, UT1; City of Edmonds, WA2; BHC Consultants, WA3; Silicon Valley Clean Water, CA4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2020

DOI10.2175/193864718825157790

Volume / Issue

Content sourceWEFTEC

Word count4

Enhancing Anaerobic Digestion Performance With The Microbial Hydrolysis Process

Abstract

Introduction:
Anaerobic digestion is a proven technology to stabilize solids from water resource recovery facilities and produce biogas. The objective of this research is to enhance anaerobic digestion performance by increasing the volatile solids reduction (VSR) and biogas production, and consequently reducing the amount of biosolids produced. Typically, a well-performing anaerobic digester can achieve 55 percent VSR when fed a combination of primary and secondary sludge from a water resource recovery facility (WRRF). High-performing digestion systems can achieve 60 percent VSR or higher, but none (until now) have achieved over 70 percent VSR. With professors at Brigham Young University (Hansen, Jaron C., et al., Biofuel Research Journal Vol. 8 Issue 3 2021), Jacobs developed the Micro Hydrolysis Process (MHP) using Caldicellulosiruptor bescii (C. bescii), a hyper-thermophilic bacterium that enhances the performance of any anaerobic digestion process. The MHP flow diagram is shown in Figure 1. The C. bescii bacteria and associated enzymes hydrolyze cellulose and other recalcitrant volatile solids that are otherwise resistant to digestion into volatile acids. These hydrolyzed volatile solids are fed to an anaerobic digester where methanogens convert them into biogas. One configuration of MHP feeds digestate from an anaerobic digester to a hydrolysis tank populated with C. bescii for a hydraulic retention time of at least 2 days at 75 degrees C. The hydrolyzed digestate is then returned to the digester to complete the digestion process by converting volatile acids into methane and carbon dioxide. MHP is compatible with any anaerobic digestion process including mesophilic anaerobic digestion (MAD), thermophilic anaerobic digestion (TAD), and thermal hydrolysis process (THP). The increase in VSR results in corresponding increases in biogas production and reductions in residual biosolids. The value of the additional biogas and cost savings of producing less biosolids reduce the operating costs of a WRRF.
Methodology: The performance of anaerobic digestion with MHP was tested at lab-scale and pilot-scale systems on solids from three different WRRFs: City of Gresham Wastewater Treatment Plant in Gresham, OR with MAD and fats, oils, and grease (FOG) addition; Encina Water Pollution Control Facility (WPCF) in Carlsbad, CA with MAD; and Oakland County's Clinton River WRRF in Pontiac, MI with THP and MAD. The lab-scale system consisted of a test and control system: each with a 10 Liter (L) digester and a 5L hydrolysis tank. Figure 2 is a picture of the lab-scale system and Figure 3 is a simple process flow diagram of the system. The pilot-scale system consisted of a test system with a 1,200L digester and a 500L hydrolysis tank and a control system with a 1,200L digester. Figure 4 is a picture of the pilot-scale system and Figure 5 is a simple process flow diagram of the system. All tanks were mixed, heated, and automatically fed from digester feed tanks.
The test and control systems were operated to simulate the full-scale digester operation for feed, retention time, and transfer rate between the digester and hydrolysis tank. Characteristics of the feed and contents of the digesters and hydrolysis tanks were measured using standard methods. The stability of the digestion process was monitored measuring Volatile Fatty Acids, Alkalinity, and Ammonia. The VSR of the digesters was the key indicator of performance and was determined from the TS and VS fed to the digesters compared to the TS and VS withdrawn from the digesters.
Lab-scale tests for Gresham and Encina were conducted in the Gresham lab. Pilot-scale tests for Oakland County were conducted in the Clinton River WRRF lab. Labs at each WRRF were used to measure the characteristics of the feed and performance of the full-scale digesters.
Findings:
The digestion performance of the three WRRFs are indicated by the VSR. Results from lab-scale, and pilot-scale digestion systems have demonstrated significant increases in VSR compared to already high-performing digestion systems (e.g., THP and MAD). VSRs were observed to increase from 60 percent without MHP to greater than 75 percent with the addition of MHP. Figures 6-8 show the VSR results of the test and control systems compare to the full-scale systems. In all cases the MHP increased the VSR from current operation of 58-60 percent to over 75 percent VSR. Results were used to calibrate a process model (Sumo) to predict digestion performance for full scale facilities with different feed characteristics. Based on the results, conceptual designs were prepared for implementation at three WRRFs with three different technologies: MAD, TAD, and THP and MAD. The details of these designs are being reviewed by each utility and can be presented in the full paper.
Significance:
The significance of the research and development of MHP is the discovery of a new technology that enhances the performance of anaerobic digestion to the highest level achievable to date. Anaerobic digestion performance increased with the addition of MHP in tests on three different WRRFs. MHP increased the VSR from 58-60 percent to over 75 percent. The increase in VSR corresponded to a 25% increase in biogas production and a 25% decrease in biosolids production. Conceptual designs for implanting MHP have been developed for a MAD, TAD, and THP digestion system.

Anaerobic digestion (AD) performance was enhanced with the microbial hydrolysis process (MHP) using Caldicellulosiruptor bescii (C. bescii), a hyper-thermophilic bacterium. The volatile solids reduction (VSR) was tested from AD of solids from three water resource recovery facilities (WRRF). The addition of MHP enhanced the performance of all three AD systems from a VSR of 60 percent to over 75 percent. This increase in VSR corresponds to an increase in biogas and decrease in biosolids.

SpeakerParry, David

Presentation time

13:35:00

13:50:00

Session time

13:30:00

15:00:00

TopicIntermediate Level, Biosolids and Residuals, Energy Production, Conservation, and Management, Research and Innovation

Author(s)

Parry, David

Author(s)Dave Parry1; Maddy Fairley-Wax2; Corey Klibert3; Scott McClelland4; Alan Johnston5; Mike Daniels6

Author affiliation(s)Jacobs, Salt Lake City, UT1; Jacobs, Ann Arbor, MI2; Jacobs, Portland, OR3; Encina Wastewater Authority, Carlsbad, CA4; City of Gresham, Gresham, OR5; Oakland County WRC, Pontiac, MI6

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158604

Volume / Issue

Content sourceWEFTEC

Word count10

Enhancing Anaerobic Digestion Performance with the Microbial Hydrolysis Process

Abstract

Introduction: Anaerobic digestion is a proven technology to stabilize solids from water resource recovery facilities (WRRFs) and produce biogas. Enhancing anaerobic digestion would increase the volatile solids reduction (VSR), biogas production, and reduce the residual biosolids. The objective of this research was to explore how much the VSR could be increased in digestion with the addition of new technology: Microbial Hydrolysis Process (MHP). Typically, a well-performing anaerobic digester can achieve 55 percent VSR when fed a combination of primary and secondary sludge from a WRRF. High-performing digestion systems can achieve 60 percent VSR or higher, but none (until now) have achieved over 70 percent VSR. Jacobs with professors at Brigham Young University (Hansen, Jaron C., et al., Biofuel Research Journal Vol. 8 Issue 3 2021), developed the Microbial Hydrolysis Process using Caldicellulosiruptor bescii (C. bescii), a hyper-thermophilic bacterium that enhances the performance of any anaerobic digestion process. The MHP digestion process flow diagram is shown in Figure 1. The C. bescii bacterium and associated enzymes hydrolyze cellulose and other recalcitrant volatile solids that are otherwise resistant to digestion into volatile acids. These hydrolyzed volatile solids are fed to an anaerobic digester where methanogens convert them into biogas. One configuration of MHP feeds digestate from an anaerobic digester to a hydrolysis tank populated with C. bescii for a hydraulic retention time of at least 2 days at 75 degrees C. The hydrolyzed digestate is then returned to the digester to complete the digestion process by converting volatile acids into methane and carbon dioxide. MHP is compatible with any anaerobic digestion process including mesophilic anaerobic digestion (MAD), thermophilic anaerobic digestion (TAD), and thermal hydrolysis process (THP). The increase in VSR results in corresponding increases in biogas production and reductions in residual biosolids. The value of the additional biogas and cost savings of producing less biosolids reduce the operating costs of a WRRF. Methodology: The performance of anaerobic digestion with MHP was tested at lab-scale and pilot-scale systems on solids from three different WRRFs: City of Gresham Wastewater Treatment Plant in Gresham, OR with MAD and fats, oils, and grease (FOG) addition; Encina Water Pollution Control Facility (WPCF) in Carlsbad, CA with MAD; and Oakland County's Clinton River WRRF in Pontiac, MI with THP and MAD. The lab-scale system consisted of a test and control system: each with a 10 Liter (L) digester and a 5L hydrolysis tank. Figure 2 is a picture of the MHP digestion lab-scale system and Figure 3 is a process flow diagram of the system. The pilot-scale system consisted of a test system with a 1,200L digester and a 500L hydrolysis tank and a control system with a 1,200L digester. Figure 4 is a picture of the pilot-scale MHP digestion system and Figure 5 is a process flow diagram of the system. All tanks were mixed, heated, and automatically fed from digester feed tanks. The test and control systems were operated to simulate the full-scale digester operation for feed, retention time, and transfer rate between the digester and hydrolysis tank. Characteristics of the feed and contents of the digesters and hydrolysis tanks were measured using standard methods. The stability of the digestion process was monitored measuring Volatile Fatty Acids, Alkalinity, and Ammonia. The VSR of the digesters was the key indicator of performance and was determined from the TS and VS fed to the digesters compared to the TS and VS withdrawn from the digesters. Lab-scale tests for Gresham and Encina were conducted in the Gresham lab. Pilot-scale tests for Oakland County were conducted in the Clinton River WRRF lab. Labs at each WRRF were used to measure the characteristics of the feed and performance of the full-scale digesters. Findings: The digestion performance of the three WRRFs are indicated by the VSR. Results from lab-scale, and pilot-scale digestion systems have demonstrated significant increases in VSR compared to already high-performing digestion systems (e.g., THP and MAD). VSRs were observed to increase from 60 percent without MHP to greater than 75 percent with the addition of MHP. Figures 6-8 show the VSR results of the test and control systems compare to the full-scale systems. In all cases the MHP increased the VSR from current operation of 58-60 percent to over 75 percent VSR. Results were used to calibrate a process model (Sumo) to predict digestion performance for full scale facilities with different feed characteristics. Based on the results, conceptual designs were prepared for implementation at three WRRFs with three different technologies: MAD, TAD, and THP and MAD. The details of these designs are being reviewed by each utility and can be presented in the full paper. Significance: The significance of the research and development of MHP is the discovery of a new technology that enhances the performance of anaerobic digestion to the highest level achievable to date. Anaerobic digestion performance increased with the addition of MHP in tests on three different WRRFs. MHP increased the VSR from 60 percent to over 75 percent. The increase in VSR corresponded to a 25% increase in biogas production and a 25% decrease in biosolids production.

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

SpeakerParry, David

Presentation time

10:45:00

11:15:00

Session time

8:30:00

11:45:00

SessionSession 12: Innovative Processes in Anaerobic Digestion

Session number12

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicResearch & Innovations

Author(s)

D. Parry

Author(s)D. Parry1, M. Fairley-Wax2, C. Klibert3, S. McClelland4,

Author affiliation(s)Jacobs1; Jacobs2; Jacobs3; Encina Wastewater Authority4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158813

Volume / Issue

Content sourceResiduals and Biosolids

Word count10

Importance of Digester Foaming Control in Moving Towards Energy Neutrality

Abstract

INTRODUCTION Sustainability is increasingly more important for the operation of wastewater treatment plants. To meet sustainability goals and better energy recovery, the current business as usual approach to anerobic digester operation is not ideal. Improving digester operation is crucial for effective energy recovery. Having a reactive approach to digester foaming prevents optimal digester performance and causes other problems like digester failure, poor biogas recovery, uncontrolled release of contaminated waste to the environment and odour. Figure 1 shows some of these impacts. The best way to mitigate digester foaming is through robust design, but if this is not possible there are several operating conditions that can be improved to control foaming. Sydney Water Corporation (SWC) recognised the importance of preventing anaerobic digester foaming. Digester foaming at SWC plants has been caused by multiple different issues and foam management can therefore be largely reactive. There are operational methods and digester design features in place at some plants that aim to reduce the occurrence of the impacts of foam events, however this is not widespread or consistent. Investigation into 5 plants was undertaken to determine the likely causes of digester foaming and gas entrainment and the most effective ways to manage this and where possible through design changes as upgrades occur. For plants where design changes are not possible in the near future, key operating conditions were reviewed, early warning signs for digester foaming events determined and management practices recommended to mitigate digester foaming. METHODOLOGY Digester foaming was investigated at 5 SWC Water Resource Recovery Plants (WRRP), including Cronulla, Malabar, Warriewood, West Hornsby and Hornsby Heights. Digester operation data was analysed to determine the likely causes of digester foaming issues and recommendations on proactive and reactive measures for foam management including how to prevent or mitigate foaming at these plants and across broader SWC plants were established and operator training provided. Digester operation parameters and recommended monitoring were also outlined. Best practice digester design to minimise foaming and maximise energy production was investigated, drawing on international experience. These design components were presented to SWC designers, along with recommended implementation methodologies. RESULTS The main issues causing digester foaming at the SWC plants investigated were seasonal foaming related to activated sludge processes, lack of effective redundancy or contingency measures associated with the digester process, and illegal industrial discharges to the incoming sewer. There are other fundamental operating issues that cause digester foaming, such as running with one digester offline for extended periods (for example, at 2 plants digesters were offline due to issues with digester lids, which resulted in excessive volatile solids load in remaining digester/s particularly when food waste was accepted), turning off mixing, high volatile solids loading rates in digesters, poor temperature control, unstable feed to the digesters, and large step changes in temperature and feed. Figure 2 shows the volatile solids (VS) loading rate and specific volatile solids loading rate (SVSLR) in the primary digester at one of the plants where primary and secondary digesters are currently operated in series. At this plant, there is inadequate solids retention time (SRT) in the digesters, as well as a high VS loading to the primary digester. The average VS load to the primary digester was 3.74 kgVS/m3.d and a peak loading rate of 4.5 kgVS/m3.d, where the recommended range is 1.6-3.2 kgVS/m3.d . Therefore, the anaerobic digesters are operated beyond the typical recommended VS loading rates. The high VS loading rate is also exacerbated by the unloading/loading sequence of flow, which results in intermittent VS loading, rather than constant loading across the day. The high VS load impacts the stability of the sludge and increases risk of foaming in the digesters. The SVSLR is a variation of VS loading rate that considers the VS in the digester as a function of active biomass. However, SVSLT may not account for the feedstock other than the wastewater sludge such as high strength organic matter. The maximum recommended SVSLR for mesophilic digestion without any pre-treatment is 0.16 kg VS/kg VS in digester day. As shown in Figure 1, along with the VS loading rate, the SVSLR for the primary digester is consistently above the recommended limit, making it vulnerable to the digester foaming and failure with fluctuation in digester loading rate. Best practice digester design to avoid foaming issues and maximise energy recovery include the use of standpipes for surface overflow (see Figure 2) and emergency withdrawal via p-traps (see Figure 3), minimisation of the top water surface area, installation of fixed covers and external gas storage, the use of pumped mixing to reduce short-circuiting and having adequate redundancy to ensure that there is no single point of failure. Digesters should have a conical shape to facilitate grit removal and more efficient mixing. Wasting foam from the surface in secondary activated sludge processes will also minimise the amount of trapped foam, improving conditions in the downstream digesters. Rolling out design changes in a systematic way as digesters are taken offline for planned maintenance is an effective way to facilitate continuous removal of foaming issues from upgraded digesters. In addition to benefits of maximising energy generation, achieving maximum hydraulic capacity within existing digesters by having external gas holders and running digesters full may allow capital upgrades of digesters to be delayed for a number of years if not decades, further improving sustainability of WRRPs. Where design changes cannot be implemented, there are operational improvements that can be made to manage digester foaming and increase energy production. Generally, if there are filamentous bacteria in the activated sludge bioreactor at a plant, there is a high likelihood of foaming in the digester. These foaming incidents are manageable through adjusting the operating parameters in the activated sludge plant. Digesters should be brought online slowly with small step increases in feed and temperature over time. A common misconception is that digester mixing should be turned off to control a foam event, however mixing should be turned down. Digesters should be operated with a top water level high into the lid, with sprays used to suppress foam and move foam to wasting points. Digested sludge should be withdrawn from the top and bottom of the digester, and consideration given to alkalinity correction when the pH in the digester starts to drop. Running the digesters without any safety factor and running some process equipment at loading rates higher than designed for will increase the risk of process upsets that could also contribute to foaming. Allowing a safety factor in terms of solids retention time and volatile solids loading provides plants with the ability to cope with under upset conditions and avoids the need to detune the digesters and the plant to minimise the risk of foaming. CONCLUSION By successfully managing digester foaming and operating digesters in a manner than maximises power generation, WRRPs can achieve more effective energy recovery and meeting energy sustainability and neutrality goals. Some fundamental issues that generally arose to cause digester foaming were: -Running with one digester offline for long periods resulting in much higher loadings and shorter SRT than originally designed -High VS loading rates in the digesters -Reduced effective SRT due to mixing being turned off and accumulation of grit and screening -Mixing generally not designed for current solids loading due to intensification -Poor temperature control for the digesters -Unstable feed to the digesters -Large step changes in temperature or feed due to heater failure or storm conditions Foaming subsequently resulted in lower biogas production, high costs for digester reinstatement, and poor run times on biogas engines due to poor biogas quality. Robust digester design which minimises digester foaming and gas entrainment is the most preferable management mechanism, and changes to digester components can be implemented over time as maintenance is undertaken. Where design changes are not possible, operational improvements can be made to greatly reduce digester foaming. This paper outlines some best practice measures that can save millions of dollars by avoiding catastrophic foaming events and will help maximise biogas production and energy generation.

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

SpeakerParry, David

Presentation time

11:15:00

11:45:00

Session time

10:45:00

11:45:00

SessionSession 03: Digestion Optimization and Troubleshooting

Session number03

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicDigestion & Stabilization

Author(s)

D. Parry

Author(s)A. McDonald1, J. Cesca2, G. Bharambe3, D. Parry4, J. Gonzalez5,

Author affiliation(s)Jacobs1; Sydney Water Corporation2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158821

Volume / Issue

Content sourceResiduals and Biosolids

Word count11

Description: Lessons Learned from an Anaerobic Digestion Improvements Project at the Jackson Pike...

Lessons Learned from an Anaerobic Digestion Improvements Project at the Jackson Pike WWTP in Columbus, Ohio

Abstract

Introduction: This project involved planning the upgrades to the digester improvements at the Jackson Pike Wastewater Treatment Plant (JPWWTP) in Columbus, Ohio. Figure 1 is an aerial of the JPWWTP. This paper provides insights and lessons learned where Jacobs served as the consulting engineer working with the JPWWTP managers, engineers, operators, and maintenance staff (City). The JPWWTP has a design capacity of 68 MGD with a peak wet weather secondary treatment capacity of 150 MGD. There are six 1.0 MG digesters with membrane covers and a pumped mixing system. The design average sludge flow to the digesters is 249,000 gpd at 5.3 percent solids with a volatile solids loading of 87,000 lbVS/day. Figure 2 is a solids process flow diagram with flows and loads for average conditions. Six 1.0 MG mesophilic anaerobic digesters provide solids stabilization and produce digester gas. A digester gas-fueled cogeneration system has been designed with construction set to begin in 2021. The cogeneration system is projected to provide about half of the total electricity used at the plant. Biosolids from the plant are made into a popular organic mulch and soil enrichment product (Com-Til) at the Compost Facility operated by the Division of Sewerage and Drainage. The key driver for this project is the current digester system nearing the end of its life and is ready for an upgrade. For example, the existing membrane digester covers have a relatively short life of six to 8 years and two are currently in need of replacement. Figure 3 is a picture of an existing digester cover. An aged, custom 'trombone valve' mixing system circulates 1,000 gpm with a 20 hp pump providing only 1.4 turnovers per day. Figure 4 is a picture of the trombone valve mixing equipment. With the inadequate mixing, grit accumulates at the bottom of the digesters requiring frequent cleaning every six years when the covers are replaced. Digester improvements are needed for the digester covers, mixing, and heating systems. Planning: The entire solids processing system was evaluated during the planning period. The flows and solids loadings to the digesters were determined from historical data of primary and secondary sludge production and thickening. Future flows and loads due to growth will be routed to the sister plant (Southerly). Existing primary and secondary sludge holding tanks provide flexibility in feeding the digesters. Sludge is pumped through grinders before entering the digesters. Digested biosolids are pumped to storage tanks before dewatering. Class B Biosolids are trucked to the Compost Facility where a soil enrichment product is made for beneficial use. Since Class B biosolids are beneficially used, producing Class A Biosolids through anaerobic digestion is not required. High performance anaerobic digestion processes were evaluated including mesophilic, acid-gas, various configurations of thermophilic, and thermal hydrolysis. Considerations of alternate digestion processes included: - Digester gas production and quality - Digester capacity - Ability to accept co-digestion feedstocks - Dewatering performance Planning was conducted through a series of collaborative workshops for the digestion improvements. The focus of the improvements was on the digester covers, digester mixing, and digester gas storage. The overall objectives were clarified at the beginning of the planning period. A cost benefit comparison was conducted using multi-criteria analysis. Non-economic objectives were compared to the economic objective of lower life cycle cost. Non-economic criteria included operation & maintenance, process reliability, regulatory, sustainability, and community considerations. Specific objectives were identified and prioritized for each component as follows: Digester Covers - O&M: life expectancy, odor containment - Process Reliability: compatibility with digestion processes (e.g., thermophilic) - Sustainability: digester gas containment, digester gas storage Digester Mixing - O&M: grit entrainment, maintenance accessibility, sensitivity to liquid level, energy use - Process Reliability: scum/foam management, ragging, redundancy, mixing effectiveness - Sustainability: digester gas production Preliminary Design: A preliminary design was completed for each of the different options for digester covers, digester mixing, and digester gas storage. The options were ranked based on non-economic criteria. Life cycle costs were determined based on capital cost and operating cost estimates. The options were then compared taking life cycle cost and non-economic benefits into account. The following options were considered: Digester Covers: - Floating - Gas Floating - Carbon Steel Fixed - Stainless Steel Fixed - Concrete Fixed Digester Mixing: - Existing trombone valve pumped - Pumped jet and nozzle - Draft tube - Linear motion mixers The digester covers, mixing, and gas storage options were considered as part of an overall evaluation. Continuing with mesophilic digestion was selected with the ability to convert to thermophilic digestion in the future if additional capacity were required. Sludge withdrawal from the digesters for removal of foam and floatables from the surface were considered along with removal of grit from the bottom. Attention was given to the gas dome for the distance between the digester gas piping and the maximum sludge level to avoid foam in the gas piping. Biogas use and heat supply were covered by a separate cogeneration project. Replacement of the water to sludge heat exchangers was addressed. Project Results: The results of the cost benefit comparison of the digester covers and mixing are summarized in Tables 1 and 2. The digestion improvements solution with the most benefits for the life cycle cost is concrete covers with linear motion mixers. A combination of four concrete covers and two membrane covers was ranked second. Stainless steel covers ranked third. For mixing, linear motion mixers ranked first and the existing mixing system ranked second. However, the existing system would require new pumps and nozzles for adequate mixing. The pumped nozzle hydraulic mixing system would provide adequate mixing but would have a higher energy demand. Gas storage would be provided by gas membrane holders at ground level or on top of the concrete covers. The results of the multi-criteria analysis enabled the City to consider the pros and cons of the different options and make an informed decision on the digestion improvements. Lessons learned from this digestion improvement project will provide guidance to managers, engineers, operators, and maintenance staff of other water resource recovery facilities that are planning on upgrading their anaerobic digestion facilities.

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

SpeakerParry, David

Presentation time

8:30:00

9:00:00

Session time

8:30:00

11:15:00

Session number19

Session locationGreater Columbus Convention Center, Columbus, Ohio

TopicAnaerobic Digestion, Biogas, Biosolids

Author(s)

D. Parry

Author(s)D. Parry1; M. Hatzigeorgiou2

Author affiliation(s)Jacobs; 1Jacobs; 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May, 2022

DOI10.2175/193864718825158383

Volume / Issue

Content sourceResiduals and Biosolids

Word count17

Lessons Learned From The San Jose Cogeneration Facility Project

Abstract

Introduction:
Biogas-fueled cogeneration systems play a key role at water resource recovery facilities (WRRFs) recovering energy and moving towards heat and power self-sufficiency. Managers of WRRFs that are considering installing, expanding, or upgrading a biogas-fueled cogeneration system will benefit from lessons learned from the Cogeneration Facility Project at the San Jose-Santa Clara Regional Wastewater Facility in San Jose, California. The City of San JosÃ© (City) Santa Clara Regional Wastewater Facility (RWF) provides secondary and advanced tertiary wastewater treatment for the cities of San JosÃ© and Santa Clara and multiple tributaries. The RWF has a rated capacity of 167 MGD and processes wastewater solids using anaerobic digestion. The RWF has used cogeneration engines for over 30 years to provide heat and power for the facility. However, the existing cogeneration system reached the end of its useful life. The City decided to replace the existing cogeneration engines with an updated system to continue providing the RWF's heat and power demands. The San Jose Cogeneration Facility was designed and constructed through a progressive design-build process. The design was centered around four 3.5 MW engine-driven generator units. The Cogeneration Facility is shown in Figure 1 and the engine room in Figure 2. Table 1 is a project fact sheet with key specifications. The 14 MW system has the capacity to meet the projected RWF electrical demand of 13 MW in 2040. Space for a fifth 3.5 MW unit is provided to have a firm capacity of 14 MW in the future with one unit out of service. Experience throughout the planning, design, construction, and commissioning of the project is shared. Insights discussed: - Early selection of cogeneration units - Integration of cogeneration with standby power systems - Biogas treatment and management - Fuel blending of biogas with natural gas and landfill gas - Emission requirements met with post-combustion treatment - Heat recovery and management - Business-case decision making throughout the project - Startup considerations
Findings: The project included early selection of the cogeneration and gas treatment systems in the initial design stage. By selecting the equipment early in the design, subsequent design stages were tailored to known specifications. The cogeneration units were selected through an evaluated bid process that quantified the value of electrical efficiency, fuel blending capability, gas compression requirements, cost of parts, and maintenance requirements. The cogeneration facility is integrated with two separate utility power feeds and standby generators. This integrated power system provides a reliable power supply for the RWF. Protective relays were included to meet the electric utility interconnection agreement and allow for excess power to be supplied to the utility grid. The design provides for supplemental natural gas and using landfill gas in the future. Because of the significant amount of natural gas required (as much as 50 percent of the fuel supply) to meet the plant power demand, these cogeneration units need to meet the emission requirements of a natural gas fueled cogeneration system. Digester gas treatment protects both the engines and the engine exhaust gas treatment equipment. The biogas treatment system is shown in Figure 3. Biogas treatment includes hydrogen sulfide removal via iron sponge, moisture reduction, siloxane removal via activated carbon, and particulate removal. In this case, gas treatment followed gas compression and moisture removal. Consequently, the gas treatment occurs at a relatively high pressure of 50 psig. Each engine is equipped with a dedicated gas blending system to allow operation using any blend of biogas (digester gas and landfill gas) and natural gas. The gas blending system responds to changes in digester gas production to achieve a power output setpoint without requiring a system shutdown. Engine timing and air/fuel ratio are automatically controlled based on the blend of digester gas and natural gas. Peak power output of a cogeneration unit varies with the amount of natural gas in the fuel blend. Exhaust gas treatment was provided to meet Bay Area Air Quality emission limits. Exhaust gas treatment consisted of selective catalytic reduction (SCR) for nitrogen oxide (NOx) reduction and an oxidative catalysis for carbon monoxide (CO) and volatile organic carbon (VOC) reduction. Extensive exhaust gas treatment was required because of the significant amount of supplemental natural gas used (greater than 10 percent of the fuel supply). Heat generated by the cogeneration units is recovered from the engine and exhaust gas to provide building and process heating demands. New auxiliary boilers provide supplemental and backup heating for the RWF. Rejection of low temperature heat that can't be beneficially used is provided by cooling towers. The anaerobic digestion system at the RWF is being converted from mesophilic anaerobic digestion to a temperature-phased anaerobic digestion (TPAD) system. The heat supply system was designed to accommodate the higher temperatures and heat requirements for the TPAD system. The heat recovery and hydronic heat supply system was coordinated with the TPAD project team to meet the heating demands both in terms of temperature and amount of heat while maximizing heat recovery from the engines. Using the progressive design-build delivery method enabled collaboration between the Owner and the Design-Builder, particularly during the early design stages. Approximately halfway through preliminary design, it became clear that the project required value engineering to reduce costs within the City's budget. Approximately 20 percent of the project cost was reduced because of a value engineering effort with the City and the Design-Builder. Business case evaluations were conducted throughout the project for decision-making based on meeting multiple objectives of economic, environmental, social, and operational categories. Life cycle cost to benefit ratios were compared for different options to guide selecting the best option. There were several startup procedures that could be followed on other projects. The biogas treatment system was tested and treated gas was used in the boilers prior to sending it to the engines. The engines were started on natural gas first to test ancillaries prior to running on biogas.
Significance: The significance of this project come from several lessons learned including:
Early selection of cogeneration units and gas treatment system enables an efficient design process
Integrating the utility power feeds with the cogeneration units and standby generators results in a reliable plant power supply
Additional exhaust gas treatment (such as oxidation catalysts and selective catalytic reduction) can be used with comprehensive biogas treatment to meet strict air quality management districts.
A fuel blending system for biogas and natural gas, provides operating flexibility
Heat recovery from the engines can be designed to be compatible with a higher temperature thermophilic digestion process.
Costs can be controlled during design with a progressive design build procurement and value engineering.

The new Cogeneration Facility at the City of San Jose and Santa Clara Regional Wastewater Facility was designed and constructed through a progressive design-build process and includes four 3.5 MW internal-combustion, engine-driven generator units for a total capacity of 14 MW. Lessons learned throughout the planning, design, construction, and commissioning of the project is shared.

SpeakerParry, David

Presentation time

09:25:00

09:40:00

Session time

08:30:00

10:00:00

TopicIntermediate Level, Utility Management and Leadership

Author(s)

Parry, David

Author(s)Dave L. Parry1; Nathan Ebbs2; ohn Ryan3

Author affiliation(s)Jacobs, Salt Lake City, UT1; Jacobs, Corvallis, OR2; Jacobs, San Jose, CA3