From The Editor | July 31, 2017

How To Get A Biodigester At Your Plant

Peter Chawaga - editor

By Peter Chawaga

There is no shortage of technology and equipment available to help wastewater treatment plants.

In fact, your average wastewater utility probably has a lengthy wish list of technologies that could help operations, efficiency, and safety. But these items are hard to procure, butting up against budget considerations, a litany of necessary approvals, and other strands of red tape.

The journey of one wastewater treatment utility, the Muskegon County Wastewater Management System in Michigan, offers others some lessons on how to approach technology upgrades. In this case, a new biodigester.

A Trip To Muskegon County

The Muskegon County Wastewater Management System has 42 fulltime employees serving approximately 130,000 residents. Its lagoon plant facility is designed for a capacity of 43 MGD, but currently receives only about 12 MGD of influent.

“Front end treatment starts with a 50-million-gallon full mix cell for removal of biochemical oxygen demand, followed by a 90-million-gallon aerated settling cell for removal of solids and metals, followed by a six-billion-gallon storage lagoon,” said Dave Johnson, the system’s wastewater director.

The plant sits on 11,000 acres, nearly half of which is crop land. From May through October, the water in the storage lagoon is pumped to 53 irrigation rigs and sprayed on corn, soybean, wheat, and alfalfa crops. Those plants absorb the nitrogen and phosphorus and the remaining water trickles through the soil, reaching drain tiles that carry it out to the Muskegon River.

In all, it appears to be a pretty tidy operation, one that has more than enough capacity to serve its customer base and that already employs a fairly sophisticated wastewater reuse program. But Johnson and his team saw a glaring opportunity to do even better.

The Muskegon County Wastewater Management System gets additional waste hauled in from nearby producers, things like septage, grease trap waste, food-processing waste, even blood waste. These contain a lot of untapped energy, which, with the right equipment, can be harnessed when the wastewater is processed.

“We were thinking about putting in a digester for this high-strength waste and getting some energy out of it by treating it anaerobically, rather than putting energy into it by treating it aerobically,” said Johnson. “We’ve been approached by a few companies that were interested in putting in a digester out here to utilize our hauled waste stream. The idea of turning waste into energy is attractive to us.”

Journey To Biodigestion

Musekgon’s wastewater system is fortunate in that the county commissioners and administrator strongly support energy-efficient initiatives. In addition to the cropland that already exists alongside the treatment facility, the system is exploring the potential to lease portions of its land for wind and solar development.

So, when the opportunity came to turn wastewater into energy, approval was swiftly granted and moving the project forward became a matter of determining how exactly it would work. To do that, the wastewater treatment plant would have to use Prein and Newhof, a regional engineering company with which it has a three-year contract.

“We brought a request before the Muskegon County Board of Public Works for having that engineering firm do a feasibility study on putting in a digester at our facility,” said Johnson. “There was unanimous support from the board.”

Though support from stakeholders is strong, the engineering firm will need to confirm some key variables before Muskegon will get its biodigester.

“Ultimately, we want to know whether it’s feasible given our waste loading, whether we have a suitable location for it, and whether we should pay for it and operate it ourselves and get all the benefits of the gas production, or have another company put up the capital to build it and operate it for a profit, with us getting only some of the benefits of the gas production,” Johnson said.

Johnson expects the feasibility study to be complete by October and an agreement stipulates that it cannot cost more than $38,000. If a biodigester is determined practicable, a different engineering firm would be commissioned to build and install it.

“If the feasibility shows that we should put up the money for the project ourselves and operate the digester, then we’ll do the design/bid/build approach,” Johnson said. “If the feasibility study shows that it’s more advantageous for us to let another company build the digester and operate it for a profit, then we’ll have to evaluate proposals and pick the one we feel is most advantageous to us.”

If Muskegon County does elect to install a biodigester at its wastewater treatment plant, which seems likely, it will still be another few years before it is operating. That is just another indicator of just how complicated it can be to make significant technological improvements to these delicate operations. But as Johnson and his team are betting, the effort can be well worth it.