Grand Rapids’ wastewater division is preparing to build a biodigester at its water resource recovery facility.The city’s environmental services manager, Mike Lunn, tells MLive the division has known for a while that it would need to adjust its operations to treat a growing stream of highly concentrated food waste from Founders Brewing Company, Coca-Cola, Amway and SET Environmental. The biodigester, including a new pipe and sludge treatment system, is expected to cost nearly $30 million.Lunn said the city decided building a biodigester was the best option, rather than make a $90 million expansion to the plant or require businesses to pre-treat their waste.