SOUTH BEND -- The city could save more than $1.4 million on a package of upgrades to its sewage treatment plant after bids from several contractors undershot the project's original $7 million estimate.
The low bidder, Hudsonville, Mich.-based Grand River Construction, submitted a total estimate of just less than $5.6 million for an overhaul of one of the treatment plant's two primary digesters -- huge vats that utilize heat and bacteria to break down and sanitize solid waste.
"The engineer's estimate was $7 million, so I was pretty happy with those numbers," said Gary Gilot, president of the city Board of Public Works, which opened the bids Tuesday morning.
The two other bids also came under the city's estimate. Westfield-based Thieneman Construction submitted a total bid of about $6.4 million, while Miller Davis Construction, of Kalamazoo, Mich., bid a total of just under $6.7 million.
Al Greek, the city's director of environmental services, said the upgrades would include the replacement of all the digesters' major components, such as pipes, valves, pumps, controls and electrical systems.
As part of the project, the city also will install a new "gas-scrubbing" system designed to produce a greater amount of usable methane gas -- a natural byproduct of the process -- Gilot said.
As the digesters break down solid waste, they produce water and methane. The city uses about 50 percent of the methane to power some of its boilers and burns the rest off because it contains impurities that make it unsuitable as a power source, Greek said.
The gas-scrubbing system will give the city a higher percentage of usable gas, Greek said. In the future, the city may take some of the gas produced by the digesters and compress it so it can be used to fuel methane-burning vehicles in the city's fleet, he said.
Although not directly related, Greek said the upgrades would also allow the treatment plant to handle an increased flow of wastewater as the city embarks on a $509.5 million plan to reduce raw sewage overflows into the St. Joseph River.
In December 2011, the city and U.S. Environmental Protection Agency entered into a consent decree that requires the city to do about $509.5 million of work over 20 years to reduce annual overflows from the city's combined sanitary and stormwater sewers during periods of heavy rain.
In recent years, 700 million to 800 million gallons of raw sewage has spilled from city sewers into the river annually, though not all of that includes solid waste, Greek said. As the city reduces overflows, more of that wastewater will flow into the treatment plant.
"The facility here has got to be ready to take that increased flow," he said.
The city is still in the very early stages of the overall $509.5 million plan.
Greek said the city will likely select the winning bidder for the digester upgrades within 30 days. Construction could start by the end of the year and will last about two years, he said.
Although all three contractors submitted bids under the $7 million estimate, some of the savings could go toward unforeseen extra costs, Greek said.
"This makes this project a little easier because it makes room for change orders," he said.