Demetalization of sewage sludges through physico-chemical processes
The agronomic use of sewage sludge has as main constrain the presence of high content of heavy metals. The proposed process optimizes their dissolution by a suitable combination of acid and complexing agents as extractant and thereafter the recovery of metal-enriched fractions using membrane separation and cation exchange techniques
Different processes have been effectively used for the demetallization of sewage sludge: chemical extraction, bioleaching, electrokinetic processes and supercritical fluid extraction. Of all these, is the chemical extraction which achieved the most promising results of implementation, although due to the high variability in the origin and state of sludges, the high treatment volume and the associated cost, is essential to achieve the maximum metal recovery with the minimum operating cost, which is achieved by optimizing the extractive agent and an appropriate combination of membrane separation processes and cation exchange resins.
The experiments carried out by the research group UBUCOMP, show that it is possible to achieve a significant decrease in the metal content of sewage sludge, whether from primary, secondary or after anaerobic digestion processes. The scaled to pilot plant is feasible from an operational point of view and costly efficient, constituting one interesting option for obtaining a final demetallised sludge with a potential use as organic fertilizer.
The reduction in the metal load of sewage sludges in an in situ process to be introduced in the treatment plant, is a feasible option in terms of technical and economic balances and can be added to the actual management scheme of sewage sludge. The improved process allows the recovery of metal fractions and a final product with a high organic matter and nutrient contents, that can constitute the basis for the formulation of an organic fertilizer.
This technique would be of interest to stakeholders involved in sewage sludge management, sewage treatment plants, landfills or industrial plants that generate effluents with high organic and metallic charge.
COMPOSTING RESEARCH GROUP
Jose Manuel López López
+34 947 25 8895