Interactions of trace metals with bacteria and fungi in selected agricultural soils of Egbema Kingdom, Warri North, Delta state, Nigeria

This study was aimed at investigating the relationship of trace metals with prevalence of bacteria and fungi in polluted farmland of Egbema Kingdom, Delta state. This may contribute to the knowledge on the influence of the microorganism to the arability of agricultural soil from an ecotoxicological viewpoint. Soil samples were analyzed for physico-chemical parameters and trace metals using atomic absorption spectrophotometer (Buck Scientific, 210VGP). The samples were also screened for fungi and bacteria isolates. Trace metals (Fe, Zn, Cd, Ni and Cu) determined in the agricultural soils of Egbema kingdom were below WHO limits. The fungi species with the highest number of occurrence was Aspergillus niger, while the species with the lowest occurrence were Fusarium oxsporium, Penicillium dirty white, and Penicillium sp. The order of abundance of fungi across the stations was Station 2> Station 4> Station 3> Station 1> Station 7> Station 5> Station 6> Station 9> Station 8. The bacteria species with the highest number of occurrence was Proteus sp I, while the species with the lowest occurrence was Alcaligenes sp. which occurred only once at Station 5. The order of abundance of bacteria in the soil samples across the stations was Station 4> Station 3> Stations 5 and 9> Station 2> Station 8> Station 7> Station 6. All trace metals in the agricultural soils of Egbema kingdom were below WHO limits. Fe, Zn, Cd and Ni showed no relationship with the microbial contents of the soil. Various strains of fungi and bacteria (gram positive and gram negative) were observed in the soil samples. An antagonistic relationship was observed between bacteria and fungi. Significant positive correlation occurred between the concentration of copper and bacteria counts indicating that the concentration of copper in the soil might have enhanced the abundance of bacteria in the soil, vice versa. The bacteria might be a promising tool in regulation of soil copper concentration

Development of Mass-Conserving Atomistic Mathematical Model for Batch Anaerobic Digestion: Framework and Limitations

A variety of mathematical models have been developed to simulate the biochemical and physico-chemical aspects of the anaerobic digestion (AD) process to treat organic wastes and generate biogas. However, all these models, including the most widely accepted and implemented Anaerobic Digestion Model No.1, remain incapable of adequately representing the material balance of AD and are therefore inherently incapable of material conservation. The absence of robust mass conservation constrains reliable estimates of any kinetic parameters being estimated by regression of empirical data. To address this issue, the present work involved the development of a “framework” for a mass-conserving atomistic mathematical model which is capable of mass conservation, with a relative error in the range of machine precision value and an atom balance with a relative error of ±0.02% whilst obeying the Henry’s law and electroneutrality principle. Implementing the model in an Excel spreadsheet, the study calibrated the model using the empirical data derived from batch studies. Although the model shows high fidelity as assessed via inspection, considering several constraints including the drawbacks of the model and implementation platform, the study also provides a non-exhaustive list of limitations and further scope for development

Development of Mass-Conserving Atomistic Mathematical Model for Batch Anaerobic Digestion: Framework and Limitations

A variety of mathematical models have been developed to simulate the biochemical and physico-chemical aspects of the anaerobic digestion (AD) process to treat organic wastes and generate biogas. However, all these models, including the most widely accepted and implemented Anaerobic Digestion Model No.1, remain incapable of adequately representing the material balance of AD and are therefore inherently incapable of material conservation. The absence of robust mass conservation constrains reliable estimates of any kinetic parameters being estimated by regression of empirical data. To address this issue, the present work involved the development of a “framework” for a mass-conserving atomistic mathematical model which is capable of mass conservation, with a relative error in the range of machine precision value and an atom balance with a relative error of ±0.02% whilst obeying the Henry’s law and electroneutrality principle. Implementing the model in an Excel spreadsheet, the study calibrated the model using the empirical data derived from batch studies. Although the model shows high fidelity as assessed via inspection, considering several constraints including the drawbacks of the model and implementation platform, the study also provides a non-exhaustive list of limitations and further scope for development

Volatile Fatty Acids Effective as Antibacterial Agents against Three Enteric Bacteria during Mesophilic Anaerobic Incubation

The antibacterial effects of a selection of volatile fatty acids (acetic, propionic, butyric, valeric, and caproic acids) relevant to anaerobic digestion were investigated at 1, 2 and 4 g/L. The antibacterial effects were characterised by the dynamics of Enterococcus faecalis NCTC 00775, Escherichia coli JCM 1649 and Klebsiella pneumoniae A17. Mesophilic anaerobic incubation to determine the minimum bactericidal concentration (MBC) and median lethal concentration of the VFAs was carried out in Luria Bertani broth at 37 °C for 48 h. Samples collected at times 0, 3, 6, 24 and 48 h were used to monitor bacterial kinetics and pH. VFAs at 4 g/L demonstrated the highest bactericidal effect (p < 0.05), while 1 g/L supported bacterial growth. The VFA cocktail was the most effective, while propionic acid was the least effective. Enterococcus faecalis NCTC 00775 was the most resistant strain with the VFAs MBC of 4 g/L, while Klebsiella pneumoniae A17 was the least resistant with the VFAs MBC of 2 g/L. Allowing a 48 h incubation period led to more log decline in the bacterial numbers compared to earlier times. The VFA cocktail, valeric, and caproic acids at 4 g/L achieved elimination of the three bacteria strains, with over 7 log10 decrease within 48 h

Effect of the Inoculum-to-Substrate Ratio on Putative Pathogens and Microbial Kinetics during the Batch Anaerobic Digestion of Simulated Food Waste

The effects of the inoculum (anaerobic digestion effluent) to substrate (simulated food waste) ratio (ISR) 4.00 to 0.25 on putative pathogens and microbial kinetics during batch mesophilic anaerobic digestion were investigated. Red fluorescent protein labelled (RFPAKN132) Escherichia coli JM105 was introduced as a marker species, and together with the indigenous Clostridium sp., Enterococcus sp., Escherichia coli, and total coliforms were used to monitor pathogen death kinetics. Quantitative polymerase chain reaction was also used to estimate the bacterial, fungal, and methanogenic gene copies. All the ISRs eliminated E. coli and other coliforms (4 log10 CFU/mL), but ISR 0.25 achieved this within the shortest time (≤2 days), while ISR 1.00 initially supported pathogen proliferation. Up to 1.5 log10 CFU/mL of Clostridium was reduced by acidogenic conditions (ISR 0.25 and 0.50), while Enterococcus species were resistant to the digestion conditions. Fungal DNA was reduced (≥5 log10 copies/mL) and was undetectable in ISRs 4.00, 2.00, and 0.50 at the end of the incubation period. This study has demonstrated that ISR influenced the pH of the digesters during batch mesophilic anaerobic digestion, and that acidic and alkaline conditions achieved by the lower (0.50 and 0.25) and higher (4.00 and 2.00) ISRs, respectively, were critical to the sanitisation of waste

Assessment of Anaerobic Digestate Amended with Wood Ash and Green Vegetable Matter and Impacts on Microbial Growth

Anaerobic digestion (AD) is a waste management method worldwide, that results in biogas and digestate production. The digestate remains is a potential biofertilizer but may fall short of vital nutrients required for optimal plant growth, hence, requires amendment with other biomass residues. This study was aimed at investigating the microbial quality of digestate amended with wood ash and vegetable matter during treatment. Digestate from cattle rumen content (CR), food waste (FW), fruit waste (FRW) and their combinations were amended with wood ash, vegetable (green) matter and a blend of both. Amendment was carried out for 5 weeks, and samples were analyzed weekly. Enumeration and identification of bacteria and fungi were carried out on culture media. The rhizobacterial potential of the identified bacterial isolates was also investigated using standard microbiological procedures. The results showed high bacterial and fungal load in vegetable amended digestate from the first to the fourth week. Comparatively, cattle rumen content and food waste digestate amended with vegetables were highly significant, with mean values of 0.8 and 0.6, respectively. The identified bacterial isolates namely, Bacillus subtilis, Salmonella sp, Pseudomonas sp, Proteus sp, Enterobacter sp, Chromobacterium sp Bacillus spp. and Escherichia coli were found to be involved in the solubilization of phosphate, nitrogen fixation, ammonia production and induction of indole acetic acid. Specifically, feedstocks amended with vegetable (green) waste was found to have a significant influence on microbial growth (bacterial and fungal loads) between week 1 and 4. This suggests that digestate amendment is a crucial recipe for microbial growth which has considerable benefits in nutrient enhancement and increase in carbon levels