Proceedings

A US perspective on alternative uses of thermal processes

Burrowes, P., Williams, T. and Lukicheva, I., CH2M, Canada

(free)

Abstract:

More than 7 million dry metric tons (dt)of sludge are produced in the United States (U.S.) annually,
While the regulations in Europe drive towards energy efficiency, greenhouse gas reductions and landfill
diversion of carbon, due to high energy prices and limited land availability, the regulations in the U.S.
encourage agricultural land application and incineration, given that energy costs are low and land is
available. Notwithstanding, public opposition to land application, rising costs and recent incineration
emission regulations have resulted in many municipal utilities looking beyond the tried and true
practices of anaerobic digestion (AD) and land application or incineration and considering technologies
that will reduce volumes to be utilised and recover maximum energy.

The paper presents a description of the state of sludge management and work being carried out in the
U.S. This includes further processing of both digested and undigested sludge using various thermal
processes including gasification and pyrolysis. Each is in different states of development and has the
potential for different end products and environmental benefits. The paper analyses several process
train scenarios using actual wastewater plant data to illustrate the energy balance of these further
thermal processing technologies, and compares life cycle costs.

Introduction:
More than 7 million dt of sludge are produced in the United States (US) annually, while more than 10
million dt are produced in the Europe Union. When comparing land areas and populations, the US
occupies about 9.8 million square kilometres (km2) with a population of about 326 million, while Europe
occupies about 4.4 million km2, with a population of about 508 million. Currently, the drivers for
managing sludge in the U.S. are different to Europe. While the regulations in Europe drive towards
energy efficiency, greenhouse gas reductions and landfill diversion of carbon, due to high energy prices
and limited land availability, the regulations in the U.S. encourage agricultural land application and
incineration, given that energy costs are low and land is available.

Notwithstanding, public opposition to land application, rising costs and recent incineration emission
regulations have resulted in a paradigm shift to resource recovery. Many municipal utilities are looking
beyond the tried and true practices of anaerobic digestion (AD) and land application or incineration and
considering technologies that will reduce volumes to be utilised and recover maximum energy and other
resources. There is also a move towards wastewater treatment plant (WwTP) energy neutrality. The
foregoing looks at the trends and analyses the energy recovery opportunities from this paradigm shift
to resource recovery.

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