Abstract
A high solid digester with dewatered sludge was operated for 110 days to ascertain the interactions between bacterial and archaeal communities under ammonium stress, as well as the corresponding changes in bio-degradation mechanisms. The volatile solids reduction (95% confidence intervals in mean) changed from 31.6 ± 0.9% in the stable period (day 40–55) to 21.3 ± 1.5% in the last period (day 71–110) when ammonium concentration was elevated to be within 5,000–6,000 mgN/L. Biogas yield dropped accordingly from 11.9 ± 0.3 to 10.4 ± 0.2 L/d and carbon dioxide increased simultaneously from 35.2% to 44.8%. Anaerobranca better adapted to the ammonium stress, while the initially dominant protein-degrading microbes-Tepidimicrobium and Proteiniborus were suppressed, probably responsible for the increase of protein content in digestate. Meanwhile, Methanosarcina, as the dominant Archaea, was resistant to ammonium stress with the constant relative abundance of more than 92% during the whole operation. Nonmetric Multidimensional Scaling (NMDS) analysis was thus conducted which indicated that the gradually increased TAN dictated the bacterial clusters. The dominant Methanosarcina and the increased carbon dioxide content under ammonium stress suggested that, rather than the commonly acknowledged syntrophic acetate oxidation (SAO) with hydrogenotrophic methanogenesis, only SAO pathway was enhanced during the initial ‘ammonium inhibition’.
Highlights
State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, PR China. *These authors contributed to this work
Niu et al.[24] reported that carbohydrate degradation efficiency was 60% at 6,000 mgN/L TAN concentration, and stable protein conversion could be achieved only when TAN was lower than 3,000 mgN/L
The protein removal efficiency decreased from 40% at TAN of 1,500 mgN/L to only 10% at TAN of 6,000 mgN/L, while no obvious changes in carbohydrates were observed, confirming that protein degradation is more vulnerable to ammonium loading than carbohydrate degradation
Summary
State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, PR China. *These authors contributed to this work. When high solid anaerobic digestion systems are applied to treat protein-rich sewage sludge, ammonium concentration usually exceeds the tolerance of microbes degrading organic substances. The objective of the current study was to investigate the effects of elevated ammonium stress on both evolution of individual organic composition and relevant microbial adaptation in a long-term high solid anaerobic digester with dewatered sludge. The changes of organic matters such as proteins, carbohydrates, and lipids in anaerobic digestion were monitored. The dynamics of both bacterial and archaeal communities was analyzed by pyrosequencing and presented with changes in relative abundance. Combined with the analysis on the changes of Methanosarcina density before and after ammonium addition by real-time polymerase chain reaction, the understanding on the instinctual interactions responding to ammonium stress was subsequently obtained
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