Egg-shaped tank to solve sludge problem at Holland wastewater plant

In about three years, the landscape of downtown Holland’s riverfront will have a new feature. It looks like a giant metal egg, and it will help Holland’s wastewater treatment plant solve a growing problem — getting rid of sewage sludge.

The egg-shaped tank is called an anaerobic digester. Sealed to keep out oxygen, inside the tank microorganisms that thrive under those conditions “eat” the sludge — the solids that are removed from the water during the wastewater treatment process — and produce gas.

This digestion process should alleviate the Holland Board of Public Works’ (HBPW) problem — it’s getting harder and harder to dispose of the sewage sludge produced by the plant.

The two disposal methods HBPW uses — depositing it at a landfill and using it to fertilize farmland — are both growing increasingly expensive and difficult. Some landfills aren’t taking the solids any more or are placing limits on how much they can take due to the high water content. A number of factors, including competition from other fertilizers, have made finding farmland that will take the treated biosolids more challenging.

The cost of disposing in a landfill has risen 200 per cent over the last 10 years, according to HBPW, and is expected to grow again by 30-40 per cent next year.

Using anaerobic digestion at the wastewater treatment facility is expected to cut HBPW’s disposal costs and have a positive environmental impact, with less waste being produced and the opportunity to use the gas that is produced as a source of renewable energy.

The egg digester’s process of converting sludge to gas cuts down on the amount of solid waste the plant has to dispose of by as much as 40 to 60 per cent, according to Theo VanAken, superintendent of the Holland Area Water Reclamation Facility. The gas can be captured and used to power electricity and heat.

“Currently, there is no better way to reduce biosolid volume while at the same time creating a renewable energy source using wastewater product,” VanAken said.

In addition, the solids that are left over after the digestion process are “higher quality” and can be used for broader applications such as fill dirt and nutrient-rich fertilizer.

The project is estimated to cost $23 million. HBPW has applied for a state revolving fund low-interest loan from the Michigan Department of Environment, Great Lakes and Energy (EGLE). The project also may qualify for a Green Project Reserve principle forgiveness program.

Aside from those environmental and financial benefits, VanAken said it’s also expected to reduce the odour produced by the wastewater plant.

It will, however, be an “imposing” structure, according to HBPW general manager Dave Koster, to add to the downtown area.

“Holland Energy Park is imposing as a structure too … but what we did with Holland Energy Park is we embraced it. We embraced it from the standpoint of making it a destination and an educational opportunity, and I think we have a similar opportunity with this too,” Koster told the Holland City Council Wednesday.

There are plans for educational signage, for example, about the digester and what it does.

New York City, for one, offers Valentine’s Day tours at one of its Brooklyn wastewater treatment facilities, including views of the city from an observation deck above its digester eggs.

The City of Grandville also has an egg-shaped digester. Other wastewater facilities in the area use other digester models, but the egg is ideal for locations that have space constraints, according to Koster.

The current timeline is to bid out the project next summer, begin construction in August 2020, and complete the project in 2022.

HBPW plans to follow the Envision framework, a set of sustainable infrastructure design principles from the Institute for Sustainable Infrastructure, in the construction of the facility.