Exploring the potential of sewage sludge ash for CO2 sequestration and resource recovery

Abstract

The incineration of sewage sludge generates ash (SSA), which shows an increasing interest due to its potential for phosphorus recovery. The most promising application of SSA is as a fertilizer. However, direct use in agriculture faces significant challenges due to low nutrient bioavailability. Moreover, SSA has the potential for CO₂ capture through carbonation owing to their calcium content, which eventually increases the potential for P extraction due to the pH lowering. This study explores an experimental carbonation process applied to SSA, marking the first application of this technique to such waste. The carbonation was conducted in a high-pressure reactor in a fluid phase (slurry) to promote mineralization and the formation of carbonates. The better results were obtained for the SSA sample containing the higher calcite amount (about 28 %) with the capability to sequestrate about 20 kg of CO₂ for 1 ton of dry matter. Moreover, the results indicated that carbonation did not significantly improve the phosphorus leaching potential of the SSA compared to the untreated samples when acid extraction was performed. However, a strict correlation between the amorphous content and the P leachability was found for the first time, with a 0.7 % extraction efficiency for the sample with 15.2 % amorphous and 52.1 % extraction efficiency for the sample with 42 % amorphous. The results are promising for further research on optimizing the carbonation processes and exploring additional treatments to improve SSA's agricultural viability and CO₂ capture.