Clearing the air

Landfills are a cost-effective solution for dealing with municipal solid waste (MSW). However, the liquid and gas byproducts generated at these dump sites must be painstakingly monitored to ensure that harm to the environment is minimized. Landfill gas (LFG), which is a natural emission stemming from the decomposition of organic landfill waste, consists of approximately half methane and half carbon dioxide (CO2). Together, these landfill-generated gases are a major source of greenhouse gas emissions throughout the world.

While the city of Toronto emphasizes a comprehensive integrated waste management strategy that prioritizes waste reduction, reuse and diversion, minimizing the footprint of its Green Lane Landfill is top of mind for operators.

Inside Green Lane

The Green Lane Landfill was purchased by the city of Toronto in 2007. Formerly a small local landfill owned by the private sector, Green Lane has expanded to a site area of 129.7 hectares (about 320 acres), of which 71.2 hectares (about 175 acres) is approved for landfilling. Through rigorous monitoring and oversight, the city’s Solid Waste Management Services staff aids in limiting the environmental effects of the landfill to help promote a safe, long-term solution to handle the city’s waste through its estimated 2040 close date.

Green Lane Landfill currently features a hydraulic trap, leachate collection system, leachate treatment plant, LFG collection system, enclosed flares and stormwater control system to protect the site from environmental harm.

LFG is collected from 170 vertical and 68 horizontal collection wells and 9 manholes located at the site. Approximately 75 to 80 percent of the current landfilling area includes vertical and horizontal landfill gas collection wells and subheader and header pipes, which convey LFG to three enclosed flares.

“Vertical landfill gas collection wells are installed in locations that have been filled to final elevations alongside slopes and at the surface of the original landfill and interim expansion area,” says Grace Maione, the acting director of processing and resource management for Toronto’s Solid Waste Management Services Division. “Horizontal LFG collection wells are installed as landfilling progresses with the first trenches installed at least 6 meters (about 20 feet) above the landfill base. LFG is also collected from leachate collection system manholes. Blowers at the flares pull landfill gas from subheader pipes connected to the wells to a larger perimeter header pipe that runs along the north and south limits of the landfill. Condensate traps are located at low points in the system to collect moisture from the LFG, and collected condensate is sent to the leachate treatment plant.”

Overall, Maione says that approximately 4,300 standard cubic feet per minute (SCFM) of LFG is collected at the site, which is equivalent to more than 60 million cubic meters per year. This LFG is incinerated in three enclosed flares and a fourth flare is planned for the near future.

Monitoring the site

Green Lane staff is tasked with monitoring and analyzing complex LFG data generated from the site and works to make modifications as needed to maximize collection efficiency.

“The landfill gas management system includes flow meters at each flare and an analyzer that continuously monitors the methane and oxygen content in the main gas header,” Maione says. “The gas analyzer is calibrated according to the manufacturer’s recommendations and the city is notified of results. Values are communicated in real time to the operator though the SCADA (Supervisory Control and Data Acquisition) system. The engineer also collects a landfill gas sample annually, which is sent to an independent laboratory for testing. The pressure, methane, oxygen, non-methane organic compounds (NMOC), carbon dioxide and carbon monoxide results are tested and reported in [Green Lane’s] annual report.”

Green Lane’s staff works to maintain appropriate vacuum at the gas capture sites while limiting the amount of oxygen that is drawn into the system to prevent the risk of fires. Temperature and carbon monoxide levels are also scrutinized to ensure that the system is performing as designed.

One staff member is dedicated to monitoring the landfill as part of Green Lane’s engineering oversight. This staff member spends two to three days collecting the data from the wells in the field and then two days writing inspection reports and communicating findings in monthly meetings.

“LFG management requires monitoring of the overall and individual flow rates, pressure, quality and temperature at the wells,” Maione says. “Operations staff regularly monitor flow and percentage of methane and oxygen at each well to ensure the optimum vacuum is applied to the well field to maximize LFG capture and minimize odor. The contracted engineers also monitor gas flow, temperature and content at each well, manhole and at the flares, and [they] check on the condition of valves, sampling ports, flex hoses and settlement at the collection points. Immediate feedback is provided if necessary, and monthly meetings are held with the contractor, engineer and city to discuss observations and potential adjustments to the well field and system.”

To keep the system working as intended, Green Lane’s operations, maintenance and construction contractor currently employs two Technical Standards and Safety Authority (TSSA)-licensed operators to oversee the LFG management system. According to Maione, construction is carried out by their subcontractor using crews that include a construction manager, project administrator, construction supervisor and heavy equipment operators, laborers and health and safety representatives.

Maione says that Green Lane’s LFG collection system is aggressively advanced each year to maximize the capture at the site. This is made possible by the continuous installation of horizontal and vertical collection wells and sub-header pipes as needed.

Photos provided by City of Toronto

Breath of fresh air

Since LFG began being collected at Green Lane in 2004, significant progress has been made in reducing greenhouse gases. Maione says that in 2017, the site’s methane emissions were reduced by the CO2 equivalent of 414,301 metric tons.

Along with reducing greenhouse gases, LFG collection and diversion practices at the site have helped improve air quality in the surrounding area. Maione says that the city retained the services of a third-party consultant in 2012 that specializes in odor surveys and assessments. After a written odor abatement plan was drafted by the agency, Green Lane staff went to work to implement the best practices in 2013 and 2014.

“Refuse-related odors have since been reduced by the planned development of protected and screened active disposal areas, the reduction of the size of the daily working area and the progressive elimination of most waste types requiring special handling by receiving trenches,” Maione says. She adds that additional interim cover was applied to many areas of the site, which is a method the organization uses to control odor in areas that produce more landfill gas. For additional odor control, Green Lane also makes adjustments to the landfill gas collection field to draw more gas from higher production areas, as well as adjustments to the active landfilling area so that additional cover can be placed strategically.

Next steps

Although Toronto is not currently converting landfill gas at Green Lane to renewable natural gas (RNG), the opportunity is there to utilize this waste byproduct for energy. Green Lane has been identified as one of four area sites with RNG production capabilities by the city. However, changes in the city’s government following a recent election have led to uncertainty as to the future market for these renewable energies.

“Recognizing there are significant changes coming at the provincial and federal levels of government when it comes to renewable energy, coupled with an emerging renewable natural gas market and potentially a renewable fuel standards program in Canada, the city’s strategy today is to capture and convert biogas/landfill gas to RNG and inject it into the natural gas distribution grid,” Carlyle Khan, director of infrastructure development and asset management for Toronto’s Solid Waste Management Services Division, says. “Once in the grid, the city’s options in terms of its end use are numerous, with the base case being use in our Solid Waste Management Services fleet. There is an environmental benefit from moving the Solid Waste Management Services fleet from diesel to natural gas, and further by moving to RNG. The optimal scenario from an economics perspective is still developing.”

Khan says that although the city is waiting to see how public policies influence the demand for LFG technologies in the near term, Green Lane Landfill plans to play a pivotal role in helping Toronto better reach its civic goals in the decades to come.

“Renewable natural gas has the potential to offset electricity consumption behind the meter at Green Lane Landfill and be used in heavy-duty natural gas vehicles and equipment, but the real value comes from a triple bottom line considering the social, environmental and economic benefits once federal and provincial policies and programs are set and the emerging RNG market matures.”

The author is the editor for Waste Today and can be contacted at aredling@gie.net.