ROYAL OAK, Mich. (AP) -- The Detroit Zoo is planning to turn abundant piles of animal manure into energy. The zoo in the Detroit suburb of Royal Oak says Monday that construction on the anaerobic biodigester begins this spring and will be completed this year. The biodigester will turn about 400 tons of manure a year as well as other organic waste into methane-rich gas. This gas will be used to help power the 18,000-square-foot Ruth Roby Glancy Animal Health Complex, saving $70,000 to $80,000 in annual energy costs. The system also will convert manure into compost that will be used to fertilize animal habitats, gardens and public spaces. As part of the effort, the Michigan Economic Development Corp. and the Detroit Zoological Society are conducting a crowdfunding campaign.