Aluminum chloride enhances the production of short-chain fatty acids from waste activated sludge: Insights to performance, mechanism, and implications

Waste activated sludge (WAS), the major by-products during wastewater treatment, is hugely produced, which poses great environment and operation pressures. This work investigated feasibility, mechanism, and implications of aluminum chloride for carbon recovery enhancement from WAS. Results showed that aluminum chloride enhanced short-chain fatty acids (SCFAs) production potential, and the enhancement potentials were dosage dependent. The optimal dosage was 10 mg Al/g total suspended solids (TSS), with the maximum SCFAs production potential of 140 mg chemical oxygen demand/g volatile suspended solids, which was 52.2 % higher compared to that of control. Meanwhile, the compositions of SCFAs were regulated, suggesting that the recovered SCFAs were potential carbon source. Mechanism analysis showed that aluminum chloride increased the release of polysaccharides and proteins by 23.6 % and 71.7 %, respectively, compared to that in control, as well as the removal of extracellular polymeric substances to 27.5 % and the contribution of intracellular release to 38.0 %. This situation facilitated the solubilization of WAS and improved the biochemical degradability of organic matters. In addition, aluminum chloride promoted hydrolysis and acidification stages through affecting the activities of hydrolase, enriching acid-producing microorganisms, and inhibiting the activities of methanogens. This work provided some novel solutions for sludge treatment and carbon recovery, driving wastewater treatment plants to achieve carbon-neutral operation.