Alternative filter materials to natural sand and gravel in soil-based wastewater treatment systems

Journal article, 2026

Natural sand and gravel are widely used as filter media in soil treatment systems for decentralized wastewater treatment, but their extraction contributes to resource conflicts and environmental pressure. This study evaluated seven alternative filter materials: crushed rock, crushed concrete, washed excavated material, glacial till, bark, shredded tires, and biochar. A multi-criteria analysis was applied to assess technical performance, environmental sustainability, economic feasibility, and social acceptability. Bark showed strong environmental and social performance, while shredded tires and glacial till scored well in technical and economic criteria. Crushed concrete and washed excavated material performed similarly to natural gravel, whereas biochar scored lower due to high cost and uncertainty regarding long-term hydraulic and structural behavior. Across materials, trade-offs and data gaps were evident, particularly regarding long-term pollutant removal, leaching risks, and consistency of material quality. No single alternative outperformed natural gravel under all conditions. However, several materials demonstrated clear potential, provided that quality control measures are applied and field-scale validation is conducted. The applied multi-criteria framework provides a transparent basis for selecting sustainable filter materials and supports efforts to reduce dependence on natural gravel in decentralized wastewater treatment systems under context-specific conditions.