Certain basic materials are required for the purposes of filtration, especially biofiltration. In a filter reactor, granular material is used to achieve both filtration and biochemical transformation of contaminants.
Materials with rough surfaces have been found to produce the best results, as bacteria can colonise such surfaces more easily. A form of bacterial biofilm develops on the particles. It is these microorganisms that are responsible for the breakdown of the contaminants in polluted water.
Various natural materials of volcanic origin can be used as filter materials, such as lava stone, pumice, zeolite and basalt. Potential applications are drinking water and waste water filtration, plant-based clarification systems, basin reactors, clarification beds, ponds and aquaria, to name but a few. In each case, the basic principles are the same.