Barber, William, Barber

Bill Barber is a professional engineer with PhD and degree in Chemical Engineering. Bill has worked in consulting for multi-national companies,...

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About Barber, William

Bill Barber is a professional engineer with PhD and degree in Chemical Engineering. Bill has worked in consulting for multi-national companies, technical development and sales, and for the UKs largest Water Company, United Utilities. He has worked on projects in the UK, Europe, Asia, Australia, New Zealand and North America. Bill has written the IWA textbook on thermal hydrolysis as well as numerous peer-reviewed articles. He is a reviewer for several academic journals related to wastewater and sludge management.

Barber, William

Titles from this speaker

Description: Combining thermal hydrolysis with advanced thermal conversion processes for...

Combining thermal hydrolysis with advanced thermal conversion processes for micro-contaminant destruction

Abstract

Abstract: There is growing concern related to the potential health impacts of continued application of biosolids, produced during wastewater treatment, to land. These relate to a variety of micro-contaminants such as perfluorinated compounds (PFAS etc), microplastics and other xenobiotic compounds. This has led to a trend in the use of advanced thermal processes such as pyrolysis and gasification, and renewed interest in incineration in a bid to diverge away from land application. However, these processes are energy intensive as they require drying upstream. This paper looks at how thermal hydrolysis, both with and without digestion can make these processes sustainable by reducing energy demands due to fundamental improvements in dewaterability and presents results from research where the technologies have been combined to optimize destruction of micro-contaminants. KEYWORDS Thermal hydrolysis; pyrolysis; micro-contaminants; energy demand; drying INTRODUCTION Thermal hydrolysis (TH), a popular pre-treatment to digestion with approximately 130 facilities worldwide including several in North America, has typically been associated with producing a high-quality biosolids product for land application. In combination with improved digestion performance, elevated dewatering (typically over 30% dry solids) results in less than half the biosolids cake compared to standard digestion. However, less well known is that thermal hydrolysis was initially conceived as a dewatering aid prior to thermal processing. Although thermally-hydrolysed digested cake dewaters well compared to other process trains, previous work has shown that having digestion downstream of thermal hydrolysis actually deteriorates the dewaterability potential of the hydrolysed cake. This can be by as much as 20% points. This has been shown to be due to the reproduction of extracellular polymers as a consequence of biological metabolism. The dewaterability improvements afforded by thermal hydrolysis become of interest with advanced thermal processing. Systems such as pyrolysis and gasification are limited as they are fundamentally dependent on requiring a dried feedstock, typically over 85% solids. Drying of sludge is extremely energy (and subsequently carbon) intensive. Driers usually require 900 -- 1,100 kWhr energy per metric tonne water evaporated. Even with extreme energy recovery this is still orders of magnitude higher than the energy needs of aeration which are considered high and account for half of the energy needs of wastewater treatment. The aim of this work is to highlight the influence thermal hydrolysis has on downstream energy requirements of thermal processing systems with respect to reducing the large energy demands of drying prior to thermal destruction. The work will show the impact of hydrolysis both with and also without digestion on these thermal systems and will look at research work into the impacts of hydrolysis on outputs of pyrolysis. This work is based on a variety of aspects. A study was set up to determine the influence of thermal hydrolysis and operating conditions, with and without digestion on dewaterability and ultimately on drying and advanced thermal processing. The study was a combination of theoretical determinations based on site-data, data collection from multiple sites and analysis, investigation of full-scale operating plants which combined thermal hydrolysis with thermal processing, and a review of literature on combining thermal hydrolysis with advanced thermal processing looking at the impacts of thermal hydrolysis on pyrolysis. As an example of a full-scale facility, thermal hydrolysis was installed on half of the produced waste activated sludge at Psyttalia in Athens, Greece as part of a project to become more energy efficient. Prior to thermal hydrolysis installation, sludge was digested and dried in 4 drum driers to 93% dry solids. Biogas produced from the site was diverted to the drying plant to meet its energy demand. Following a combination of dewatering optimization with thermal hydrolysis, dewatering improved from 21% to 31% dry solids. The influence of this on the energy demands of the drying plant is shown in Figure 1. Prior to the improvements, almost 75% of the biogas was consumed by drying, and the energy demand reduced by 40%. In combination with more biogas generated via digestion, almost three times additional energy was available for non-drying purposes such as the generation of renewable energy. In this instance the energy required for steam to run thermal hydrolysis, was available via high-grade heat recovered from co-generation. Figure 2 expands that data to look at different hydrolysis configurations combined with hydrolysis without digestion. It is based on the potential impacts on dewaterability as shown in Figure 3. Surplus energy is shown as the energy left after accommodating the energy needs of both drying and thermal hydrolysis. In this instance, thermal hydrolysis placed after digestion -- to redestroy the extracellular polymers, provides the greatest overall energy benefit. In this example, thermal hydrolysis without digestion is assumed to have no biogas benefit. However, other data, at both full- and lab-scale show separate digestion of the liquid fraction of the dewatered cake. Here, cake is at 50% dry solids or above, and biogas is produced from the liquid. Laboratory work has looked specifically at energy recovery from waste activated sludge (WAS) with/without thermal hydrolysis and compared this with energy recovered from separate liquid and solid fractions immediately following thermal hydrolysis combined with dewatering (i.e. with no downstream digestion of the sludge). The results showed approximately 30% increase in methane production from 11 litres to 15 litres produced/litre WAS processed with standard thermal hydrolysis followed by digestion. However, when the WAS was directly dewatered and the liquid and solid fractions were separated, almost as much biogas was produced from the liquid fraction with a further 40% from the solids. In combination this resulted in over 60% more energy recovered compared to absence of thermal hydrolysis. The work then studied at the solid dewatered fraction with respect to combining it with drying and downstream pyrolysis. This work investigated the influence of various operating parameters on the production of char and its energy content. Whilst thermal hydrolysis has been associated with the production of a high-quality biosolids agricultural product, its influence on sludge reduction, and more importantly dewaterability, make it complementary to thermal processes. Better dewatering fundamentally reduces energy needs of drying, and is dependent on the configuration of thermal hydrolysis. Combining thermal hydrolysis, either with or without digestion, with thermal processing can help with the large energy requirements of advanced thermal processing facilities.

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

SpeakerBarber, William

Presentation time

11:30:00

11:45:00

Session time

10:45:00

12:15:00

SessionIntensification of Anaerobic Digestion

Session numberITT Session 14

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAnaerobic co-digestion, Biomethane, Lipids/proteins/carbohydrates ratio, TWAS, Manure, SSO, Anaerobic Digestion, Biochar, Biosolids, Circular Economy, Microbial communities, PFAS/Emerging Contaminants, Thermal drying, THP, THP, CAMBI

Author(s)

Barber, William

Author(s)W. Barber1

Author affiliation(s)Cambi Inc, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159775

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count12

Determining the Carbon Footprint of Biogas Production from Sewage Sludge

Abstract

Abstract: Anaerobic digestion of sewage has been practiced over 150 years and results in the production of a methane enriched biogas which is considered a renewable energy source. After processing, biogas can be used directly to produce electricity via a co-generation plant, or following removal of the carbon dioxide within it, be used as a substitute to natural gas, or after compression, vehicle fuel. By displacing fossil-fuels, use of this biogas can help Water Utilities with their quest to become carbon-neutral. However, to make biogas, sludge needs to be anaerobically digested, the biogas cleaned, and the nutrients released to the digestate need to be destroyed. Furthermore, there are direct methane emissions from storage, leaks and incomplete processing. This paper looks to quantify these to determine the carbon impact of using biogas produced from municipal digestion of sewage sludge. KEYWORDS Anaerobic digestion; biogas; biomethane; carbon footprint INTRODUCTION There is increasing concern over the impacts of anthropogenic activities on the climate. This is leading to growing interest in renewable energy as an alternative to fossil-fuels. Biogas, a by-product generated from sewage treatment, is a valuable source of renewable energy. It can be used to generate electricity from engines which displaces energy made elsewhere at a power station resulting in a reduction in carbon footprint. However, to make biogas, sludge has to be anaerobically digested, and both the gas and liquid streams need to be processed (summarized in Figure 1). This processing generates a carbon impact in the form of electricity consumption (for example to mix digesters and to run conveying systems), chemical use (polymers for dewatering and carbon for nutrient removal) and direct methane losses (from storage, incomplete use or processing of the gas). However, the benefits of producing and using biogas are potentially becoming less clear. Globally, a shift towards cleaner forms of energy is making the displacement of energy using electricity derived from biogas less beneficial. Greater reductions of carbon were possible before when 'dirtier' forms of energy, such as coal were being displaced. Now, with cleaner energy mixes, these benefits are eroding. Despite this, direct losses of methane are still being seen. The wastewater sector is a major source of methane emission, contributing to 5--8% of global anthropogenic emissions (Ocko et al, 2021) and traditionally in the UK, open secondary digestion was common to provide additional destruction of pathogens from the wastewater. Recent measurements in the USA showing far greater losses of methane than previously believed (Vasquez, 2023). Methane has a global warming potential of 25 times that of carbon dioxide over a hundred-year period, but there has been emphasis in the industry to use a more realistic 20-year horizon, in which case it is 86 times worse. This means that leaks do not have to be large to offset the benefit of using the biogas in the first instance. For example, the digestion of sewage sludge can typically yield 350 m3 biogas/tonne solids fed to a digester. This is on average 65% methane, and based on its inherent energy, the biogas will have an energy content of 2,400 kWhr. After losses, a third of this energy could be used in an engine to offset fossil-fuel, i.e. 720 kWhr. This would displace 570 kg carbon equivalents of coal. A 1% loss of biogas, i.e. 3.5 m3 would contain 2.3 m3 of methane with a weight of approximately 4.6 kg. Using a 20-year horizon for methane, this has a carbon footprint of 396 kg. For a displacement of 570 kg carbon, therefore a loss of (576/396 =) 1.45% of the biogas would cancel the benefit of using the biogas. Figure 2 shows the contributing factors towards carbon footprint for the various stages on the carbon footprint of biogas used in co-generation, on the grid or as a displacement fuel for gasoline or diesel. This is only referring to the loss of methane. As mentioned, the sludge, biogas and liquid streams derived from biogas generation need processing and these also carry an environmental impact. This paper will go into detail into the processing impacts of biogas production and use, and compare that to the alternatives where digestion is absent, or organic materials are not digested but rather diverted to landfills, in order to provide a greater insight into the influence of anaerobic digestion on reducing carbon pollution. REFERENCES Ocko I. B.; Sun T.; Shindell D.; Oppenheimer M.; Hristov A. N.; Pacala S. W.; Mauzerall D. L.; Xu Y.; Hamburg S. P. 2021 Acting rapidly to deploy readily available methane mitigation measures by sector can immediately slow global warming. Environmental Research Letters, 16 (5). Vasquez, K. (2023) Wastewater treatment releases nearly double the methane that was previously thought, Chemical & Engineering News.

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

SpeakerBarber, William

Presentation time

08:30:00

08:50:00

Session time

08:30:00

10:00:00

SessionDrones, Satelites, Sensors, Oh My!: Advances in Fugitive Methane Monitoring

Session number11

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicBiosolids To Energy, Climate Change Mitigation, Energy and Carbon Neutrality, Greenhouse Gases, Odor/Air Emissions, Regulatory Requirements, Sensors, wastewater

Author(s)

Barber, William

Author(s)W. Barber1

Author affiliation(s)Cambi Inc, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159773

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count11

How Thermal Hydrolysis Influences The Economics Of Biosolids Management

Abstract

Thermal hydrolysis continues to gain in popularity around the world. There are over 120 facilities worldwide and several across the United States. In North America, operating plants range from approximately 10 to over 400 dry tons processed daily. DC Water's Blue Plains facility, the first in North America, has been operational since 2014. Whilst many studies have looked at the influence of the technology on biosolids management, virtually none of have been specifically focused on the detailed financial impacts. Furthermore, when costs are presented within biosolids master plans, they are inconsistent across projects and can have a wide variance. Financial drivers play a major role in decision making with respect to biosolids processing and generation of master plans. However, whilst important, the financial aspects of a project are multifaceted and involve numerous other influencing factors. These include, amongst others: basic cost of capital equipment (varies with supplier); impact and use of existing infrastructure (how much can be reused or repurposed); requirement for future investment (for example, will new digesters be required); contingency; liquor treatment; delays (in construction); standards/requirements, use of unions, incentives etc. From experience, financial impacts are also geographically dependent making global benchmarking of projects challenging. For example, costs are consistently lower in the UK, where it accounts for 50% of all the sludge produced, than they are in the US. Figure 1 shows the influence of plant size on normalized capital costs in the UK. Although a key component in many projects, it only contributes between 5 and 50% of the overall cost with the emphasis on the lower end. Figure 1 demonstrates economies with scale, becoming more cost effective as projects increase in size. However, modularization has reduced costs recently, making thermal hydrolysis cost effective at smaller sizes than previously possible. Thermal hydrolysis reduces the costs of sludge processing centers. It does this by increasing capacity of digestion, drying, incineration and composting. It is well documented that capital costs at Washington DC's Blue Plains facility fundamentally reduced due to thermal hydrolysis. However, depending on what infrastructure is on site, there additional investment in auxiliary equipment may be required. New research on reducing retention times in digestion by using thermal hydrolysis suggests that capital costs can decrease further. With current knowledge, the number of anaerobic digesters at Blue Plains could reduce further from 4 to only 2. saving a further $80M. Furthermore, construction influences overall costs, with delays adding to but also deferring from making cost savings. Additionally, plans for future expansion can be deferred, minimized, or eliminated altogether, as thermal hydrolysis can be installed as part of a step-wise program. Additional, due to the higher loading rates possible, capacity on existing digestion plants, can be used for the digestion of organic wastes with further influence on economics. From an operational viewpoint, more biogas is produced which can provide revenue, and a combination of enhanced anaerobic digestion performance with superior dewaterability result in significant reductions in biosolids cake resulting in cost savings. At Blue Plains, production of higher value biosolids has resulted in revenue from sales, and since installing thermal hydrolysis, DC Water are saving approximately $20M annually of which $15M is due to reduced biosolids production. Ongoing work is looking at reducing costs further by selling portions of the biosolids cake. However, sludge must be thickened prior to processing, energy is required for thermal hydrolysis to meet the heating needs, better digestion performance releases more nutrients which then need to be treated with chemicals and electricity. More infrastructure needs additional maintenance, and additional biogas needs to be processed further prior to use.
The aim of this paper is to look at the capital costs of thermal hydrolysis as well as the influence it has on both capital and operating costs of biosolids processing based on plant data and modelling. Several sensitivity analyses will be presented based on different configurations of the technology comparing it to a facility where thermal hydrolysis is absent, in order to show where the main influencing parameters are. These will also be compared to data available from various studies and actual cost savings. An example of the model is given in Figure 2. Which shows the typical operational breakdown of standard mesophilic anaerobic digestion compared with that preceded by thermal hydrolysis. Figure 2 is based on all sludge costs from thickening to biosolids recycling (to land, in this case) inclusive of the treatment of the liquors released by anaerobic digestion. For ease of comparison, costs are combined, i.e. electricity refers to electricity required by thickening, digestion mixing, pumping, downstream dewatering and liquor treatment. The figure clearly shows the influence of cake application costs, assumed here to be $45/wet ton. At that cost, cake recycling accounts for nearly 2/3rds of the entire biosolids processing costs. This reduces to approximately 40% with thermal hydrolysis due to the introduction of new parameters. After costs related to cake production, costs for liquor treatment are next most influential and can be up to a third of the whole operating cost. Although a great deal of focus is placed on the costs of maintenance and energy required for steam generation, these are much less significant than would otherwise be expected. Although more processing is being done with thermal hydrolysis, the running costs are between 70 and 80% of those without pretreatment. They remain lower due to the large reduction in cake production. When combining these reduced costs with increased revenue from biogas, the costs of running thermal hydrolysis with digestion are between 40 and 60% of those when there is no pretreatment.
This paper will look at adding additional processing steps, such as drying, (and partial drying with thermal hydrolysis and digestion â€“ Figure 3) and look at the specific impacts of adjusting the price of utilities such as polymer and gas. The impact of additional thickening prior to thermal hydrolysis to reduce heat requirement will be investigated to see if there is a financial benefit to thermally hydrolyze higher dry solids sludge in order to reduce steam consumption. The paper will show the impact of entire biosolids processing on overall costs. For example, full-scale experience in Europe has shown that intentionally making equipment underperform may result in operational cost savings. In addition, the influence of different uses of biogas, for steam generation, electricity production or biomethane will be determined. The influence of using natural gas or biogas for drying will also be reviewed by means of examples. In combination from various full-scale facilities, a number of normalized costs as $/wet ton will be presented along with suggestions on how to minimize the ownership costs of thermal hydrolysis.

Whilst decision making for biosolids management is complex and influenced by many parameters, financial considerations are of utmost importance. Thermal hydrolysis, a pre-treatment to anaerobic digestion, is gaining traction in North America due to its ability to change sludge properties altering performance of downstream processes. Higher loading rates and enhanced performance due to thermal hydrolysis means processes are smaller or can be optimized. Additionally, renewable energy is increased

SpeakerBarber, William

Presentation time

15:35:00

15:50:00

Session time

15:30:00

17:00:00

TopicIntermediate Level, Biosolids and Residuals, Energy Production, Conservation, and Management, Facility Operations and Maintenance

Author(s)

Barber, William

Author(s)Bill Barber1; Paul Christy1

Author affiliation(s)Cambi Inc., Malvern, PA1