The study illustrated how the IPS system serves a dual purpose by biodrying materials for fertilizer or fuel while using minimal energy expenditure, compared to conventional drying methods. It was determined 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.
An IPS composting system agitator similar to the technology used in the MEB pilot studies, where 65 percent solids concentration (35 percent moisture) was achieved in biosolids, using only the finished dried product as the amendment. Picture: Siemens AG
In the pilot study, the IPS Composting System was found to consistently dry 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). Overall, the solids concentration increased an average of approximately one percent per day and as much as two percent per day in the agitated bin system when minimum in-feed conditions were met. Summer and winter studies focused on such variables as ambient air temperature, feedstock properties, turning frequency, bin retention time, and process aeration cycles.
The MEB process uses the biosolids’ own biological characteristics to heat the material and, in doing so, to evaporate some of the moisture. Aeration and agitation from the IPS equipment further enhance the biological process drying. The IPS biodrying process is more cost effective and energy efficient than thermal drying, and the resultant end-product can be used as fertilizer or feedstock for incineration. Creating a biosolids fuel product with an energy-conservative process makes MEB an ideal companion for conversion technologies. It was 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 also possibly using the process before gasification.
A versatile system like the MEB that is capable of both composting and biodrying ensures WWTPs of a long-term flexible solution. On the one hand, some EU countries such as Austria, Denmark, Germany, the Netherlands, and Slovenia have stricter country-specific regulations regarding the agricultural use of biosolids by significantly limiting the maximum annual application of heavy metals. Where agricultural utilization is restricted, incineration is often selected as the sludge or biosolids management option. Therefore, biodrying or MEB would be an appropriate step before incineration. On the other hand, roughly 38 percent of EU countries land-apply treated biosolids, with France, Ireland, Spain, and the UK topping that list. Many of these countries have found composting to be a more socially acceptable, energy-efficient, and environmentally-friendly alternative to landfilling or incineration.
Besides municipal WWTPs, the IPS system is also applicable to other industries: the UK Department of Environment, Food and Rural Affairs (DEFRA) recently approved the IPS system, to be considered a "closed reactor" under Regulation (EC) 1774/2002 to compost catering wastes. The United Kingdom has composting guidelines that are more stringent than most of the other EU countries because of concerns over swine vesicular disease, foot-and-mouth disease, and other animal-related infections.Contact USA:
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Stefanie Schiller | Siemens Industry
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