People don’t like to think about what happens to the waste they flush down their toilets. But for many engineers and microbiologists, these plants are a hotbed of scientific advances, inspiring their trade organization to propose a name change to “water resource recovery facility.”
The wastewater from our sinks, toilets, showers laundry machines and dishwashers can be turned into valuable yields with the help of studies on unique bacteria – some of which were discovered accidentally recently during the 1990s.
These laggards to the research scene, called anammox bacteria, are the topic of a new study headed by Daniel Noguera and Katherine McMahon, professors of Civil and Environmental engineering at the University of Wisconsin-Madison. Outcomes of their investigation were published in the journal Nature Communications.
The name given to these bacteria reflects its function. Ammonium is converted into nitrogen gas under anaerobic conditions. Researchers and treatment plant operators are thrilled about these microbes because they have the potential to save a huge amount of money.
Noguera said it was important to be able to remove ammonium anaerobically because 50 per cent of sewage plant’s operating cost was pumping oxygen into the river. He also stated that some of this oxygen
It is observed that these anammox bacteria can’t do their job in isolation. They are part of a community, just like the intricate microbiome in our gut that breaks down food and keeps us healthy. The subject of the new study was this community which co-existed with anammox bacteria.
Noguera said that they knew very little about the role of bacteria that co-exist in anammox granules. He stated that for the first time, their study identified complete gene expression levels in these granules which provided important clues on what the anammox bacteria and their community might actually be doing, and how they intermingle.
These community are heterotrophs, since they depend on the anammox bacteria – which are primary autotrophs, capable of photosynthesis – to turn atmospheric carbon dioxide into organic carbon. Among the most fascinating results of the new study are hypotheses for the exchange of biochemical material between these two groups of microbes.
The heterotrophs receive the organic carbon they need to grow from the anammox bacteria in the form of several specific molecules, the researchers discovered in the study. In return, the heterotrophs convert nitrogen into a form that anammox bacteria require for growth. They sustain in mutually beneficial relationship.
A conventional wastewater treatment plant converts ammonium, which is toxic to aquatic species, into nitrogen gas and nitrate. Nitrogen gas is expelled into the atmosphere, while nitrate, an important plant nutrient, stays within the treated water. Regulations on the amount of nitrate that may be expelled vary by state, but excess nitrate creates algal blooms in natural bodies of water, depleting oxygen levels for aquatic organisms.
An added advantage of anammox bacteria, compared to conventional wastewater treatment, is that they convert a larger amount of ammonium to nitrogen gas.
Treatment plant workers now have to weigh the benefits of these new microbes against their implementation challenges. Anammox bacteria grow very slow, taking about seven days to double in number. And they require closely monitored oxygen and temperature which increases operational complexity.
But anammox reactors are not the only option for the treatment plant of the future to extract valuable resources from wastewater. In fact, some plants already produce more energy than they need to operate from the biogas that forms during the breakdown of organic material.
Noguera said ten years from now the typical treatment plant would probably look pretty different from the one today. He also said that recovered resources might not only include clean water and energy, but also a variety of chemicals, such as fertilizers and precursors of plastics and fiber and as part of this evolution he believes anammox reactors will soon become conventional.