In the Siemens summer and winter pilot studies, the IPS composting system served a dual purpose by biodrying materials for fertilizer or fuel while using less energy compared to thermal drying. The system consistently dried to 65 percent solids with an in-feed mixture of at least 40 percent solids, comprised of dewatered cake (of at least 20 percent solids) and recycled dried product discharged from the IPS system (of at least 60 percent).
Photo courtesy of Siemens AG

Industry's need for a versatile biosolids end-product that could be produced using less energy pushed Munich-based Siemens Water Technologies to do a little exploring. The company examined a new application for the company's existing integrated power systems (IPS) composting technology by focusing a pilot study on mechanically enhanced biodrying (MEB).

The study illustrated how the current IPS system serves a dual purpose by biodrying materials for fertilizer or fuel while using minimal energy compared to conventional drying methods. The results showed that an automated, agitated bin-composting technology could achieve 65 percent solids concentration (35 percent moisture) in biosolids by using only the finished dried product as the amendment.

The MEB process uses the biosolids’ own biological characteristics to heat the material and, in doing so, evaporates some of the moisture. Aeration and agitation from the IPS equipment further enhance the biological drying process. The IPS biodrying process is more efficient than thermal drying, and the end-product can be used as fertilizer or feedstock for incineration, according to Siemens.

Creating a biosolids fuel product with an energy-conservative process makes MEB suitable for conversion technologies. The study also found that applying similar MEB principles to biosolids composting addresses the challenge confronting plants when wood waste and other carbon-rich amendments are in short supply. Further research is looking at using the process before gasification.