Rohasche

Rohasche is a term used in German-speaking contexts to describe the coarse ash fraction produced by combustion processes, typically the bottom ash that collects at the bottom of incineration chambers in waste-to-energy plants and biomass boilers. It is distinguished from finer fly ash, which is carried with flue gases and captured by filtration systems. Rohasche may be referred to as raw or untreated ash before any stabilization, refinement, or treatment.

The material consists mainly of inorganic minerals derived from the burned feedstock, including oxides of silicon, calcium, aluminum, potassium, and iron, along with trace amounts of metals and unburned carbon. Its composition varies with the type of fuel and combustion conditions. Rohasche is usually dense and coarse and can contain relatively high pH due to calcium and other alkaline components.

Management and use of Rohasche involve collection, characterization, and, in many jurisdictions, stabilization or treatment to control leaching of salts and contaminants. Possible pathways include metal recovery (both ferrous and non-ferrous), granulation or conditioning for use as a construction material, road base, or fill material, and, when hazardous constituents are present, disposal in permitted facilities. The suitability for beneficial use depends on regulatory standards, leaching tests, and the specific composition of the ash.

Environmental considerations center on the potential for leachates and the concentration of heavy metals and soluble salts. Regulatory regimes in many regions require testing and sometimes treatment before any reuse or disposal. See also: fly ash, bottom ash, incineration ash, waste-to-energy.