Here Comes East Lansing’s Poop Digester

Above: a rendering of the digester.

There’s a big upgrade in the works for East Lansing’s Water Resource Recovery Facility (WRRF), the plant that treats wastewater for East Lansing, Meridian Township and Michigan State University. A new environmentally friendly “digester” is being added to the section of the plant which handles “biosolids,” the industry term for anything that goes into a drain or sewer that isn’t water.

In an interview with ELi, Bob Scheuerman from the City of East Lansing’s Engineering Department explained that there are two end products of the wastewater treatment system.

One end product is clean water, which is released into the Red Cedar River after going through a final disinfection process by being pumped through an array of ultraviolet lightbulbs.

The other end product is “biosolids,” which are currently “dewatered” in the plant and then dumped into a semi-trailer sized dumpster to be hauled off to a landfill.

When the new system comes online, the solids will be pumped into a silo-like tower where anerobic bacteria will get to work, digesting the solids and releasing methane gas which will be stored in a tank on the WRRF site.

A gas-powered generator called a Combined Heat and Power (CHP) unit will burn the methane, providing heat to keep the digester working efficiently and providing electricity to supplement the electric needs of the plant.

After the bacteria has done its work, the resulting sludge will continue to the dewatering process and the quantity of “solids” destined for landfill will be considerably less than the current quantity.

Between the savings in landfill costs and the reduction in electric costs, Scheuerman estimates that the digester will result in savings of about $500,000 per year.

This represents the third phase of an ongoing renovation to the WRRF, which was necessary to add treatment capacity as well as upgrades to worn equipment.

The work is being financed by a $33.5 million loan from the Michigan Department of Environmental Quality’s “State Revolving Fund” (SRF), which provides low-interest loans to Michigan communities in order to improve water infrastructure.

Because our WRRF serves Meridian Township and MSU as well as East Lansing, responsibility for loan payback is spread between all three communities. The digester and supporting equipment represent about $8 million of that amount.

The SRF program provides loan forgiveness (meaning a reduction in loan principal) for projects that include “green” infrastructure. Scheuerman told ELi that because of the digester, this project qualified for $2 million in loan forgiveness, “far and away the highest of anybody in the state.”

When plans began for treatment facility renovations in 2017, the need for a backup generator was identified as an important component to keep the facility functioning during a prolonged power outage, and to improve the operational resiliency of the WRRF.

This need opened the door to the possibility of a digester, since a CHP unit could perform the same function as a million-dollar emergency generator. Unlike an emergency generator, the CHP unit will operate all the time, thereby reducing utility costs while still providing the same emergency capabilities as a generator.

Initially, a larger-scale digestion system was considered, but it was not deemed cost-effective. After further analysis, engineering staff found that a smaller scale digester project could provide the desired efficiencies at about one-third of the estimated cost.

“Electrical rates are going to increase,” Scott House, Director of the Department of Public Works, explained, and landfills are becoming more restrictive.

“Should we be sending something to the landfill that we don’t have to?,” House asked, rhetorically.

He told ELi that the new design, which includes space for a second digester in the future, puts the facility in a better position to meet future regulatory changes. A second digester would mean that solids could be processed to a standard that would qualify them for “land application” (fertilizer), and it might eventually be possible to run the WRRF without sending any byproducts to the landfill.

Upgrading the solids-handling part of the facility also means an improvement in daily operations at the plant.

House explained that the current equipment is difficult to maintain since it is located on the second story of a building which is difficult to access. It’s also inefficient.

Currently, there is only space for one dumpster, which means that, when the dumpster is full, the entire system has to shut down temporarily while it is hauled out and replaced. This results in a backup of “solids.”

The new system provides space for additional dumpsters and loading flexibility.

Even if something goes wrong with the digester, staff will be able to reroute solids for dewatering and landfilling while work is completed to get it back on line.

“Right now, if something went down on this one, you just process everything like you already did and you just send more [to the landfill] for a few days,” said Scheuerman.

Construction of the new digester is scheduled to begin in April and is expected to be completed by January 2021.