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Algae, 'electric' bacteria could help treat wastewater

Photo submitted by University of Arkansas. UArk algae wastewater.jpg
Chlorella vulgaris algae grown in waste water.
Freshwater algae removes pollutants from wastewater, while electroactive bacteria may improve traditional wastewater filter systems.

A pair of unrelated studies could provide new tools for treating liquid waste products from animal agriculture, even though both projects were developed for municipal wastewater treatment.

In the first study, led by the University of Arkansas, environmental engineers discovered that Chlorella vulgaris, a single-celled freshwater algae species, effectively removes pollutants from wastewater even at fluctuating levels, making it an effective tool for wastewater treatment.

The study, published recently in Water Environment Research, indicates that C. vulgaris continues to remove harmful elements like nitrogen and phosphorous from wastewater even after one type of pollutant is depleted, the university said. Some algae require both nitrogen and phosphorous to be present to function, which can limit its effectiveness in wastewater treatment.

“One of the factors that significantly impacts algal wastewater treatment is nutrient availability,” said Wen Zhang, associate professor in the University of Arkansas department of civil engineering. “What is the ideal range of nitrogen-to-phosphorous mass ratio for algal growth? Because previous research failed to identify this, the efficacy of algal treatment has been difficult to predict or optimize.”

Wastewater quality fluctuates dramatically, which makes it difficult to initiate and maintain algae growth for treatment, the university said, pointing out that Zhang’s study shows that C. vulgaris could survive even in the absence of either nutrient.

Zhang worked with John Chamberlin, doctoral student in the environmental dynamics program, and Kristen Harrison, an undergraduate honors student in the department of crop, soil and environmental sciences at the university.

The researchers said they grew the algae in synthetic wastewater under several nutrient-limiting conditions and in effluent from two wastewater treatment plants. They found that C. vulgaris removed both nitrogen and phosphorous after secondary wastewater treatment in all levels or ratios of nutrients tested.

'Electric' bacteria

In another study, European researchers developed a full-scale application of an eco-friendly technology that treats sewage water with zero energy costs.

“In 2010, when I discovered the beauty of constructed wetlands, I decided to apply my knowledge on microbial electrochemical technologies,” explained professor Abraham Esteve-Núñez from the University of Alcalá in Madrid, Spain. He improved traditional filter systems using conductive material to fill the wetlands. This acts as physical supports for bacteria that produce electricity when breaking down organic waste.

“Combining electroactive bacteria with electroconductive material has resulted in depuration rates that are 10 times higher than with traditional techniques,” Arantxa Aguirre from the Foundation Center for New Water Technologies in Spain explained of the research. “We also planted Cyperus papyrusand Iris pseudacorus. These plants help to remove nitrogen and phosphorus, and their main effect is the aeration of the bed, because the oxygen goes through the plants in the bed of the tank.”

Moreover, the system avoids clogging the biofilters with sediment, and the result is very low biomass. The bacteria remove pollutants from the wastewater, and after electro-oxidative treatment, the process produces water that is free of pathogens and suitable for irrigation, according to the post on youris, a European research media center.

The system can clean up to 25,000 liters of water per day.

According to the announcement, what makes the technology especially innovative is the way the electroactive bacteria’s metabolism converts pollution into electricity: The more the bacteria eat, the more electricity is harvested.

“One of the challenges of the project was coping with real conditions such as unexpected seasonal changes, so we tested our open-field wetland in different climates in Europe, from the hot Mediterranean summer of Spain to the freezing winter of Denmark,” Esteve-Núñez said.

The technology was met with success in the village of Ørby, northeast of Haderslev, Denmark, by Aarhus University.

The researchers said the concept is being currently tested in Argentina and Mexico, but the technology has already passed both research and pilot-scale tests and is ready for an attempt at a full-scale demonstration.

“We set up a spin-off company, METfilter, owned by the same researchers of the project, so we have now a further instrument to enter the market,” Esteve-Núñez said.

The company also joined another project called ELECTRA (which stands for electricity-driven low-energy and chemical input technology for accelerated bioremediation) that aims to improve bioremediation of groundwater, wastewater as well as sediment and soil. It comprises a consortium of 17 universities, research centers and companies in the European Union and China that work together to implement the technology.

“We will treat not only domestic sewage but also industrial wastewater. Instead of sending it to general municipality water treatment, companies will have a sustainable tool to treat it on site and reuse the clean water for their own purpose,” Esteve-Núñez concluded.

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