New process from Greenfield Global could make anaerobic digestion faster and more economical

It is estimated that Canada’s wastewater treatment plants produce as much as 660,000 tonnes of dried sludge in a year. While a portion of the sludge may be treated and recycled as fertilizer, most facilities dispose of the remainder through landfills or incineration, placing a strain on their operating costs as well as on the environment.

Anaerobic digestion is an effective way to reduce organics, including sludge, by converting it to biogas. In some municipalities, anaerobic digestion happens at the wastewater treatment facility. In other cases, dedicated anaerobic digestion facilities are built to manage organics such as food waste. Overall capacity is currently limited, while the volumes of sludge and other organics grows.

But some Ontario companies are working on ways to boost the potential of anaerobic digestion and increase its adoption by municipalities.

Companies like Greenfield Global, Canada’s largest ethanol producer. Seeking a cost-effective way to deal with organic waste from its ethanol production, Greenfield’s engineers believe they have developed a solution that makes anaerobic digestion faster, more efficient and more economical.

Through a partnership with Ryerson University facilitated by the Southern Ontario Water Consortium (SOWC), they hope to prove that what’s worked for ethanol production will translate to wastewater treatment—with benefits for both the industry and the environment.

From stillage to sewage

To produce ethanol, corn is heated and fermented to convert the starch into ethanol. The remaining organic material is used to produce distillers’ grains which is sold as a high-protein cattle feed. But while the market for distillers’ grains tends to rise and fall, the cost of energy to produce it only rises.

In 2010, Greenfield faced the dual problem of low market price for distillers’ grain and increasing energy costs. In response, the company began investigating the use of anaerobic digestion to produce methane from thin stillage (the liquid by-product of its process) to power its Chatham plant.

In the course of incorporating anaerobic digestion, the company developed a two-step process combining a first stage continuously stirred tank reactor (CSTR) and a second stage fluidized bed reactor (FBR) that breaks down solid material much faster and more thoroughly than was previously possible. With less waste and increased capacity, the entire methane production process becomes much more cost-effective.

Once they’d established the effectiveness of their process in-house, Greenfield began to look at other applications for its new technology. Municipal waste disposal seemed a natural fit.

“Our thin stillage is about 4 to 4.5 per cent suspended solids; waste-activated sludge coming off a primary settler ranges between 2 and 4 per cent,” explains Dave Salt, Greenfield’s Vice President, Corporate Engineering. “So, we believe our technology will easily handle waste-activated sludge.”

“We’ve been getting very high solid destruction, up to 40 per cent” he adds, “which means our process could reduce municipalities’ disposal costs dramatically.”

But there was a problem in making the leap from stillage to sewage.

Greenfield’s engineers expect that both sludge and organic waste will work well as feedstock for their system. But they’re unable to test these materials on-site because the company is not a licensed waste processor. The need to connect with a research facility with the expertise to handle these materials brought them to SOWC.

Smaller footprint, higher capacity

SOWC staff connected Greenfield Global with Elsayed Elbeshbishy, Associate Professor of Environmental Engineering at Ryerson University and a respected researcher in the field of municipal waste management.

The result of their connection was a research project funded by SOWC’s Advancing Water Technologies program, which is supported by the Federal Economic Development Agency for Southern Ontario (FedDev Ontario). Based in Elbeshbishy’s lab at Ryerson, the project will accomplish two goals: first, test the Greenfield system’s ability to break down both municipal sludge and plant material versus thin stillage, and second, evaluate three different types of sludge for potential use as feedstock.

The results so far have been promising.

“Most of the cases using attached biomass systems like this can only process industrial streams or wastewater with low solid concentrations,” says Elbeshbishy. “To validate this system for high-solid waste is a big achievement.”

Aside from the improved rate of solids destruction, the Greenfield process has also dramatically decreased the length of time required to break down solids.

“In a conventional suspended solid system, the first stage requires a very long hydraulic retention time (HRT) of three to five days,” says Elbesbishy.  “Then the second stage can take between 20 to 30 days. But Greenfield has developed a fast biomass system with a much lower HRT. We’re talking hours instead of days in the first stage and four days instead of 20 in the second stage.”

Because the second stage uses smaller fluid bed technology rather than continuous stirred reactors, the Greenfield process requires much less space than conventional systems. This means it can be easily incorporated into existing equipment, an important consideration for municipalities.

According to Salt, “a smaller footprint and higher capacity significantly reduces the capital cost of building the digester.”

Opening communication channels

Positive results from this research will move Greenfield’s process closer to commercialization. But that’s not the only positive outcome of the partnership between the ethanol producer, Ryerson and SOWC.

Staff at both Greenfield Global and in Elbeshbishy’s lab have built connections with other researchers and industry partners through SOWC-sponsored technical sessions, workshops and leadership forums like Getting to Net Zero.

“These events have really opened the gates for us to collaborate, to understand what other people are doing, to feel that we are all working on the same problem,” notes  Elbeshbishy. “No other funder does this.”

“Our association with SOWC has opened up communication channels for us,” Dave Salt adds. “Waste treatment is a new industry for us but Rahim Kanji (SOWC’s Manager, Industry Partnerships) has introduced us to key players and this is helping us keep abreast of activities in the field.”

“Eventually, we’ll need to test our system at a wastewater treatment plant and run on real waste material. We hope to find an industry partner who’s willing to offer a host site for a demo-scale reactor, or even a small commercial-scale reactor.”

“Through SOWC, we’ve connected with people who might not have talked to us otherwise.”

2018-06-25T13:56:11+00:00 June 25th, 2018|Features|0 Comments

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