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[Display omitted] • Biogas circulation at 5 L/min could not completely replace mechanical stirring. • Intermittent stripping mode proved applicable for in situ ammonia stripping. • Thermophilic digestion could be promoted to 90% of the methanogenic potential. • Exceeding the loading 4.2 g COD/L/d resulted in failure of the stripping mode. High-solid anaerobic digestion of hydrothermal sewage sludge has been developed. In order to upgrade the process by focusing on ammonia inhibition, a simply-equipped stripping system without additional alkali or heat supply was introduced by in situ biogas self-circulation. As the determined limit of total ammonia nitrogen at 1500 mg/L and 1000 mg/L for the mesophilic (MAD) and thermophilic anaerobic digestion (TAD) respectively and stripping rate at 5 L/min, continuous MAD and TAD was conducted in parallel. The stripping system successfully polished up the ammonia inhibition, and methanogenic capability of the TAD was promoted to approximately 90.0 % of the potential. Intermittent stripping mode proved usable. More frequent stripping was inevitable for the TAD as compared to the MAD. Hydraulic retention time below 20 d resulted in failure of the stripping mode due to rapid ammonia generation. Overall, this technology was practical in upgrading high-solid sludge digestion by effective ammonia control. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hyperthermophilic methanogenesis hardly occurred for de-oiled grease trap waste. • Mesophilic digester could endure the highest loading for single lipid-rich waste. • Limit of long chain fatty acids for hyperthermophilic digestion was 5.6 mmol L−1. • Food waste with composite fractions favored conversion of linoleic and oleic acids. De-oiled grease trap waste (GTW) has been proven appropriate for anaerobic digestion treatment. Continuous hyperthermophilic at 70 ℃, thermophilic and mesophilic digestion were operated in parallel to investigate the distinctive responses to the de-oiled GTW. Mesophilic digestion achieved higher tolerance loading than the others. Biogas production was detected in the recovery period for the inhibited hyperthermophilic digester, and the recovery time lasted approximately 10 days longer than the thermophilic one. The long chain fatty acid (LCFA) concentrations at the starting points of recovery were determined to be 5.6 mmol L−1 and 6.2 mmol L−1 for the hyperthermophilic and thermophilic digestion, respectively. Under the similar lipid loading, food waste with composite fractions was observed favorable for biogas production in the hyperthermophilic digester. Residual lipid concentration remained higher for the hyperthermophilic digestion, about twice more than the others. Furthermore, composite substrate alleviated the inhibition from LCFAs, for the dominant was converted to the ones with shorter chain length. [ABSTRACT FROM AUTHOR]

• Hyperthermophilic digestion of waste activated sludge at 70 °C was characterized. • Methane yield obviously decreased when the hydraulic retention time was below 10 d. • More than 10.2 g VS/L/d resulted in the instability of the methanogenic system. • The kinetic analysis showed that some non-degradable fraction could be converted. • The genera Methanospirillum and Coprothermobacter played significant roles at 70 °C. Anaerobic digestion is promising for waste activated sludge (WAS) degradation. However, conventional processes were generally stuck with limited hydrolysis and poor pathogen destruction. Hyperthermophilic digestion at 70 °C has drawn attention in overcoming those issues at a relatively low energy requirement and operating difficulties. In order to illuminate its operation characteristics, a single-stage hyperthermophilic digester was controlled at 70 °C and operated continuously to degrade WAS. 88.7 mL/g VS added of methane yield could be achieved in the hyperthermophilic system, fourfold higher than that in the mesophilic system. Kinetic analysis revealed that hyperthermophilic digestion was advantageous in converting the non-degradable fraction. Consequently, hydrolysis under the hyperthermophilic condition was able to be significantly improved. Above 10 d was necessary for the hyperthermophilic system to gain such a high methane production. In the case of stability, the organic loading of higher than 10.2 g VS/L/d resulted in increasing limitation from methanogenesis and accumulation of propionic, butyric and valeric acids. In addition to the dominant acetoclastic genus Methanothrix for methane production in the hyperthermophilic system, two hydrogenotrophic methanogens Methanospirillum and Methanothermobacter reached 18.84% and 8.31%, respectively. The genus Coprothermobacter , affiliated with the phylum Firmicutes , made more contribution to protein hydrolysis in the hyperthermophilic digester. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is promising in both food waste reduction and energy upgrading. However, the intermediates in anaerobic digestion of such an oily food waste, long chain fatty acids, not only have low bioavailability but also significantly threaten operation stability. Temperature-phased anaerobic digestion is an emerging technology in recent years, expected to overcome those issues. Given significance of the first stage of the two-stage process, continuous thermophilic digestion of oily food waste was conducted, with mesophilic digestion operated in parallel as control, to determine practical operational parameters from operation performance and stability. The feeding concentration at approximately 4.50 % of volatile solids was identified to be applicative for a relatively stable operation. Due to slow β-oxidation for long chain fatty acids, hydraulic retention time for the first stage needed longer than 10 d to maintain anaerobes' survival so that they were not inhibited. In addition to the risk from inhibition, readily acidified risk still existed, and instant pH control was demonstrated to be efficient in maintaining the habitat of microbial metabolism. Compared with no viable bacteria detected under uncontrolled pH, 36.7 % live cells could still be detected under controlled pH. Overall, thermophilic digestion obviously achieved advantages in higher substance degradation and methane production with lower stability risk. The genera Methanosarcina and Methanothermobacter played a significant role, with the ratio at about 2:1. While bacterial viability was not reduced remarkably in preliminary period of inhibition, long-term operation under high lipid loading resulted in its loss. • A 55 °C–35 °C temperature-phased two-stage system was used to treat oily food waste. • Volatile solid at approximately 4.50% was determined to be appropriate. • Retention time of thermophilic stage needed at least 10 d for stable operation. • pH control was necessary to prevent pH drop and maintain methanogens' survival. • Methanosarcinales dominated acetoclastic methanogens, at above 60.0% in archaea. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A newly acid-resistant strain JR1 was isolated from pharmaceutical wastewater. • A high nitrogen removal could be achieved by JR1 under the acidic condition. • Nitrate began to be utilized as substitute N-source after exhausting of ammonium. • Ammonium was utilized through assimilation along with heterotrophic nitrification. Abstract A new acid-resistant bacterium Acinetobacter sp. JR1 was isolated, and its feasibility in nitrogen removal was investigated under acidic condition. Results show that JR1 indicated excellent ammonium and nitrate removal abilities with no accumulation of intermediates, and the maximum ammonium and nitrate removal efficiencies were 98.5% and 91.1%, respectively. Further experiments demonstrated that JR1 preferred to use ammonium with ammonium and nitrate as the mixed N-sources. For JR1, ammonium was assimilated directly as nutrients into cells and also converted into N 2 through heterotrophic nitrification-aerobic denitrification. Under acidic condition, JR1 performed comparable nitrogen removal abilities to other strains under neutral or weak alkaline environment, and the efficient removal of ammonium occurred at pH 4.5–10, C/N 12–24, 20–40 °C, DO ≥4.72 mg/L, 0–1.5% of salinity, 10 mg/L Zn2+ or 20 mg/L Mn2+. All these make JR1 a promising candidate for treating acidic wastewater containing nitrogen. [ABSTRACT FROM AUTHOR]

• Recuperative thickening (RT) upgraded digestion of hydrothermal high-solid sludge. • Comparative processes with RT were operated at 35 ℃ (MD-R) and 55 ℃ (TD-R). • The MD-R and TD-R increased gas production by 22.8% and 11.0%, respectively. • RT increased hydrolysis rates by 11.1% and 7.4% in the MD-R and TD-R, respectively. • The improved numbers of archaea led to upgraded performances in the RT systems. Recuperative thickening (RT) process was introduced to further upgrade anaerobic digestion of hydrothermal high-solid sludge. Continuous mesophilic (MD-R) and thermophilic (TD-R) digestion with RT (MD-R) were operated synchronously, with corresponding single digestion without RT as controls, namely MD and TD. The MD-R and TD-R increased biogas production rates by 22.8% and 11.0%, and achieved 16.6% and 9.7% higher volatile solids reductions, respectively. The improved performance was partly attributed to increased hydrolysis rate, with 11.2% and 7.4% higher for the MD-R and TD-R than the controls, respectively. The RT increased the numbers of total archaea in the mesophilic and thermophilic systems by 844% and 108%, and the numbers of dominant archaea by 50.4% and 38.1%, respectively, which promoted the degradation of organic matter and the production of biogas. Thus, RT is applicable to further upgrade digesting high-solid sludge. [ABSTRACT FROM AUTHOR]

• Mesophilic (MAD) and thermophilic (TAD) digestion of 10–11% sludge were studied. • 160 °C for 210 min was the optimal hydrothermal pretreatment (HTP) condition. • TAD exhibited higher methane production than MAD under stable conditions. • 2800 mg/L of NH 4 +-N resulted in an inhibition of methane production in TAD. • The energy balance of MAD with HTP was the highest, 5.25 kJ/g VS. Hydrothermal pretreatment (HTP) conditions were optimized for continuous mesophilic (MAD) and thermophilic (TAD) anaerobic digestion of high-solid sludge (10–11% total solids). COD solubilization increased with prolonged HTP durations, and became not significant after 210 min. According to the methane production rate and energy consumption, the optimal HTP temperature was determined at 160 °C. Regarding continuous operation without HTP, TAD achieved higher methane yield and volatile solids (VS) reduction, at 0.12 L/g VS added and 23.9%, respectively. After HTP, methane yield and VS reduction in MAD and TAD were increased by 400% and 191% (MAD), 67% and 72% (TAD), respectively. TAD was limited due to the inhibition from about 2800 mg/L of NH 4 +-N concentration. The methanogenic activity of MAD was enhanced, whereas TAD displayed a reduced value owing to ammonia inhibition. Ultimately, MAD with HTP and TAD without HTP achieved the higher energy balance, 5.25 and 3.27 kJ/g VS, respectively. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is a promising waste-to-energy alternative technology. However, the efficiency upgrading for conventional mesophilic digestion of organic solid waste is always indispensable. Employing hyperthermophilic or thermophilic microbial community is one of the viable upgrading alternatives. Given the unavailability of the superior microbial communities, mesophilic digested sludge was used as inoculum, and instantly controlled at 70 °C and 55 °C for acclimation of hyperthermophilic and thermophilic inocula, respectively. Waste activated sludge was continuously and synchronously fed into two digesters. After one round, thermophilic digester achieved stable biogas production rate at 0.22 L L−1 d−1, with a methane proportion over 60%, whereas fluctuation was observed in the hyperthermophilic digester, and approximately triple time was needed to reach a relatively stable biogas production rate 0.12 L L−1 d−1. Nevertheless, higher hydrolysis ratio 24.4% was observed in the hyperthermophilic digester despite the lower biogas production. Therefore, methanogenesis step limited the whole anaerobic process for the hyperthermophilic digestion, and digestion at 70 °C was appropriate as a pre-fermentation stage to enhanced hydrolysis. The genus Methanothrix proportion in the thermophilic digester gradually decreased, while another acetoclastic genus Methanosarcina ultimately was acclimated to the dominant methanogen. In addition to Methanothrix , hydrogenotrophic archaea became competitive in the hyperthermophilic digester, with Methanothermobacter dominant at 22.6%. The genus Psychrobacter , affiliated to the phylum Proteobacteria could survive better than the others at 70 °C, with a final proportion of 62.5%. • Hyperthermophilic microbial community was established from mesophilic sludge. • The differences between digestion at 70 °C and 55 °C were profoundly discussed. • Hydrogenotrophic archaea Methanothermobacter was another dominant genus at 70 °C. • Higher hydrolysis ratio 24.4% was achieved in the hyperthermophilic digester. • Methanogenesis was the rate limiting step for hyperthermophilic digestion. [ABSTRACT FROM AUTHOR]