Mechanisms of calcium ion inhibiting alkaline fermentation of waste activated sludge for short-chain fatty acids production

Alkaline fermentation is an effective way for short-chain fatty acids recovery from waste activated sludge. However, there is always a high content of calcium ions in waste activated sludge, which may inhibit alkaline fermentation resulting in a low short-chain fatty acids production. The inhibition effect and mechanisms of calcium ions on short-chain fatty acids production from waste activated sludge was investigated and studied in this work. The results showed that when the calcium ions concentration increased from 0 to 5000 mg/L, the short-chain fatty acids production decreased from 307.8 +/- 0.7 to 226.8 +/- 1.1 mg chemical oxygen demandig volatile suspended solid. Mechanism study revealed that about 2-fold extracellular polymeric substances were secreted with 5000 mg/L calcium ions addition than that of calcium ions absence to resist the toxic effect of calcium ions, thus inhibiting waste activated sludge disintegration, and less organic substrate were released for the short-chain fatty acids production. Furthermore, flocculation of calcium ions and short-chain fatty acids reduced the short-chain fatty acids concentration in fermentation liquid. (C) 2022 The Author(s). Published by Elsevier B.V.

Automated summary

This study investigated the inhibition effect and mechanisms of calcium ions on short-chain fatty acids production from waste activated sludge. The results showed that a high concentration of calcium ions reduced the production of short-chain fatty acids, possibly by inhibiting sludge disintegration and reducing the release of organic substrates.