Can MicroNiche Engineering help close the phosphorus loop?

     According to the Cambridge Dictionary, the definition of the idiom to “reinvent the wheel” is “to waste time trying to create something that someone else has already created.” The wheel is an ancient tool and facilitates the movement of heavy loads. And, it’s very much taken for granted in our modern world.

     But, as you probably guessed by title of this article, I am not here to talk about the wheel.

     I can’t help but notice the similarities between our contemporary treatment of the wheel—a well-established but under-appreciated piece of technology—and an even more ancient and circular process: the nutrient cycles.

     Nutrient cycles are the collections of pathways, organic and inorganic, through which crucial elements, such as carbon, nitrogen, and phosphorus travel in the environment. As nutrient loops are subject to human interference, our mis-management of nutrients can cause devastating effects to both the planet and its inhabitants. Think of global warming as human emissions of carbon outstrip the environment’s ability to sequester it, or increasingly common “dead zones” and eutrophication as waterways are overwhelmed by the addition of nitrogen and phosphorus from agricultural and industrial sources.

     Phosphorus is one of the critical nutrients that loops its way through our environment. The cycle starts with phosphorus-containing minerals weathering and releasing phosphate into the environment. These ions find their way into water and soil and are consumed by plants. The plants are then consumed by animals, which through their excrement and eventual decomposition, return the phosphorus to soils and waters. Bacteria also play a role in the loop, mineralizing organic phosphorus into bio-available phosphate ions. Over the course of millions of years, phosphorus in ocean sediments will be converted back to the phosphorus-containing minerals that will begin the cycle anew.

     Because phosphate is critical for plant growth, mineral deposits of phosphorus are heavily mined to provide fertilizer. These deposits cannot be replaced on a human timescale; when withdrawals outpace deposits, we will run out of phosphorus. Some people have referred to this tipping point as “peak phosphorus.”

     While we mine phosphorus to introduce it into the environment, we must also strive to remove it from our wastewater and prevent it from persisting in our waterways. In the U.S. EPA’s report entitled “A Compilation of Cost Data Associated with the Impacts and Control of Nutrient Pollution”, it’s established that high nutrient discharge can lead to financial losses for the tourism and fishing industries, increased operating costs for drinking water facilities, increased spending on environmental mitigation, declining property values, and increased healthcare costs. The losses and spending increases range from hundreds of thousands of dollars to millions of dollars a year, depending on the area of the country and the market examined.

     To help combat these effects, effluent discharge limits for some areas in the United States could be as low as 0.1 mg P/L total phosphorus by 2025. This presents us with two key questions tied together by the nutrient cycle: How do we meet these standards to protect ourselves and our aquatic environments and where can we find more phosphorus?

     One elegant answer to both these questions is enhanced biological phosphorus removal (EBPR), a process by which a group of bacteria known as poly-phosphate accumulating organisms (PAOs) take up and store phosphate beyond what is needed for cellular processes. This process is known as “luxury uptake” and occurs under aerobic conditions. For wastewater treatment plants that use EBPR in their treatment trains, this is where the story ends. The sludge containing the phosphorus-rich cells is wasted and shipped to landfills or used as a fertilizer (though its application there is often limited by the amount of nitrogen present in the sludge). Furthermore, it is estimated that 40% of a WWTP’s yearly operating cost are incurred for this solids management.

     As with many traditional biological systems, EBPR can be temperamental and very stringent discharge limits are challenging for these systems to achieve. On the other hand, chemical precipitation, where iron or aluminum may be used to knock phosphate out of solution, is quite predictable. But due to the increase in chemicals needed to reduce the effluent concentration to meet more stringent limits, costs for this reliable method will inevitably increase. Additionally, chemical processes leave the phosphate unavailable for use as a fertilizer and, as with the sludge produced from EBPR activated sludge plants, this incurs solid waste costs for handling and disposal. A Water Environmental Federation (WEF) study estimated that only 21% of all phosphorus passing through water resource recovery facilities in the United States is recovered and, of that, only 1% is recovered as a resource stream. The bottom line is that we will need technologies to recover more of this waste to close this ever-widening gap in the global phosphorus loop.

     This is where Microvi’s MicroNiche Engineering™ (MNE) platform comes in. The MNE platform is used by Microvi to create biocatalytic composites based on advanced materials science harnessing the most effective, naturally occurring microorganisms for a given process. MNE provides these organisms the optimum environment for them to flourish and deliver the desired treatment outcomes. Unlike other biological systems, MNE does not rely on organism growth within a bioreactor to maintain the population density.

     Where traditional EBPR’s story ends, MNE’s story begins. Once PAOs store orthophosphate in their cells aerobically, these organisms can then release the orthophosphate back into the environment under anaerobic conditions in the presence of a carbon source. While this may seem counterintuitive from a removal stand-point, Microvi’s EBPR bench and pilot studies, conducted with biocatalysts housing microbes harvested directly from an operating EBPR activated sludge plant, demonstrated that this anaerobic phase can provide a nutrient stream, which could be used for fertilizer production, in addition to the stream of treated water.

     Over the course of approximately four months, bench-scale studies using MNE EBPR biocatalysts in a sequencing batch reactor (SBR) alternating between aerobic and anaerobic conditions showed an average aerobic effluent orthophosphate concentration of less than 0.1 mg-P/L. This represented 99% orthophosphate removal from the influent, with concentrations ranging from 5 to 10 mg-P/L. Up to 70% of the orthophosphate removed and stored in the PAOs over the aerobic conditions was observed to be released over the anaerobic conditions.

     Similar results were noted in a pilot system over a month and a half of operation. Additional bench studies demonstrated that the MNE system is capable of near-complete removal of orthophosphate spikes of over 70 mg-P/L. It was also observed that the MNE system produces minimal solids (less than 200 mg/L generally) and shows rapid performance recovery following system upset. Both of these are advantageous over traditional activated sludge EBPR. Finally, metagenomic analysis of biocatalysts samples collected over the course of the bench and pilot studies demonstrated the MNE technology’s ability to retain organisms suspected to be PAOs responsible for EBPR in working wastewater systems, including bacteria in the Rhodocyclaceae and Comamonadaceae families. The application of MNE in this case in particularly innovative, given its ability to house an entire functioning EBPR community over a long period of time.

     Through these studies we have shown that, with the help of MNE’s material science innovations specially designed to retain, protect, and assist active naturally-occurring microbes, EBPR may help us close the gap in the phosphorus loop created by human activity. We can protect our waterways through the removal of phosphate and provide phosphate for fertilizer without further depletion of our phosphorus deposits.

     Let’s harness the process we already have waiting at our fingertips, performed by ancient organisms already present in our environment.

     Let’s close the loop without reinventing the wheel.

Acknowledgments:

Work described in this story was funded under EPA projects EPD17007 and EPD18008 and has been published in Bioresource Technology Reports under the title "High-performing enhanced biological phosphorus removal (EBPR) utilizing controlled communities of bacteria in novel biocatalyst composites". We would also like to acknowledge the support of Jason Warner and Jimmy Dang at Oro Loma Sanitary District for providing wastewater for our studies and hosting our demonstration plant.