$68m Dry Anaerobic Digestion Cutting GHG Emissions by 49,000 TPA

IN DEPTH: Closing the Loop on Organic waste in British Columbia

A new fully integrated closed loop organic waste facility featuring dry anaerobic digestion and in-vessel composting has opened its doors in Surrey, British Columbia.

Dutch firm WTT was the turn key technology provider for the facility and was responsible for the delivery and installation of all biological process equipment and the entire odour abatement system.

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A new fully integrated closed loop organic waste facility featuring dry anaerobic digestion and in-vessel composting has opened its doors in Surrey, British Columbia.

Owned by the City of Surrey, the facility has been established via a Public-Private Partnership with UK based Renewi. Under the deal, the Government of Canada put up 25% of the $68 million cost of the plant and Renewi, which will operate the facility for the next 25 years, the remaining 75%.

Officially opened on 9 March this year, the City claims it to be the largest such closed loop organic waste plant operating in Canada. It will convert kerbside organic waste into renewable biofuel to fuel the City’s fleet of natural gas powered waste collection and service vehicles. Excess fuel will go to the new district energy system that heats and cools Surrey’s City Centre.

“The Biofuel Facility will be instrumental in reducing community-wide greenhouse gas (GHG) emissions by approximately 49,000 tonnes per year, which is the equivalent of taking over 10,000 cars off the road annually,” explains Mayor Linda Hepner. “This reduction in greenhouse gas emissions will also completely eliminate the City of Surrey’s corporate carbon footprint of 17,000 tonnes per year.”

The facility has the capacity to process around 115,000 tonnes of organic waste and produce approximately 120,000 Gigajoules of renewable natural gas and produce approximately 45,000 tonnes of compost annually. However, it was built with future-proofing in mind as the City currently collects approximately 65,000 tonnes of organic waste per year.

Technology
All Organic waste delivered to the Biofuel Facility will be treated “in-vessel”, meaning that 100% of it will be contained and processed inside the facility. The dry anaerobic digestion process uses anaerobic bacteria to produce biogas. The organic materials are sealed inside specially constructed anaerobic digestion tunnels fitted with airtight doors.

A bacteria-rich percolate mixture which includes inoculants, liquids leached from organics during the anaerobic digestion process, and oils and fats recovered from commercial food operations, is sprayed onto the new material in the tunnels. This activates the biogas production process.

Humidity and pressure is continuously monitored. Once the process, which takes 21 – 28 days, is complete, the raw biogas is transported to the adjacent Gasholder.

Gas Upgrading
Before the biogas, which is mixture of approximately 60% methane (CH4), 39% carbon dioxide (CO2) and trace contaminants, can be used to fuel the collection vehicles or injected into the grid, it undergoes an upgrading process.

This process produces a renewable natural gas (RNG) fuel that is interchangeable with natural gas and can be injected into natural gas distribution grids or used as vehicle fuel.

To achieve this the facility features water scrubbing technology. To begin, the raw biogas is compressed and fed into a Scrubber. Inside the Scrubber, the biogas is showered with water. This process captures the methane (CH4) and washes out the CO2 and other impurities. Any methane not captured in the Scrubber is “flashed off” in the Flash Tank and recovered.

The ‘sparkling’ water from the Flash Tank is pumped into a Stripper where the CO2 is released from the H2O. The clean water circulates back into the Scrubber and the CO2 is recovered for use elsewhere in the facility. The clean gas is then dried and injected into the grid. The scrubbing system was supplied  by Greenlane Biogas, a global specialist in biogas upgrading solutions with offices in Burnaby.

Composting
The facility also features in-vessel composting. A mixture of fresh organic waste, digestate from the AD process, and inoculants, is placed in enclosed composting tunnels fitted with specialised spigot aeration systems. The tunnels are sealed with an airtight door. The inoculants are collected from previous composting cycles.

Temperature, humidity and pressure levels in the tunnels are continually monitored to create the ideal conditions for microorganisms to complete the composting process. If oxygen levels drop, the aeration system injects fresh air up through the material to increase the oxygen level.

According to Renewi this ensures that no anaerobic spots develop. At the same time, humidity levels are controlled by a leachate system that sprays water down onto the composting material.

Under these optimised conditions microorganisms convert the organics into compost in a process that takes two to three weeks. After the composting process in the tunnels is complete, it is moved from the tunnels to the refinement section, where the material is separated into compost, inoculant materials and oversized fractions.

The oversized fractions mainly consist of plastics that can be converted into a Solid Recovered Fuel (SRF).

Award Winning
In March this year the facility became the most recent recipient of the Institute for Sustainable Infrastructure (ISI) Envision Platinum award. The Envision rating system rates sustainable infrastructure across the full range of environmental, social, and economic impacts.

The Surrey Biofuel Facility is the first waste sector infrastructure project in North America and only the third Canadian project overall to earn the prestigious Envision award for sustainability. The ISI Envision system measures sustainability in five categories: Quality of Life, Leadership, Natural World, Resource Allocation, and Climate and Risk.

These key areas contribute to the positive social, economic, and environmental impacts on a community. The Surrey Biofuel Facility earned high scores in the Leadership, Climate and Risk, and Natural World categories.

The facility also includes an Education Centre and an outdoor interpretive compost garden that will be used for conducting school and group tours.