More than 25% of the total operating costs of wastewater treatment plants (WWTP) are frequently related to the electricity cost of wastewater treatment. Sustainable energy is becoming more and more necessary, particularly in these treatment plants. Although there are numerous ways to combat wastewater treatment plant expenses, one of the most economical options is to invest in sustainable energy. This article will show wastewater biogas and how it can save energy for WWTPs.
What is biogas?
Biogas is an environmentally-friendly, renewable energy source produced by the breakdown of organic matter such as food scraps and animal waste. Biogas is a renewable fuel that is created when microorganisms break down organic materials, such food or animal waste, without oxygen. Anaerobic digestion is the term for this process. The waste material must be contained in an oxygen-free environment for this to happen.
Biogas can be produced purposefully as fuel in an industrial process or organically.
Beneficial as an energy source
Since the biological material used to make biogas will naturally decompose, it is less harmful to the environment to capture the gases created by this process and use them as a source of energy rather than letting them leak into the atmosphere.
In addition to being primarily cyclical, the biogas production process is part of a larger, sustainable cycle for managing agricultural waste. For instance, biogas can be created from the animal waste generated on a farm and utilized to power farm equipment.
A wide variety of waste material breaks down into biogas, including animal manure, municipal rubbish or waste, plant material, food waste or sewage.
Biogas consists mainly of methane and carbon dioxide. It can also include small amounts of hydrogen sulphide, siloxanes and some moisture. The relative quantities of these vary depending on the type of waste involved in the production of the resulting biogas.
What is cogeneration?
The term “cogen” refers to a fuel that is thermodynamically efficient. Cogeneration uses this thermal energy, but independent electricity production must discard some of it as waste heat.
For municipal WWTPs that currently have or intend to install anaerobic digesters, this is a dependable and affordable choice. The methane gas produced in these digesters can be used as fuel in a CHP system to provide the WWTP with dependable heat and electricity.
Benefits of a cogeneration system
Produces power at a cost below retail electricity.
Displaces purchased fuels for thermal needs.
May qualify as a renewable fuel source under state renewable portfolio standards and utility green power programs
Enhances power reliability for the plant
Produces more useful energy than if the WWTP were to use biogas solely to meet digester heat loads
Reduces emissions of greenhouse gases and other air pollutants primarily by displacing utility grid power
The EPA has a report of the technical and economical potential for cogeneration energy at wastewater treatment facilities right here. The analysis found that cogeneration/CHP is a strong technical fit for many facilities. It can also be a worthwhile investment for areas where local electricity prices are very high or unstable.
Real world success stories
Energy Trust has provided energy upgrades to four plants in the Portland metro tri-county area, which is home to roughly half of the state’s 4.27 million residents: the Columbia Boulevard Wastewater Treatment Plant in Portland, the Tri-City Water Resource Recovery Facility in Clackamas County, the City of Gresham’s wastewater treatment plant, and Clean Water Services’ Durham treatment facility.
Clackamas County
Energy Trust most recently worked with Clackamas Water Environment Services (WES) in Clackamas County, which uses their Tri-City Water Resource Recovery Facility to clean more than 11 million gallons of wastewater daily for more than 190,000 county households.
The facility was already converting waste materials into renewable biogas, but it was due for an upgrade after operating for more than 30 years and serving a much larger population. A new anaerobic digester tank was added since the two that were already there to handle biosolids were overflowing and not functioning well. Additionally, the original cogeneration engine was nearing the end of its useful life.
A new 600-kW lean-burn engine was attached to the digester tanks as part of the July 2021 improvements. Now, the engine’s excess heat from burning the methane is collected and used to heat the digesters and the surrounding area.
In addition to providing heat for five buildings on the property, the system is expected to generate 4,300 megawatts of power annually, which is roughly half of the facility’s energy consumption.
In the first year, we anticipate saving roughly $319,000 on electricity and $99,500 on heating. “Over the life of the engine, the average annual savings are expected to be about $619,000 on power and $191,000 on heat as our population grows and waste loads to the plant increase,” said Lynne Chicoine, capital program manager at WES.
Biomass in Oregon
The majority of biomass resources in Oregon are secondary products like logging slash, animal dung, and lumber mill leftovers, while there are a few crops specifically grown for biomass energy. Woody biomass, spent pulping liquor (a byproduct of the pulp and paper manufacturing process), agricultural field residue, animal manure, food processing residue, landfill gas, municipal solid waste, and digester gas from wastewater treatment plants are a few examples of biomass resources that are available in the Northwest.
There are 17 woody biomass power plants in Oregon, most of which are used in the wood products sector. Schools and hospitals are among the 21 other establishments in Oregon that use woody biomass to heat their spaces.
Conclusion
Wastewater biogas presents a sustainable and cost-effective solution for wastewater treatment plants (WWTPs) to reduce operating costs and enhance energy efficiency. By harnessing the power of anaerobic digestion, WWTPs can transform organic waste into renewable energy, significantly lowering electricity expenses and minimizing environmental impact. The integration of biogas cogeneration systems further optimizes energy production, making wastewater biogas a vital component in the pursuit of sustainable energy practices in wastewater management.
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References
What is biogas?
https://www.nationalgrid.com/stories/energy-explained/what-is-biogas
What is Cogeneration and How Can It Save Your City’s Wastewater Budget?
Bioenergy
https://www.oregon.gov/energy/energy-oregon/pages/bioenergy.aspx
Tri-City Water Resource Recovery Facility
https://www.clackamas.us/wes/resource-recovery-facility
