Effect of biological treatment of pig dung using Pseudomonas fluorescens on biogas production

Introduction

India's energy production is experiencing significant growth, with an annual increase of 7.06%, reaching 1,739.1 billion units in 2023-24 (CEA, 2024). Despite this progress, there remains a shortfall of 4.1 billion units needed to meet the nation's energy demands, primarily due to rising population and industrialization. This situation has led to a heightened interest in exploring new and renewable energy sources such as solar, wind, tidal, and biogas. In addition, India has the largest livestock population globally, estimated at 535.78 million in 2019. It also ranks third in sheep production, with a total sheep population of 74.26 million (BAHS 2024). The vast amounts of animal manure generated present both challenges and valuable opportunities for energy production through biogas, derived from the anaerobic digestion of organic materials. This eco-friendly technology has gained traction over the last decade for its effectiveness in waste management and clean energy generation (Romero-Güiza et al. 2016) [9] . By harnessing biogas, India can effectively address its energy shortfall, improve waste management practices, and promote sustainable energy solutions, all contributing to a healthier environment. Therefore, the current study aims to evaluate the impact of biological treatment of sheep dung using Pseudomonas fluorescens on biogas production.

Materials and Methods

Work plan

For this experiment, fresh sheep dung from a uniform age group of animals was utilized as the substrate. It was analysed for proximate principles as represented in Table 1 and standardized to contain 10% dry matter before its introduction into the digester to enhance the efficiency and yield of biogas generation A slurry was prepared by adding the appropriate amount of water to have dry matter content of 10%. To this mixture, inoculum of Pseudomonas fluorescens was introduced at concentrations of 3% and 6% as detailed in Table 2. The treatment groups were designated as S0 (control), S3 (3% inoculum), and S6 (6% inoculum). The prepared syringes containing 20 ml of this slurry were then incubated in a water bath at 30 °C, the optimal temperature for the growth of Pseudomonas fluorescens.

Biogas production was monitored over a 50-day period, with each treatment group having three replicates. Every 10 days, six syringes from each group were collected for fiber analysis and bacterial quantification using qPCR techniques.

Statistical analysis

Data analysis was conducted using SPSS software, version 16.0. A one-way ANOVA was performed to evaluate differences between treatment groups, with significance determined at the 5% level as per Snedecor and Cochran (1994). The Duncan Multiple Range Test (DMRT) was used for further comparison of significant differences. Overall, cumulative biogas production steadily increased for all treatments, with S6 (6% inoculum) generating 8.98% more biogas compared to the control group (S0), while S3 (3% inoculum) produced 7.77% more than the control.

Results and Discussion

Discussion

During the first 10 days, there were no significant differences (p>0.05) in cumulative gas yields among the control group (S0) and the 3% (S3) and 6% (S6) culture-treated groups. This likely reflects a short lag phase for the methanogenic bacteria, resulting in a relatively slow start of the hydrolytic processes. However, from days 21 to 30 onward, the 6% culture group (S6) showed significantly higher cumulative gas production (p < 0.05) compared to the controls. This trend continued through day 50, with the 6% treatment consistently outperforming both the control and the 3% treatments. The findings of this research indicate that a 6% inoculum of Pseudomonas fluorescens can enhance biogas yield in sheep manure in a reproducible and dose-dependent manner. In contrast, the 3% inoculum did not reach the necessary threshold for significant improvement. Specifically, the sheep dung treated with the 6% inoculum yielded 8.92% more biogas, while the 3% treatment produced 7.79% more compared to the control. This improved production at the 6% level can be attributed to enhanced hydrolysis of readily degradable organic compounds and partial degradation of lignocellulose.

Pseudomonas fluorescens produces beneficial enzymes, including dyp-type peroxidases (Rahmanpour and Bugg, 2014) and endo-β-1,4-glucanase and exo-β-1,4-glucanase (Pathak et al., 2016) [7] , which facilitate the breakdown of lignin and increase the accessibility of cellulose and hemicellulose.

The lack of significant enhancement at the 3% inoculum level suggests that a critical threshold of bacterial biomass or enzyme activity was not reached, limiting substrate modification and biogas yield. Similar findings were noted by Bruni et al. (2010) [1] , who reported that suboptimal dosing of microbial cultures had negligible effects on methane production. The delayed response observed in sheep dung where significant improvements were noted only from days 21 to 30 can be explained by the lower availability of soluble, readily degradable nutrients in sheep manure. This is due to the higher digestibility of sheep diets, which leaves less soluble substrate for immediate microbial action. Research by Li and Triolo et al. (2011) [10] emphasized that differences in manure composition and prior digestibility influence biogas yield, resulting in lower or delayed responses to biological treatment. Similar findings have been reported by Mustafa et al. (2016) [6] , who observed a 120% increase in yield compared to unprocessed rice straw, and Fugol et al. (2023) [4] , who noted a 62% increase in biogas production from maize silage treated with Pseudomonas spp. compared to the control

Conclusion

The present study suggests that inoculation of sheep dung slurry with Pseudomonas fluorescens showed significant enhancement in biogas yield at 6% inoculum than compared to 3% and control.

Acknowledgement

We are grateful to our Dean, Veterinary college Bengaluru, and KVAFSU, Bidar, Karnataka for providing necessary facilities and funding to carry out this research work.

References

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