Resource recovery is becoming a focus worldwide, especially within the municipal wastewater industry. With climate change and high energy costs, the industry is taking a closer look at resource recovery opportunities that lie within wastewater, namely carbon. Wastewater’s carbon content represents a valuable and largely untapped source of energy.
Carbon converts to “green” energy, which is one of the keys to a sustainable future. Through effective use of wastewater’s carbon, in combination with other established renewable energy technologies, enough energy can be recovered so that the wastewater treatment plant could become energy-neutral, eliminating the need to import energy.
The City of Calgary’s 2016 Water Energy Management Strategy proposed an energy-neutral target by the late 2030’s for its Pine Creek Wastewater Treatment Plant, achieved by increased energy efficiency and energy recovery. This target was the main driver for the Pine Creek Energy Audit project, which was followed by several resource recovery studies.
The City engaged Associated Engineering to provide energy and resource recovery expertise to establish an energy-use baseline and identify capital and/or operational modifications to optimize energy use. The City sought to quantify “available energy” and identify opportunities for greater resource recovery to establish a roadmap to become energy neutral.
Project Manager, Shane Thompson, explains, “To establish an energy-use baseline, we analyzed the energy inputs and energy outputs, and then reviewed the available energy, primarily biogas.” The plant imports approximately 22 million kilowatt-hours of electricity and 33,600 gigajoules of natural gas per year, and also uses some of the produced biogas for heating.
Shane advises, “Moving a facility from the status quo to energy neutral involves consideration of energy efficiency, energy reduction, and energy recovery.” To improve energy efficiency, the team considered operational changes, such as control adjustments, that could improve energy efficiency without compromising treatment performance. We also considered upgrading to more energy-efficient equipment.
To reduce energy use, the team reviewed the treatment processes and compared them to less energy-intensive options, with the potential for improved biogas production. For example, we estimated the energy reduction potential of switching from a largely biological to a hybrid chemical phosphorus removal system.
For energy recovery, the team conducted an in-depth analysis of cogeneration, the process of converting gas to electricity and heat. We also considered enhanced biogas production; conversion of biosolids to biocrude oil, diesel fuel, or syngas; wastewater heat recovery; and solar power.
Achieving energy-neutral status at the Pine Creek facility is possible using established technologies
Subsequently, the team developed two energy-neutral roadmap examples, representing the “book-ends” of what might be possible. The roadmap examples demonstrate that energy-neutral status at the Pine Creek facility can be achieved without “core” technology changes, using simple technology retrofits, some of which are currently being further evaluated by The City of Calgary.
Our key personnel on this project are Shane Thompson, Dean Shiskowski, Jill Townsend, and Daniel du Toit.