Stoichiometry and kinetics of the PHB-producing Type II methanotrophs Methylosinus trichosporium OB3b and Methylocystis parvus OBBP.

Methane is classified as the second major greenhouse gas with a global warming potential 25 times higher than carbon dioxide. Wastewater treatment plants (WWTPs) are considered as one of the main anthropogenic sources for global methane emissions. Utilizing the anaerobic digestion driven biogas, methanotrophs can offer a prominent solution for coupling methane mitigation with value-added resources recovery. Hence, methanotrophs can play a pivotal role in the paradigm shift to consider wastewater streams as proactive energy and value-added material resource instead of waste requiring further treatment. This review is destined to summarize the recent accomplishments in three methanotrophic-based biotechnological applications which are methanol, biopolymers production and biological nitrogen removal processes. Moreover, methanotrophs taxonomy, metabolism, and growth conditions are reviewed. In addition, the possibility to link the aforementioned applications within the operation of existing WWTPs in order to transform “energy-consuming treatment processes” into “energy-saving and energy-positive systems” is discussed.

Sustainable biogas mitigation and value-added resources recovery using methanotrophs intergrated into wastewater treatment plants

Optimization of methane bio-hydroxylation using waste activated sludge mixed culture of type I methanotrophs as biocatalyst

Behavior of type II methanotrophic bacteria enriched from activated sludge process while utilizing ammonium as a nitrogen source

Wastewater treatment plants contribute to the global warming phenomena not only by GHG emissions, but also, by consuming enormous amount of fossil fuel based energy. Therefore, methane bio-hydroxylation has attracted the attention as methanol is an efficient substitute for methane (GHG) due to its transportability and higher energy yield. 
This work is destined to investigate and optimize the factors affecting the microbial activity within methane bio-hydroxylation system using type I methanotrophs enriched from activated sludge system. The optimization resulted in a notable enhancement of the growth kinetics. The attained maximum specific growth rate (max) (0.358 hr-1) and maximum specific methane biodegradation rate (qmax) (0.605 g-CH4,Total/g-DCW/hr-1) were the highest reported in mixed cultures. Furthermore, the maximum methanol productivity achieved is comparable with pure cultures and equal to 211581 mg/L/day. Whereas, methanol concentration of 48521 mg/L was attained which is two times higher than the reported using mixed culture.

Biological Conversion Process of Methane into Methanol Using Mixed Culture Methanotrophic Bacteria Enriched from Activated Sludge System

Methanotrophic bacteria grow aerobically using methane as a source of carbon and energy. They are widespread in the environment and play an important role in oxidizing methane in the environment, thereby mitigating the effects of global warming by this potent greenhouse gas. Methane monooxygenases (MMOs), which are the enzymes that catalyze the oxidation of methane, especially, the catalytically versatile soluble MMO, can cooxidize a wide range of hydrocarbons and chlorinated hydrocarbons, and have great potential as biocatalysts for bioremediation and biocatalysis. Methanotrophs can also be used to make single-cell protein from methane. Recent isolation of novel groups of thermophilic, acidophilic methanotrophs has revealed that these bacteria can even grow under extreme environmental conditions. The availability of genome sequences of several methanotrophs now opens up possibilities of postgenomic studies to investigate the regulation of methane oxidation in the laboratory and in the environment.

Y. A. Trotsenko

Papers

Physiology and biochemistry of the aerobic methane oxidising bacteria.