The addition of algae to a wastewater bioreactor has improved the treatment process to the point that it exceeds the efficacy of standard municipal water treatment methods, according to new research from Drexel University.
A team of university environmental engineers created a high-density bioreactor system able to remove several compounds from wastewater simultaneously. The system, based on activated sludge systems, adds algae for improved nitrogen removal. The algae are able to remove up to 80 percent of nitrogen from wastewater, according to researchers.
Christopher Sales, an assistant professor in the College of Engineering, originally developed the system in 2006 with a colleague from the University of Pennsylvania.
The cultivated algae biomass could be easily recovered in this system, making it a potentially valuable source of large quantities of the substance for biodiesel production.
Nutrients in Water Supplies
Algae can help prevent excess nutrients from entering local water supplies, which has been a problem for some communities. Sales explains:
One of the most time-consuming and expensive components to wastewater treatment today is ridding water of nutrients such as nitrogen and phosphorus, which often make their way into water from our household toilets and sinks. […] The release of excess nitrogen species into a water supply can lead to accelerated growth of cyanobacteria and algae — and create a massive algal bloom like the one in Lake Erie last summer which caused the contamination of the entire water supply of Toledo, Ohio.
Conventional nitrogen-removal techniques require several steps — such as nitrification and denitrification — as well as time-consuming settling. Additionally, chemicals such as methanol may be needed in these systems, which also require significant energy to operate.
System Being Tested
This new bioreactor continuously cycles water into an algae and bacteria-laden environment. The nitrogen is removed by the algae that store it. The algae can be easily separated from water without requiring a separate settling tank as the bioreactor’s design naturally promotes settling.
The system, which is still under development, is being bench-tested in a prototype setup that consists of a 1-liter graduated cylinder filled with an algae-liquid mixture. A water jug of synthetic wastewater — which, like conventional wastewater, is full of ammonia and nitrate — enters the system through a pump and beaker, then passes through the flask containing algae and some 350 species of microbes. These microbes either metabolize ammonia to nitrate or convert the dead algal cells into carbon dioxide. The algae are able to grow and their photosynthesis produces oxygen that helps the bacteria thrive. The treated effluent is ejected into a bucket.
Jacob Price, a doctoral researcher in the Sales lab, explains:
Our wastewater is actually the perfect environment for algae and bacteria to thrive in a symbiotic circle of life. […] Plants use [nitrate], along with carbon dioxide and light […] to fuel growth. A byproduct of photosynthesis is oxygen, which is used by organisms — like bacteria — for their commensurate life processes. It’s a beautifully natural relationship that we can harness to clean our water.
A previous Drexel University project, funded by the United States Environmental Protection Agency, similarly looked at using an algae bioreactor to treat landfill leachate, the wastewater occurring in dumps. The work included an economic analysis of the potential for a specific landfill site in Delaware to recoup its expenses through the sale of algae byproducts, such as lipids and other chemicals used in cosmetics and pharmaceuticals, and as a biofuel feedstock. In October 2015, Drexel University student Kaitie Sniffen provided an update on the work to Waste 360, stating that more research is needed on this particular application of algae to wastewater treatment.
As Duke University student Sarah Loftus explained in a 2013 blog post on the Nicholas School of the Environment website:
Growing algae on wastewater is an old concept, but the process of using wastewater as a water and nutrient source for growing algae for biofuels is relatively younger.
By using wastewater from various sources for large-scale algae growth operations, both the algal biofuels industry and wastewater treatment would reap benefits.
The latest Drexel University research findings — “A Novel Bioreactor for High Density Cultivation of Diverse Microbial Communities” — have been published in the Journal of Visualized Experiments.