Enrichment and balancing of nutrients for improved methane production using three compositionally different agro-livestock wastes: Process performance and microbial community analysis.

Balanced nutrition is important for maximizing anaerobic digestion (AD) performance. Herein, the strategy of balancing sugar-fiber-nitrogen nutrients was first established for improved methane production by co-digesting two agricultural and one livestock wastes with complementary compositional properties, such as banana pseudo-stem (BPS), sugarcane baggage (SCB), and chicken manure (CM) having high sugar, fiber and nitrogen contents, respectively. The maximum methane yield was 186.5 mL/g VSadded with a mixture of 45.7% BPS, 26.2% SCB and 28.1% CM (with 1: 11.3: 0.3 of sugar to fiber to nitrogen ratio), increasing by 16.1%, 53.3%, 122.6% than those of mono- BPS, SCB, and CM, respectively. The co-digestion process remained stable under an organic load of 4 g VS/(L·day), which was attributed to the predominant presence of Bacteroidetes, Proteobacteria, Thauera, uncultured_bacterium_p_Aegiribacteria, and hydrogenotrophic methanogens. This study provides a deeper understanding of the co-digestion with agricultural and livestock wastes from the perspective of nutrient balance.

Synergistic digestion of banana pseudo-stems with chicken manure to improve methane production: Semi-continuous manipulation and microbial community analysis.

This study aimed to investigate the interactions between banana pseudo-stems (BPS) and chicken manure (CM) during anaerobic co-digestion (AcoD) in batch and semi-continuous experiments. The batch experiments results showed that the methane yield was the highest (193.7 mL/g VS) in AcoD with BPS: CM ratio of 4:1, which was increased by 57.2% and 66.1%, respectively. Semi-continuous experiments revealed that AcoD resulted in higher methane production. Monitoring of the system parameters indicated that AcoD could better adapt to the increasing organic loading rate, with better system stability and methane production efficiency. The microbial analysis illustrated that AcoD increased the relative abundance of hydrolytic bacteria such as Firmicutes, Patescibacteria, and Bacteroidetes. With regard to archaea, AcoD improved the abundance of Methanosaeta, the major acetoclastic methanogens. These changes in the microbial flora allowed AcoD to remain stable while efficiently producing methane and improved the BPS and CM processing efficiency.

Site-saturation mutagenesis at amino acid 329 of Klebsiella pneumoniae halophilic α-amylase affects enzymatic properties.

Halophilic α-amylases possess optimal activity in high salt concentrations. Therefore, they can be used in many extreme conditions in industrialised production. In the present work, a halophilic α-amylase (KP) from Klebsiella pneumoniae was characterised, and it exhibited a high specific activity of 3512 U/mg under optimal conditions of 2 M NaCl at 50°C and pH 6.5, but only 97 U/mg in the absence of salt. Furthermore, threonine at position 329 (Thr-329) was found to be related to the non-halophilic properties of KP according to PCR-based site-saturation mutagenesis. The activity of a mutant KP in which this threonine was replaced by aspartic acid was improved 14.6-fold compared with the native enzyme under salt-free conditions, and was increased by 14.8% in the absence of salt. Additionally, the optimal enzymatic properties of KP, including pH and temperature, were altered very little by the amino acid replacement. A further three halophilic α-amylases displayed similar mutational results. The findings provide a reference for bidirectional transformation of KP and similar halophilic enzymes.

Evaluation of squeezing pretreatment for improving methane production from fresh banana pseudo-stems.

Banana pseudo-stems (BPS) are an abundant and low-lignin-content lignocellulosic biomass for methane production. However, the high-water content in BPS increases the transport costs, and the resistant structure of BPS hinders methane production. In this study, squeezing of BPS as a pretreatment was evaluated for improving anaerobic digestion (AD). After 20-d digestion, methane production from squeezed BPS was 204.2 ± 6.2 mL/(g volatile solids (VS) of feedstock), which was 41.2% more than that from untreated BPS. This increase was mainly attributed to the improvement of physical properties (e.g. water absorbing capacity) and the change in the resistant structure of BPS after squeezing, which promoted good contact between microbes and substrate during AD. The measured methane production was described using a modified Gompertz model and the results showed that anaerobic process would take less time and occur faster when pretreated BPS was used as the substrate. The energy produced during AD of squeezed BPS, after deducting the energy used by the squeezer, resulted in an energy surplus of 26.2%.

A novel hydraulic biogas digester controlling the scum formation in batch and semi-continuous tests using banana stems.

Scum formation is a widespread phenomenon and causes serious damage in straw biogas digesters. A 10-L novel hydraulic conical digester for controlling scum was developed in this work and compared with a hydraulic cylindrical digester that simulated the conventional digester. After 30 d of batch and 120 d of semi-continuous fermentations using banana stems, the scum volumes of in cylindrical digesters were 4.12 and 2.12 times that in the conical digesters, respectively. The conical digesters increased biogas production by 5.7% and 11.6% in batch and semi-continuous tests, respectively. The VS removal of feedstock in conical digesters were 5.6 and 7.2% greater than for the batch and semi-continuous cylindrical, respectively. The microbial diversity and evenness were higher in conical than cylindrical digesters. The results demonstrated that conical shape was an effective structure for controlling scum formation and improving biogas production.