Whether the sewage is full of “waste” is a matter of perspective.
“Why is it a waste?” asked Zhen (Jason) He, a professor at Washington University in St. Louis. “They are organic materials,” he said, and those can provide energy in a number of ways.
Then there is the other valuable resource in wastewater.
His laboratory has developed a system that recovers both, filtering the wastewater while generating electricity. The results of the reference-scale trials were published in May and featured as a cover story in the journal. Environmental Sciences: Water Research and Technology.
The waste materials in the sewage are full of organic materials that, for the bacteria, are food.
“Bacteria love them and can turn them into things we can use,” he said. “Biogas is the main source of energy that we can recover from wastewater; the other is bioelectricity ”.
Egyptian researchers working with him are interested in using similar technological platforms for water desalination.
There are already ways to harness bacteria to produce energy from wastewater, but these methods often do so at the expense of water, which could be filtered and otherwise used, if not for drinking, for “gray water” purposes, such as irrigation. and flushing the toilet.
His laboratory took the two processes, filtration and energy production, and combined them, integrating the filtration system into the anode electrode of a microbial electrochemical system.
The system is configured like a typical microbial fuel cell, a bacterial battery that uses electrochemically active bacteria as a catalyst where a traditional fuel cell would use platinum. In this type of system, bacteria adhere to the electrode. When the wastewater is pumped to the anode, the bacteria “eat” the organic materials and release electrons, creating electricity.
However, filtering that same water requires a different system.
His lab combined the systems, developing a permeable anode that acts as a filter.
The anode is a dynamic membrane, made of conductive carbon cloth. Together, bacteria and the membrane filter 80% to 90% of organic materials, leaving the water clean enough to be released to nature or further treated for non-potable water uses.
He used a mixed culture of bacteria, but they had to share one characteristic: the bacteria had to be able to survive in an environment without oxygen.
“If there was oxygen, the bacteria would just throw electrons at the oxygen, not the electrode,” he said. “If you can’t breathe with the electrode, you will die.”
To find the right bacteria, for the most part, give in to nature.
“It is not 100 percent natural, but we select those that can survive in this condition,” he said. “It’s more like ‘designed selection,'” the bacteria that survived and breathed with the electrode were selected for the system.
The amount of electricity generated is not enough to, say, power a city, but in theory it is enough to help offset the substantial amount of energy used in a typical US water treatment plant.
“In the United States, about 3% to 5% of electricity is used for water and wastewater activity,” he said. Considering the use of a local municipal plant, he believes that his system can significantly reduce energy consumption.
“Wastewater is a resource in the wrong location.”
“Normally, the process consumes around 0.5 KWH of electricity per cubic meter,” he said. Based on bench-scale experiments, “We can cut it in half or more.”
But main objective of the He system It is not electricity production, it is wastewater treatment and nutrient recovery.
“Bacteria can turn those organic materials into things that we can use,” he said. “We can also recover nutrients such as nitrogen or phosphorous for fertilizers. We can use it to feed plants. Only when we don’t use it does it become a waste. “
Fountain: Washington University in St. Louis; featured image, Patrick Brossett, CC license
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