What Do You Feed a Hungry Digester? Assessing the Market for Co-Digestion in Central Maine

If you have excess capacity in an anaerobic digester, don't you want to put it to work? The biggest challenge, though, is finding consistent, reliable high-strength organic waste streams to feed the hungry bugs. Interest in co-digestion in municipal digesters is expanding, but many project promoters are reporting the challenge of finding appropriate supplemental waste streams.The Lewiston-Auburn Water Pollution Control Authority (LAWPCA) has begun construction of a new anaerobic digestion system. With LAWPCA staff and CDM, NEBRA analyzed the potential outside waste streams that may be appropriate for addition to the new digesters. This paper reports on the findings of that study. Phone interviews were conducted with state environmental and planning agency staff, managers of wastewater and biosolids from facilities around southern Maine, and generators of other high-strength organic wastes within 100 miles of the LAWPCA facility.It proved difficult to determine with certainty what outside wastes would most likely be drawn to LAWPCA for disposal. However, it is clear that there is a need in the region for disposal options for fats, oils, and grease (FOG), and LAWPCA would be providing a much-needed service by providing a reliable, cost-effective option for FOG. In addition, generators of some food processing and glycol wastes expressed considerable interest in the possibility of a future disposal option at LAWPCA's facility.In order to attract the desired wastes in consistent volumes, the pricing for disposal has to be competitive. In terms of pricing and availability, the study results indicate that FOG, waste from a food processor, and glycols from a plastics manufacturer are the three most promising outside waste streams for LAWPCA. The estimated gross tipping fees for these wastes range on the order of $50,000 to $150,000 per year based on accepting an average of 3,000 to 6,000 total gallons per day. There are numerous uncertainties that make it a challenge to decision-makers to consider co-digestion. Foremost is that, with all of the current interest in anaerobic digestion and diversion of organic wastes, there is growing competition for these wastes, and generators are playing the market and unwilling to sign long-term contracts, expecting that better pricing is just around the corner. In addition, the struggling economy has reduced activity and waste streams, resulting in competition from landfills and low or no cost options, such as composting and feeding to animals. However, the bright side for LAWPCA is that, in a competitive environment, with the major cost of digester construction paid for, the facility has the opportunity to get ahead of private digestion options and should be able to offer competitive pricing.