Methane-driven nitrate removal and identification of active bacterial species using RNA-SIP and Hight-throughput sequencing.

Nitrate pollution in water can potentially be mitigated by aerobic and microaerobic microbial methane oxidation coupled to nitrate removal. This research has recently attracted interest due to the key role oxygen concentration plays in the process. Although seen as potential means of removing nitrate from contaminated waters, the mechanism and microorganisms involved in the process are still poorly understood. The study seeks to investigate the nitrate removal potential of the process by answering the “who does what?” question in the process by identifying the active bacterial species by combining the RNA stable isotope probing (RNA- SIP) technique with high-throughput sequencing. In this study, methanotrophic biofilms were enriched in columns packed with 3 mm glass beads. The columns were made from acrylic tube 50 mm in diameter, and 400 mm in length and a working volume of 0.0004 m3. The CH4 and O2 gas feed into the aerobic column was 2% v/v CH4 in air while the microaerobic gas feed for the two columns was 2% CH4, 2% O2 and 96% Ar, and 2% CH4, 2% O2 and 96% N2. The gases were continuously fed into the columns and nitrate mineral salt (NMS) with a nitrate concentration of 140 mg∙L-1 NO3—N was recirculated through the columns and replaced when exhausted. The aerobic and microaerobic reactors were operated for 238 and 122 days respectively. The methane oxidation rate observed under both aerobic and microaerobic condition differed with the aerobic columns giving an average methane oxidation rate of 62.8±21.45 gCH4∙m-3hr- 1 for the aerobic column while the microaerobic columns gave an average rate of 10.67 ±3.9 (Ar) and 9.28 ±3.5 gCH4∙m-3hr-1 (N2) respectively. Nitrate removal rates observed for the columns showed that the microaerobic columns gave a maximum rate of 3.6 gN m-3h-1, while the aerobic column gave a maximum rate of 0.8 gN m-3h-1. The CH4/NO3 consumption ratio obtained from the columns showed that the average consumption ratio in the aerobic columns was 4.3 ±1.6, while the microaerobic columns gave a consumption ratio of 2.6 ±1.1 (Ar) and 2.2 ±0.8 (N2) respectively. Oxygen concentration and O2/CH4 ratio between the aerobic and microaerobic columns is thought to have played an important role in methane oxidation rates and nitrate removal rates. In addition, the production of ammonium in the aerobic column is also suggested to play a role in the low nitrate removal rate observed in the aerobic columns. RNA-SIP in combination with high-throughput sequencing identified the active bacterial species that were the key players in the methane-driven denitrification process under aerobic conditions. The bacterial genera Methylocystis and Methylosinus were identified as the main methane oxidizers under both aerobic and microaerobic conditions, producing organic intermediates such as methanol, acetate and formate that were identified. These were hypothesised to drive nitrate removal. Active denitrifiers whose 16S rRNA were enriched with 13C-labeled substrate and were considered the major players were Hyphomicrobium, Pseudoxanthomonas, Arenimonas, and Methyloversatilis

Phytochemistry and Antimicrobial Properties of 2:1 and 1:2 Ethanol-methanol Extracts of Tetrapleura Tetraptera

Tetrapleura tetraptera (Aidan)-an African medicinal plant was analysed for its phytochemicals and its antimicrobial activity using 1:2 and 2:1 ethanol-methanol as solvents for extraction. Amongst the phytochemicals present in the plant, oxalates, cyanogenic glycosides, tanins and phytic acids were quantified. The solvents produced different degrees of extraction of these phytochemicals as well as their antimicrobial activity. The 2:1 methanol: ethanol solvent extracted 1.425%, 0.70 mg/100g, 0.315 mg/100g, 10.805 mg/100g and 0.50% while the 2:1 ethanol: methanol solvent extracted 5.43%, 0.705 mg/100g, 0.52 mg/100g, 7.365 mg/100g and 0.635% of oxalates, cyanogenic glycosides, tanins and phytic acids respectively. Considering the antimicrobial activity of the 1:2 ethanol: methanol extracts. There was a corresponding decrease in susceptibility with decrease in the concentration of the extract indicating that the concentration of the plant extract has an effect on the isolates. The results also revealed that the isolates were all sensitive to high concentrations of 250mg/ml and 125mg/ml of the plant extract but demonstrated varied response to the 62.5mg/ml and 31.25mg/ml of the plant extract. On the other hand, the 2:1 ethanol: methanol extract was also characterized by a low activity at a low concentration of 31.25mg/ml and 62.5mg/ml. The Ethanol: methanol 2:1 extract of T. tetraptera is a better extraction method than the 1:2 ethanol: methanol extract as demonstrated by the phytochemistry and antimicrobial activity of the plant

Sustainable Waste-to-Energy Technologies: Bioelectrochemical Systems

The food industry produces a large amount of waste and wastewater, of which most of the constituents are carbohydrates, proteins, lipids, and organic fibers. Therefore food wastes are highly biodegradable and energy rich. Bioelectrochemical systems (BESs) are systems that use microorganisms to biochemically catalyze complex substrates into useful energy products, in which the catalytic reactions take place on electrodes. Microbial fuel cells (MFCs) are a type of bioelectrochemical systems that oxidize substrates and generate electric current. Microbial electrolysis cells (MECs) are another type of bioelectrochemical systems that use an external power source to catalyze the substrate into by-products such as hydrogen gas, methane gas, or hydrogen peroxide. BESs are advantageous due to their ability to achieve a degree of substrate remediation while generating energy. This chapter presents an extensive literature review on the use of MFCs and MECs to remediate and recover energy from food industry waste. These bioelectrochemical systems are still in their infancy state and further research is needed to better understand the systems and optimize their performance. Major challenges and limitations for the use of BESs are summarized and future research needs are identified