Thiosulfate/FeCl3 pre-treatment enhances short-chain fatty acid production and mitigates H2S generation during anaerobic fermentation of waste activated sludge: Performance, microbial community and ecological analyses

Revealing the effect of Al2O3 on sulfur transformation in anaerobic sludge process

Al2O3, one multifunctional adsorbent and dehydrator, was widely recognized as a practical and environmentally friendly additive that enhances fermentation efficiency and facilitates the recovery of resources from waste-activated sludge (WAS). However, its potential harmful effects on WAS fermentation, such as the generation of hydrogen sulfide (H2S), have been previously overlooked. This study found that with the increase of Al2O3 dosage from 0 to 60 mg/g VSS, the maximum production of H2S decreased from 371.60 ± 3.72 × 10-4 to 303.36 ± 3.03 × 10-4 mg/g VSS. The study on the transformation of sulfur-containing compounds has identified that the primary cause for lowering the formation of hydrogen sulfide (H2S) is the inhibitory effect of aluminium oxide (Al2O3) on sulfate reduction. The mechanism analysis discovered that Al2O3 initially stimulated the functional groups and hydrogen bonding networks present in sludge EPS. This resulted in a 2.04 % rise in the content of C-C groups, a 7.78 % increase in the content of C-O-C groups, and a 4.24 % increase in the content of β-turn and α-Helix structures. This resulted in the fracturing of sludge EPS and the release of soluble metal ions such as aluminium, magnesium, and iron. The liberated metal ions facilitated the conversion of H2S gas and dissolved sulfide into metal sulfide, hence contributing significantly to the reduction of H2S gas emissions. Microbial community research revealed that the inclusion of Al2O3 enhanced the performance of methanogens (e.g., Methanothrix), but inhibited sulfate reducing bacteria (e.g., unclassified_c__Deltaproteobacteria). Additional examination of functional genes demonstrated that Al2O3 decreases the amount of functional genes involved in the hydrolysis of organic sulfur (such as MetQ, pepD, CDO1, yhdR, etc.). and sulfate reduction processes (sat, cysC, aprAB, dsrAB, etc.). These findings offer novel perspectives on the treatment of sludge using Al2O3 and could have substantial consequences for sludge treatment.

A novel strategy to promote sludge solubilization and short-chain fatty acid production by coupling thermal hydrolysis and sodium thiosulfate pretreatment

Thermal hydrolysis (TH) technology is promising for sludge pretreatment, but the high cost and the generation of refractory substances limit its application. In this study, sodium thiosulfate (STS) was innovatively combined with TH pretreatment to improve the anaerobic fermentation efficiency of sludge. TH-STS pretreatment (140 °C, 0.132 g/g TSS) increased sludge solubility by 33.4 % and increased short-chain fatty acid (SCFA) production to 1.86 times that of the control group. TH effectively stripped the extracellular polymeric substances, and STS subsequently lysed the cells through its reducing power. TH-STS pretreatment promoted SCFA accumulation by increasing the activity of key enzymes and enriching hydrolyzing and acidifying bacteria. In addition, TH-STS pretreatment increased the activity of the electron transport system, which positively promoted the biotransformation of SCFAs. This study reveals that STS and TH pretreatment have a synergistic effect, providing an effective method for improving sludge pretreatment and resource recycling.