GRAND RAPIDS, Mich. (WOOD) — The silo looking domes going up in the backyard of Grand Rapids’ sewage treatment plant are designed to turn the solid waste coming from restaurants and other food-related businesses into environmentally friendly money savers.

It a process, city leaders say, will save them from spending millions to expand traditional sewage treatment operation.

“That would have been much more expensive and would not have produced the environmental benefits and sustainability benefits that the digester will,” said Grand Rapids City Manager Eric DeLong.

The biodigester takes that waste and cooks it down to a more manageable form.

But as construction continues, the cost for things like steel, electronics and other items increased. So did the price of contractors.

“If you’re an owner or trying to do something in your home right now, you know contractors are very busy. It’s the same thing for us,” DeLong said.

And then there are add on options, like a more environmentally friendly gas recovery system.

 The various factors that have driven the expected cost to $85 million. 

And if you are a Grand Rapids sewer customer, you are likely going foot that bill.

Proposed sewer rates for Grand Rapids and several outlying communities on the system would increase 3.49%, or about $12 a year.

But by 2021, that increase could be as high as 11%.

The same unknowns that have driven up the cost of the project will play a factor in the 2021 increase.   

“By doing it over two years, we should be able to moderate the increase and have less than a total increase of 11 percent,” DeLong said.

The sale of gas and other byproducts should offset those rate increases, eventually.

But by how much and when maybe just as difficult to predict as the cost to build the biodigester.

For example, the city will sell off the renewable natural gas or RNS from the process.  

“Right now, the market is trending at less than $1 per unit of RNS. If that comes up, we will do much better,” DeLong said.

City commissioners are expected to take up the issue during their Dec. 17 meeting.