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When Does Use of Waste Activated Sludge (WAS) Lysis Make Sense?

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With increasing number of municipalities across the United States facing the need to be more sustainable there is an increased emphasis on becoming less reliant on outside energy to operate their treatment facilities by creating energy onsite to meet most or all of their onsite needs. Maximizing the gas production from the anaerobic digestion process/ cogeneration is becoming an important strategy that is being evaluated and implemented by municipalities in the United States (and globally) in an effort to become more sustainable.

In trying to maximize gas production from biosolids, it is well known that the anaerobic digestion of WAS is a rate limiting reaction that restricts the recovery of biogas from WAS solids. Several technologies are in the market place that transform the WAS solids to more bioavailable form that has reported to increase the gas production and energy recovery. Table 1 lists some of WAS lysis technologies available currently and the number of installations globally. As observed in Table 1 below, there are more installations of these technologies outside the United States.

Table 1: Summary of Currently Available WAS Lysis Technologies
TechnologyLysis MechanismInstallations (US/Global)Achieves Class A?
CAMBIPressure and Heat(1/13)Yes
BiothelysPressure and Heat(0/3)Yes
OpenCELPulsed Electric Field(1/1)No
Crown BiogestPressure(0/18)No

Despite being in the marketplace for several years, there application in the United States does not show an increasing trend. Although its application in the United States is in part limited due to their relative infancy in the market place, there are also some frequently recurring questions regarding their viability that has in part limited their consideration in implementation. Some of these questions include:

Is the energy balance for WAS lysis process favorable? (i.e., does the energy input exceed the energy recovered?)

Does he additional cost for WAS lysis capital improvements outweigh the cost of increasing the solids retention time (e.g., with additional digester capacity) through other conventional methods?

Does WAS lysis viable if the objective is to minimize total solids disposed (i.e., no energy recovery driver?)?

If Class A biosolids was not an objective, is WAS lysis viable if used to maximize energy recovery only?

Is the life cycle cost of WAS lysis technologies more favorable compared to other conventional approaches (e.g., increasing solids retention time (SRT) using conventional digestion systems)?

Is the payback reasonable for implementing a WAS lysis system?

How does carbon footprint and green house gas reduction drivers impact implementation of WAS lysis technologies? Do they make them more or less favorable?

For what size treatment facility does it make sense to implement WAS lysis?

Having routinely encountered the above questions during the consideration of WAS lysis implementation with municipal stakeholders, the objective of this paper originated to share with the broader industry, responses to these questions that would allow the industry to identify when it would make sense for WAS lysis to be implemented.

Through the use of some case studies, this paper will provide insight into the above questions and considerations to evaluate the viability of WAS lysis. Only responses to some of the above questions are presented in this abstract. The paper to be submitted in support of this abstract will comprehensively address the remaining questions/ areas in more detail. In addition, this paper will also discuss a formal methodology that can be used to facilitate decision making on whether or not WAS lysis makes sense to implement at a given facility.
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Keywords: Anaerobic Digestion; Biosolids Master Planning; Cogeneration; Energy Balance; GHG; Recuperative Thickening; WAS; WAS Lysis; carbon footprint

Document Type: Research Article

Publication date: 2011-01-01

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