Effects of various pretreatments on biological sulfate reduction with waste activated sludge as electron donor and waste activated sludge diminution under biosulfidogenic condition

Sulfidogenic anaerobic digestion of sulfate-laden waste activated sludge: Evaluation on reactor performance and dynamics of microbial community

This study investigated the impact of sludge retention times (SRTs: 40, 20, 10 and 5 days) on performance of the sulfidogenic anaerobic digestion (SAD) reactor treating sulfate-laden waste activated sludge and dynamics of sulfate reducing bacteria (SRB). The findings showed that sulfide production, volatile sludge removal efficiency, ammonia release and methane yield decreased by 33.7%, 66.4%, 21.3% and 68.7%, respectively when SRT was shortened from 40 to 5 d. Significant enrichment of hydrolyzers/fermenters (genera Mesotoga and Sulfurovum) was observed at longer SRT (40 d), but shorter SRT (5 d) favors enrichment of diverse SRB (genera Desulfomicrobium and Desulfovibrio). PICRUSt data revealed bacterial communities possessed diverse predicted functions including sulfur metabolism enzymes (e.g. sulfate adenylyltransferase), and their abundance was higher at shorter SRT. Statistical analysis (PCA) confirmed positive relationships between SRB and SAD performance. The findings of this research could be useful for design and optimization of sulfidogenic-based anaerobic digestion process.

Enhanced reduction of waste activated sludge at a low temperature by locally isolated strains Pseudomonas sp. VNT and Aeromonas sp. VNT

Appropriate control of waste activated sludge (WAS) is required to solve the annual increment of WAS volume. The low bacterial activity at low temperatures poses a difficulty in reducing or utilizing WAS in cold weather regions and/or during the winter season. This study reveals a practical method to enhance sludge reduction at a low temperature using isolated strains of Pseudomonas and Aeromonas species. The effect of inoculating each strain into WAS was examined at different temperatures (4°C, 10°C, 12°C, 15°C, 20°C, and 30°C) and under an aerobic condition. Sludge reduction showed 2- to 8-fold improvement at the temperature range from 4°C to 15°C. Both strains are psychrophilic and can produce protease and lipase for sludge degradation even at low temperatures. Thus, biological WAS treatment at a psychrophilic temperature can be enhanced by inoculating these promising strains.