A group of researchers at King Juan Carlos University in Spain have discovered a new method to convert industrial wastewater and household sewage into energy using purple phototropic purple bacteria (PPB) as a battery.
In the recent study, published in the journal Frontiers in Energy Research, the scientists explained that the energy-storing bacteria are capable of recovering almost 100% of the carbon from each type of organic waste and when supplied with an electric current, the PPB can generate hydrogen gas to produce electricity.
In a statement, Daniel Puyol, co-author and PhD said that while high carbon emissions have been one of the biggest problems of current wastewater treatment plants, their light-based bio-refinery process could provide a way to derive clean energy from wastewater, leading to zero carbon footprint. With highly diverse metabolism, PPB can make an ideal tool for recovering energy resources from organic waste, he added.
The research team analyzed the optimal conditions on which hydrogen production of a mixture PPB species could be maximized and tested the impact of a negative current on the metabolic characteristics of the organism. The major breakthrough of the study occurred when the researchers discovered the nutrient blend that can generate highest rate of hydrogen production while reducing the carbon dioxide production.
The findings demonstrated that PPB can be employed to recover valuable organic matter such as sodium glutamate and malic acid, typically found in industrial waste water, according to co-author Abraham Esteve-Núñez. They also found out that PPB has the ability to capture carbon dioxide during photosynthesis, using electrons from a negative electrode.
Instead of CO2 and water, the purple bacteria uses nitrogen gas and organic molecules to provide carbon, nitrogen, and electrons essential for photosynthesis, making them grow quicker than other phototrophic bacteria and algae. In addition, this type of bacteria can produce hydrogen gas and a type of biodegradable polyester as byproducts of the metabolic functions. However, which product predominates is determined by the environmental conditions of the bacteria including temperature, light intensity, and types of nutrients and organic materials available.
The researchers manipulated the environmental conditions to tune PPB’s metabolism to varying applications, depending on market requirements and source of the organic waste. Esteve-Núñez said that the unique approach of the study is using an external electric current to evaluate the productive output of PPB.
As metabolic pathways in PPB are connected by a common currency, electrons, it can process a bioelectrochemical system. Like battery, electron flow within the bacteria can be optimized to maximize the rate of systhesis. The researchers are now planning to create a technique that can increase the hydrogen production by donating electrons from cathode to the metabolic pathways of the purple bacteria.