Mackinac Island plans to convert its horse manure and sewage treatment sludge to electricity and use the heat byproduct to grow vegetables under a plan that was explained by the Board of Public Works (BPW) Wednesday, July 28, at a city council meeting.

The project, already underway, would convert horse manure and sewage plant sludge to methane gas, which would then be used to generate electricity. The electricity would power the Department of Public Works (DPW) operations, and excess heat from the conversion process would warm a year-around greenhouse.

“I think it is a really good plan,” said BPW Chairman Tom Lewand, who has been putting it together.

The $3.5 million plan will be added to a $7 million project to renovate the wastewater treatment plant. Recycling the sludge through the digester so it doesn't have to hauled to a mainland landfill is expected to save about $90,000 in shipping costs, and the byproduct from the digester can be composted. The electricity to be generated will save the DPW another $100,000 a year on its $150,000 electricity bill.

A verbal agreement to purchase the generated electricity has been negotiated with Cloverland Electric, which supplies the Island's power, said Mr. Lewand.

The projects, however, come with a price tag for sewer customers, who will face a 7% increase for each of the next five years beginning in April 2011. The compounded rate hike amounts to 40.3% by 2015.

“We've got to bite the bullet for higher rate increases now, but once we do, we're good for 15 years,” Mr. Lewand said, speaking of the improvements to the wastewater treatment plant.

Average year-around residential sewer users can expect to see a $35.77 increase in 2011, while seasonal users will pay an extra $16.03 the first year.

About 80% of the Island's yeararound residents, or 105 households, are not hooked into the sewerage system, said Mr. Lewand, and will not be affected. Many of them are in Harrisonville.

The city council will not be asked to approve the rate increases until later this year or in early 2010, he said.

To finance the projects, the DPW plans to sell $2 million in bonds at 3.25% interest and is seeking two grants from the U.S. Department of Agriculture totaling $2.5 million.

The proposed 7% annual rate increases for five years will raise $5.5 million and the DPW will chip in $500,000 from its savings.

If the city gets the grants, and there are no guarantees that it will, improvements to the wastewater treatment plant and the construction of the biodigester could begin next year.

Another increase will be seen in solid waste disposal. That operation, which collects, composts, and recycles rubbish, is operating at a $160,000 annual deficit, DPW Director Bruce Zimmerman said, which is now being subsidized by the water and sewer operations. Making solid waste self-sufficient, he said, will require a 25% increase that could include bags, tabs, debris, and other fees.

A proposed increase will be presented for city council approval later this year.

Greenhouse

Building a greenhouse is undergoing preliminary review, stressed Mr. Lewand. Heat generated from the digester would be used to maintain a year-around greenhouse in which to grow vegetables. Michigan State University is consulting on the project and is also working on a greenhouse in St. Clair County, and the DPW, he noted, is discussing the sale of the produce with Grand Hotel and Doud's Market. Market owner Andrew Doud is a member of the BPW.

Mr. Lewand said he will be seeking a grant to help fund the project from the Michigan Economic Development Corporation. He estimates the greenhouse would employ about two people year-around and possibly four people in the summer.

In response to questions from East Bluff resident Susan Lenfestey, Mr. Lewand said the board is planning for the possibility that septic tank users will someday tap into the sewer, but has no plan to require that they do. The wastewater treatment plan renovations, he added, do not include expansion of the plant.

“We don't anticipate any growth with this plan on purpose. Our job is to maintain this system and that's what we are doing. We have a limited number of REUs (residential equivalency units) available and we have spaced those out over the next 10 years so growth can be accommodated and managed over the 10-year period.” Proposed Sewer Rate

Increase

Year-around resident annual cost increases, based on 4,000 gallons per month with a 5/8-inch meter. The current annual charge for sewer is $510 a year. (Water charges will not increase and amount to $294 a year.)

2011 increase $35.77 2012 increase $38.17 2013 increase $41.12 2014 increase $43.65

2015 increase $46.75

Seasonal resident annual cost increases, based on 5,000 gallons per month with a 5/8- inch meter. The current annual charge for sewer is $238.55 a year. (Water charges will not increase and amount to $138.74 a year, plus a $100 annual connection fee.)

2011 increase $16.03 2012 increase $17.80 2013 increase $19.16 2014 increase $20.37 2015 increase $21.81