Agitated Bed Composting: Past, Present, Future

The agitated bed composting technology has been a success story atypical of other mechanical, in-vessel technologies developed for the composting of biosolids. Over 70% of all such facilities ever constructed continue to operate, some for as long as 17 years. The greatest number of facilities constructed occurred during the decade between 1990 and 2000. While growth in the number of new facilities constructed has not been maintained, the quantity of material composted continued to increase through 2004 as the capacity of individual facilities increased.The major advantages of the in-vessel agitated bed technology are considered to be:mechanical simplicity.process and mechanical accessibility,operational and process control flexibility,wide choice in amendments for structure and biodegradable carbon,adaptability of the system by engineers and operators to take advantage of local opportunities and limitations,The development of new facilities has been limited due to competing, low cost options such as land application and landfilling of Class B biosolids, and open-air windrow composting on a compacted earth surface. The purpose of this paper is to review the history of agitated bed technologies, discuss the process success, operational survival, and innovations of these technologies, and to suggest opportunities as well as limitations for growth of these technologies.