If you’re looking to get into the business of turning food waste into easily-transported slurry, now is a good time, and the anerobic digestion products of biogases and nutrient-rich digestate hold untapped value. These are among the insights of four seasoned professionals in the realm of food waste anaerobic digestion (AD) who made up a panel for NEBRA’s Northeast Digestion Roundtable earlier this year.

Anaerobic digestion is well established as a means of stabilizing organics and reducing their volume, and it is increasingly being employed in the North East region. At the Northeast Digestion Roundtable in April, panelists talked about what’s currently standing in the way of expansion of food-waste AD and co-digestion, and the ripe opportunities for pushing beyond these barriers.

In Hermitage, Pennsylvania, at a water resource recovery facility with a digester for wastewater sludge and food waste, the hydrolysis tank is the first bottleneck. “We extremely underestimated how much holding capacity we would need back in 2008 when design took place,” said Thomas Darby of the Hermitage Municipal Authority. “If I had it to do over again, I would have had a separate, on-site facility with just depackaging equipment going into a tank – a much larger tank – that could then be used to feed the hydrolysis tank on a daily basis,” Darby said.

Transportation is a challenge too. Hermitage Municipal Authority gets offered food waste that it can’t accept because the offering entities “have no way of getting it to us,” Darby said. In Massachusetts, most of the anaerobic digesters are on farms in the central and western parts of the state whereas food waste is most concentrated in the eastern part of the state, according to panelist John Fischer of the state’s environmental protection agency. Fischer said the agency has seen some interest in intermediate processing facilities. Another panelist, Nat Harris, from organic-waste hauler The Compost Plant in Rhode Island, said the company has recently built a slurrying machine “so we have the ability to go further afield with what we’re collecting and have a little more control over our feedstock as we collect it.”

Another bottleneck for the Hermitage Municipal Authority is at the stage of generating power from digester gas. The facility is limited in how much power it can produce by a 500-kW transformer owned by a local energy company. Darby said Hermitage has two engines that it could run simultaneously but, “At the moment we have to throttle one back so that we’re under that 500-kW limit.” 

On the bright side, panelist Brett Reinford, owner a dairy farm in Pennsylvania called Reinford Farms, said the farm bought “hardly any” commercial fertilizer last year to grow corn and hay. That’s because the dairy and meat food waste the farm uses in co-digestion makes the digestate nitrogen rich. Reinford offered a tip to Darby, “I don’t know what the nitrogen or nutrient content of your solids are, but they could have some value to somebody.”

For entities looking to get rid of or accept food waste for anaerobic digestion, “matchmaking” is among the AD-related services of the Center for EcoTechnology (CET), which gave a short presentation about its AD resources at the April Northeast Digestion Roundtable. CET also has no-cost guidance documents on AD topics such as depackaging and source-separation technology.

NEBRA has hosted the Northeast Digestion Roundtable meetings since April of 2016. The meetings, which take place quarterly online, are free and open to all. NEBRA sponsors the meetings to share technical/operations experiences and to advance best practices in anaerobic digestion. Each quarter there is usually a technical presentation on a specific aspect of AD followed by lots of questions and discussion. NEBRA’s website has recordings and slides from past Northeast Digestion Roundtable meetings, including one on the food waste co-digestion start-up experience of the Greater Lawrence [Massachusetts] Sanitary District, and another on vetting feedstock “from both an engineering/design and implementation/operational perspective.”