BioCycle Magazine

Equipping Digester For Feedstock Flexibility

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Courtesy of BioCycle Magazine

Bayview Flowers is a high value, greenhouse floriculture operation in Jordan Station, Ontario, Canada, that supplies wholesalers and retailers across North America. In 2007, the company installed an anaerobic digester (AD) plant to generate 250 kW of renewable energy. The system was installed to take advantage of a province-wide Feed-In-Tariff (FIT) incentive program to increase the amount of renewable energy in the supply portfolio, as well as encourage farmers to further treat manure to reduce pathogens and odors. The Bayview digester was designed to process clean organic feedstocks such as grape pomace from the Niagara wine industry, off spec pet food and dairy manure. It is classified under Ontario regulations as a farm-based digester.

Over time, however, local supply and demand dynamics made it very difficult for Bayview to find clean, preconsumer organics. To remain competitive, the facility needed the ability to receive a wider range of materials as well as to show some market differentiation to waste haulers. This required: 1) Implementation of a pasteurizing system to meet a higher standard of regulatory requirements; and 2) Installation of contaminant removal equipment to reduce digester downtime and produce a digestate suitable for land application.

Clarence van Staalduinen, president of this second generation, family-owned and operated greenhouse floriculture business, and manager of the biogas plant, worked with Yield Biogas Inc. to implement the system design changes. Yield Biogas, through its Dr. Digester operational support services, had been assisting Bayview with feedstock evaluation, sourcing and biological support (e.g., supplying trace elements to keep microbial populations functioning properly), thus was very familiar with the plant, as well as the provincial organics waste supply chain.

Supply And Demand Dynamics

Ontario has been in a hyper-competitive supply and demand marketplace for organics because of the high density of processing facilities ranging from composting operations to biogas plants, and the absence of provincial regulations requiring diversion of organics from landfills. Additionally, preprocessing or contaminant removal capability is currently limited to only a few digesters; waste services companies have not set up preprocessing facilities (as of July 2016).

Farm-based ADs have been the most disruptive to the organics marketplace since they have the lowest capital and operating cost structure, and therefore can charge the lowest tipping fees to process the organic waste. Yield estimates that at present, municipal, commercial and farm-based anaerobic digesters in Ontario represent about 500,000 metric tons (MT)/year of commercial organic waste processing capacity. This estimate is determined by adding up all existing AD facilities in Ontario and the amount of waste they are permitted to process. (Detailed plant information can be found on is available on the Canadian Biogas Association’s website.)

There are variations in permitting between the sites as well as a wide variation in their designs. Digesters in Ontario don’t all have the same technical or operational capability to process the same types of organic waste. All ADs in the province utilize continuous stirred tank reactor (CSTR) type designs.

Technology And Design Options

The original design of the 250 kW Bayview biogas plant, built by PlanET Biogas Solutions, consisted of a 1,000 cubic meter (m3) primary digester, and a 1,000 m3 secondary vessel with insulation and a double membrane roof. The primary fermenter is a standard agricultural type design with paddle and submersible mixers, dry feeder, liquid manure feeding, but no pasteurization step. The secondary tank has one mixer, and was not plumbed for heating. The original feedstock mix was (approximate amounts) — on an annual basis — 4,000 MT of grape pomace and tulip bulbs, 2,000 MT of dairy manure, and 1,000 MT of off spec pet food.

Read the full article in BioCycle Magazine

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