Agenda - Council - 05/26/1981 - Laserfiche WebLink

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METHANE FROM LANDFILLS -2- April 1, 1981" Since the Palos Verdes landfill methane production project became operational, several other landfills have been tapped for the same purpose. For example, Reserve Synthetic Fuels (which is not the only corporation involved in methane from landfill programs) now has two high-Btu gas plants operating in southern California and one in Chicago. Another is under construction in New York and will begin production in 1982. In addi- tion, Reserve has two medium-Btu plants (to produce industrial-quality gas) under construction, both of which should become operational during 1981. With this experi- ence, Reserve feels that the technology is well established for collection and purifi- cation of methane from deep landfills.3 Shallow landfills (those 40 to 50 feet deep, or less), which are typical in the Midwest, are another matter. In a deep landfill (100 or more feet deep) there is relatively little infiltration of air into the depths of the landfill, and thus conditions are ideal for anaerobic (methane-producing) bacteria. As methane is withdrawn from a shallow landfill, however, there is a tendency for air to seep in to replace the meth- ane, and this kills off the methane-producing bacteria. This problem can be alleviated to some extent by keeping the rate of pumping low, but that also reduces the economic ~zeturn on the capital investment in the collection and purification systems.4 For this reason, no landfills in the Midwest have been tapped for methane, with the xception of a deep landfill near Chicago. However, Anoka County is investigating he possibility of deriving methane from their landfill. At the present ~ime, they ave not obtained federal funds for a feasibility study, but are considermng going ahead with such a study using their own funds.5 In addition to depth, the total volume of a landfill is an important factor in methane production. So far, methane has been collected for energy purposes only from large landfills. For example, the Mountain View landfill in California6 accepts slightly 'more wastes each year than the largest landfill in Minnesota;7 while it was open, the Palos Verdes landfill received more than twice that volume each year.8 Another unin- vestigated factor in methane production is the local climate. Minnesota is signifi- cantly colder than California (where most methane collection has been done) and this is likely to reduce the production of methane, especially during the winter.9 An alternative method of producing methane from shallow landfills has been proposed researchers at the Institute of Gas Technology (IGT). Their suggestion is to collect organic acids from the landfill and pipe them to processing tanks (called digesters) which ensure anaerobic (oxygen-free) conditions. There methane is produced, collected, 'and purified with the residue being fed back to the landfill for further decomposition by the acid-producing bacteria. Although this procedure is under study in the labora- tory, funding has not been available to set up a pilot or full-scale project to test the process in the field,l0 Another alternative is to skip a landfill entirely'and put solid wastes directly into digesters. The advantage of this approach is that conditions within the digester can be controlled much more p~ecisely than those in a landfill, allowing maxlmummethane production. However, they are much more capital intensive than the approach suggested by IGT, and it is likely that some methane production would be sacrificed to improve the economics of the process by moving material from the digester before decomposition is completed. The undigested portion would still have to be landfilled or incinerated, which increases the total cost of this approach. Il,12 Resource Recovery and Methane Production With the rising cost of raw materials and increased difficulties in establishing new landfill sites acceptable to the public, interest has grown in the recovery of a