It’s All About the Critters: Who Can Remove Nitrogen from Dairy Waste?
Posted by embrey.bronstad | November 12, 2020
This is part of a series of posts highlighting work by Washington State University researchers through the Applied Bioenergy Research Program of the Agricultural Research Center at Washington State University, College of Agricultural, Human, and Natural Resource Sciences.
Here is an ammonia joke for you: Why do chemistry students like studying ammonia? Because it’s pretty basic stuff!
So basic, in fact, that high levels of ammonia in dairy wastewater inhibit algal growth. For researchers at WSU looking to use algae as a natural way to extract high levels of nitrogen from dairy waste, this posed a problem. Fortunately, an intrepid graduate student made a breakthrough. And that’s not another chemistry joke.
Algae take up nitrogen and phosphorus to support their growth, which also means that these nutrients are removed from the water in which algae are growing. In uncontrolled systems (the Gulf of Mexico’s hypoxic zone, for example), the nutrient consumption and resulting runaway algal bloom is an environmental catastrophe. But what if this biological process could be harnessed in engineered systems to remove nitrogen from wastewater naturally, in lieu of expensive, energy intensive physical or chemical treatments? Not only can algae take up significant quantities of these nutrients, but the resulting algal biomass can also be used as animal feed or feedstock for biofuel production. It is a potential win-win.
While algal bioreactors fed by municipal wastewater effluent have been employed around the world both as polishing steps to remove nitrogen and phosphorus and in algae farms for supporting algal biomass growth, there have been impediments to using dairy wastewater in these types of installations. One of those impediments is that dairy waste contains significant concentrations of nitrogen as ammonia, which is a form of nitrogen toxic to algae at high levels. Another not inconsequential characteristic of dairy wastewater is its high turbidity, which makes sunlight penetration and therefore algal photosynthesis and growth very difficult. Without some form of dairy wastewater pretreatment that would reduce ammonia and turbidity, these were ostensible deal breakers for algal nutrient removal… unless a strain of algae with a robust tolerance to ammonia that could grow in high turbidity conditions could be isolated and cultivated to densities capable of treating dairy waste.
Andre Bergeron, a PhD candidate working with Dr. Shulin Chen in the Department of Biological Systems Engineering, decided he just had to give it a try. Andre took myriad water samples around a Washington state dairy, dipping into the wastewater lagoons to find algae as well as taking contemporaneous ammonia and pH values from each of his sampling points. The day was cold, the lagoons were murky, but he persisted.
Much to the excitement of the research team, Andre and another of Dr. Chen’s students, Na Pang, isolated a strain of Chlorella vulgaris algae from samples taken from these dairy lagoons, lagoons that were not only cold and highly turbid, but that contained a whopping 2 g/L of ammonia. By contrast, raw municipal wastewater contains ammonia concentrations around 30-50 mg/L. To the best of the team’s knowledge, this is the highest recorded ammonia environment from which an alga has been isolated.
What does this mean for sustainable agriculture? First and foremost, it is a step towards potentially closing a significant on-farm nutrient loop by using a naturally occurring process—algal growth—to reduce a possible environmental liability—dairy wastewater rich in nitrogen and phosphorus. Growing algae using dairy wastewater not only diminishes the nutrient load of the waste but provides a saleable product in the form of animal feed, so the algal biomass can also be used to offset the feed inputs to the farm. Unlike physical and chemical processes that may require hazardous solvents, polymers, and other energy inputs, a low-energy, technically simple system with algae at its core meets environmental and economic metrics without placing undue burden on the farmer. Isolating this alga is the first key step. Stay tuned for more as WSU investigates the optimization and scale-up potential of algal nutrient removal treatment processes, as well as how they integrate into productive and sustainable food-energy-water nexus systems.