New insights into the metagenomic link between pre‐treatment method, addition of an inoculum and biomethane yield during anaerobic digestion of water hyacinth (Eichhornia crassipes)

Abstract

BACKGROUND Water hyacinth (Eichhornia crassipes) is a fast growing water weed that threatens the aquatic ecosystem and human activities, hence control of the plant is essential. One such control approach is to harvest and utilize hyacinth as a substrate for anaerobic digestion (AD). Various factors influence AD performance, including substrate pre‐treatment and microbial community composition, amongst others. This study was aimed at establishing the link between method of substrate pre‐treatment, microbial diversity, inoculum addition and biogas yield during AD of hyacinth. RESULTS The addition of an inoculum resulted in microbial community stability and early biomethane production of up to 0.4 L irrespective of pre‐treatment method. However, cultures that lacked inoculum showed distinct microbial community structure variation in response to pre‐treatment method, and minimal early biomethane production (up to 0.1 L). Biogas produced by cultures lacking inoculum was initially mostly composed of carbon dioxide (up to 100% of total biogas), but as digestion proceeded, an increase in biomethane production was observed (up to 60% of total biogas), which correlated with the shift in microbial community structure and increased microbial diversity. This indicates the presence of biogas‐producing microorganisms associated with the collected hyacinth. Canonical correspondence analysis proved that dynamic changes in microbial community structure and biogas yield were strongly correlative. CONCLUSION This study proves that hyacinth pre‐treatment influences microbial community structure and concomitant biogas yield in the absence of an inoculum. The addition of an inoculum aids in stability of microbial community structure and biogas yield irrespective of method of hyacinth pre‐treatment. © 2019 Society of Chemical Industry

The Multifaceted Function of Water Hyacinth in Maintaining Environmental Sustainability and the Underlying Mechanisms: A Mini Review

“…The growth of the microbial community is affected by reaction parameters including pH, temperature, and nutrient balance, such as the C/N ratio. Thus, the microbiome changed along with the alternations of these parameters during AD [ 133 , 134 ]. To further enhance sustainability, WH is often co-digested with other plant biomass, animal dung and other wastes [ 135 , 136 ].…”

Invasive Water Hyacinth: Ecology, Impacts and Prospects for the Rural Economy

“…However, Photong and Wongthanate [ 108 ] demonstrated that cumulative methane production is higher when the process occurs at a thermophilic temperature of 55 °C (230 mL/g COD methane produced), compared to a mesophilic temperature (methane production at 110 mL/g COD ). Methane yield rises at higher temperatures have been linked to lower enzyme activation energy, higher hydrogen production, stable consortia population and increased methane cumulative production [ 109 , 110 , 111 ]. Overall, many processes involved in anaerobic digestion are biochemical and highly dependent on the reaction rates of the enzymes involved [ 106 ].…”

“…Inoculum starter is a prerequisite at the commencement of the digestion process; however, subsequent processes may occur without the addition of inoculum. Nevertheless, the absence of inoculum causes more dynamic variations in the microbial community, leading to increased lag time and lower biomethane concentration, regardless of pre-treatment [ 111 ]. From the perspective of rural communities planning to adopt the AD approach to treat their agricultural or municipal waste, the use of inoculum is an interesting opportunity, as locals could use any available inoculum source from their economic activities, such as waste from cow-herding, poultry farming or fishing.…”

Bioaugmentation potential of inoculum derived from anaerobic digestion feedstock for enhanced methane production using water hyacinth

“…In addition to the aforementioned qualities, low lignin content of water hyacinth and its possession of plants’ essential nutrients make it a suitable substrate for efficient production of biogas and soil ameliorant (Njogu et al 2021 ; Barua and Kalamdhad 2019 ). The use of water hyacinth to generate biogas is an eco-friendly and innovative means of managing this intrusive aquatic weed (Roopnarain et al 2019 ). Water hyacinth is a menace in the aquatic environments as its rapid proliferation hinders many biological and socioeconomic activities where they are resident (Honlah et al 2019 ).…”

“…However, the use of water hyacinth as a potential inoculum to enhance biogas production is yet to be investigated. A study that reported that biogas-producing microorganisms are innately linked to water hyacinth harvested from the Hartbeespoort dam in South Africa motivated the investigation into the potential of these microorganisms as an inoculum (Roopnarain et al 2019 ).…”