Upgrading the anaerobic membrane bioreactor treatment of chicken manure by introducing in-situ ammonia stripping and hyper-thermophilic pretreatment.

The slow hydrolysis rate and ammonia inhibition effects significantly limit the performance of anaerobic digestion (AD) of nitrogen rich wastes. An innovative two-stage AD was therefore investigated for chicken manure by combining hyper-thermophilic (70 °C) pretreatment and a anaerobic membrane bioreactor (AnMBR). An in-situ stripping unit was assembled into the AnMBR to remove the ammonium-N, thus alleviating the inhibition effects. Through the 120-day experiment, the hydraulic retention time was optimized at 15 days for AnMBR with a constant retention 4 days for pretreatment. The hydrolysis efficiency and methane yield reached 72.4% and 352 mL-CH4/g-VSin respectively. About 3000 mg/L ammonium-N was removed through stripping, attributing to methane yield increased by 139 mL-CH4/g-VSin and volatile fatty acids decreased by 2683 mg/L compared to the control. No significant fouling was observed for the membrane. Conclusively, the combined two-stage AD process may offer an alternative approach for the treatment of nitrogen rich organic waste.

Enhancing hyper-thermophilic hydrolysis pre-treatment of chicken manure for biogas production by in-situ gas phase ammonia stripping.

Hydrolysis is normally the rate limiting step for anaerobic digestion (AD). In this study, hyper-thermophilic (70 °C) pre-treatment of chicken manure under HRTs of 10, 5, 3, 2 and 1 d(s) was investigated to enhance the hydrolysis efficiency for biogas production. In-situ phase gas stripping was integrated into the pre-treatment reactor to remove ammonia-N and to enhance the hydrolysis performance. The results showed that in-situ gas stripping removed 18%-31% of ammonia-N and improved hydrolysis by 2.6%-31.1%. The methane yield of pre-hydrolyzed chicken manure reached 518 mL g-VS-1 under optimal HRT 3 days, which was 54.6% higher than that obtained from the control reactor. However, shortening HRTs below 3 days resulted in a significant reduction in hydrolysis efficiency. The percent of hydrolysis and acidogenesis bacteria reduced to 40.6% at HRT 1 d. 16sRNA results indicated existence of methanogens in pre-hydrolysis reactor. Further optimizing of ammonia stripping was thus needed for hydrolysis pre-treatment.

An explanation of the methanogenic pathway for methane production in anaerobic digestion of nitrogen-rich materials under mesophilic and thermophilic conditions.

The impact of temperature on the anaerobic digestion of chicken manure was investigated by studying the process performance and pathway for continuously-fed digesters under mesophilic and thermophilic conditions. The mesophilic digester obtained a 15% higher methane yield compared with the thermophilic digester. Mesophilic and thermophilic digester had free ammonia of 31 and 145 mg/L, respectively. The stable carbon isotope analysis indicated that 41% and 50% of acetate was converted to methane through the syntrophic acetate oxidation and hydrogenotrophic methanogenesis (SAO-HM) pathway under mesophilic and thermophilic conditions, respectively. The genus Pseudomonas represented 10% and 16% under mesophilic and thermophilic conditions, respectively. A high abundance of the methanogens genus Methanoculleus (94% of total methanogens) in mesophilic and the genus Methanothermobacter (96%) in thermophilic digesters indicated they were the main hydrogenotrophic partners in SAO. The present study therefore illustrated that methanogenic pathway shifting, induced by free ammonia, closely correlated to the process performance.

Rhizobium tibeticum sp. nov., a symbiotic bacterium isolated from Trigonella archiducis-nicolai (Sirj.) Vassilcz.

Isolated from root nodules of Trigonella archiducis-nicolai (Sirj.) Vassilcz. grown in Tibet, China, cells of the bacterial strains CCBAU 85039(T) and CCBAU 85027 were Gram-negative, aerobic, motile, non-spore-forming rods that formed colonies that were semi-translucent and opalescent on yeast extract-mannitol agar. In numerical taxonomy, SDS-PAGE analysis of whole-cell proteins and DNA-DNA hybridization, the two strains were very similar and were different from reference strains of defined Rhizobium species. In the phylogeny based on 16S rRNA gene sequences, they were most similar to Rhizobium etli CFN 42(T) (98.2 % similarity) and R. leguminosarum USDA 2370(T) (97.6 %). Sequence analyses of the housekeeping genes recA, atpD and glnII and the 16S-23S rRNA intergenic spacer, phenotypic characteristics and cellular fatty acid profiles strongly suggested that these two strains represented a novel species within Rhizobium. Cross-nodulation tests and sequencing of nifH and nodA genes showed that these two strains were symbiotic bacteria that nodulated Trigonella archiducis-nicolai, Medicago lupulina, Medicago sativa, Melilotus officinalis, Phaseolus vulgaris and Trigonella foenum-graecum. Based on the results, the novel species Rhizobium tibeticum sp. nov. is described to accommodate the two strains. The type strain is CCBAU 85039(T) (=LMG 24453(T) =CGMCC 1.7071(T)). The DNA G+C content of this strain is 59.7 mol% (T(m)).