Unless the pit is extremely large, however, it won't be enough to harvest. Gas from the pits shown above is simply burned off or vented to the atmosphere. Minnesota researcher are testing a new geotextile cover. The cover is made of a porous plastic fabric that floats on the pit surface. Bubbles beneath the cover are not a problem because the geotextile is porous.
Initial data indicate that geotextile covers significantly reduce gas emission.
An added benefit is that geotextile covers cost much less than the solid plastic covers currently used in Iowa. The larger the storage, the less the cost per square foot, but the greater the total cost. Due to cost considerations and the larger size of anaerobic lagoons, synthetic covers are feasible for pits, but not for lagoons. Because synthetic covers last for many years, their annual costs are comparable to those for biocovers. Overall, synthetic covers are an excellent odor control technology, but they do require some up front investment, and some additional management.