Discussing porosity loss of Fe0 packed water filters at ground level

• Granular Fe0-based filters for water treatment are difficult to design.
• Permeability loss in Fe0 filters corresponds to physical pore obstruction.
• Factors determining the permeability of Fe0 filters include particle size (R0).
• Porosity loss is discussed as function of R0 depletion for the first time.
• A universal ‘radius depletion equation’ is established for modeling porosity loss.

The use of granular metallic iron (Fe0) as filter material is gaining acceptance in the field of water treatment. Few works have been directed at developing design guidance for efficient Fe0 filters. This note consolidates earlier works and provides the scientific basis for the design and evaluation of Fe0 filters for water treatment at any scale. The approach assumes uniform corrosion of individual Fe0 particles and utilizes the radius loss (X = R0 − R) to asses the extent of porosity loss in the whole system. Results corroborate that, for R0 ⩽ 1.0 mm, sustainable filters must content less than 53% Fe0 (v/v). A universal equation of Fe0 filters is provided given X as a function of the initial radius R0, the initial volume of Fe0, the initial porosity of the filter and the coefficient of volumetric expansion (O2 availability). This equation should be routinely incorporated in simulations for modeling the hydraulic conductivity of Fe0 filters. The model improves the discussion of published data on porosity loss.