Scientists employ algae as biofuel, to mop up pollutants

SCIENTISTS have expanded the frontiers in the use of micro-organisms such as bacteria and algae for biofuel and in bioremediation with the utilization of wastewater algae.

Scientists, in one of the first studies to examine the potential for using municipal wastewater as a feedstock for algae-based biofuels, found they could grow high-value strains of oil-rich algae while simultaneously removing more than 90 percent of nitrates and more than 50 percent of phosphorous from wastewater.

A co-author of the study published in Algae said wastewater treatment facilities currently have no cost-effective means of removing large volumes of nitrates or phosphorus from treated water, so algae production with wastewater has the potential of solving two problems at once.

Rice University, United States, scientists found they could easily grow high-value strains of oil-rich algae while simultaneously removing more than 90 percent of nitrates and more than 50 percent of phosphorus from wastewater.

The findings, which are based on a five-month study at a wastewater treatment facility in Houston, United States, are available online in the journal Algae.

The study is titled “Low algal diversity systems are a promising method for biodiesel production in wastewater fed open reactors.”

According to Wikipedia, algae fuel or algal biofuel is an alternative to fossil fuel that uses algae as its source of natural deposits. Several companies and government agencies are funding efforts to reduce capital and operating costs and make algae fuel production commercially viable. Like fossil fuel, algae fuel releases carbondioxide (CO2) when burnt, but unlike fossil fuel, algae fuel and other biofuels only release CO2 recently removed from the atmosphere via photosynthesis as the algae or plant grew. The energy crisis and the world food crisis have ignited interest in algaculture (farming algae) for making biodiesel and other biofuels using land unsuitable for agriculture.

Several studies have shown that among algal fuels’ attractive characteristics are that they can be grown with minimal impact on fresh water resources, can be produced using saline and wastewater, have a high flash point, and are biodegradable and relatively harmless to the environment if spilled. Algae cost more per unit mass than other second-generation biofuel crops due to high capital and operating costs, but are claimed to yield between 10 and 100 times more fuel per unit area.

Recently, there has been increasing interest on using bacteria, fungi, plants and algae to remove, degrade, or render harmless organic pollutants in aquatic systems.

The algae play an important role in controlling and biomonitoring of organic pollutants in aquatic ecosystems. The use of higher plants and bacteria for bio-extraction and bioremediation of heavy metals and organic pollutants have been extensively studied.

A study published International Research Journal of Public and Environmental Health concluded: “From this review, we can conclude that the application of microalgae in biomoniroring and restoration of aquatic systems favour the phytoextraction and biodegradation of many organic pollutants; however there are still some persistent organic pollutants that are difficult to break down by the microalgae. The genetic engineering can solve this problem and offers a promising tool to improve the absorption and bioremediation of many organic pollutants and increase microalgal tolerance to these pollutants. It is also necessary to study and to control different parameters of aquatic ecosystems such as temperature, pH, nutrient availability and other environmental parameters to increase the absorption, accumulation and biodegradation of different pollutants by microalgae, thus accelerating the bioremediation process and reducing the time of decontamination of an aquatic ecosystem.”

Lead author of the Algae study Meenakshi Bhattacharjee, a 28-year veteran of algal research who joined Rice’s biosciences faculty in June, said: “Biofuels were the hot topic in algaculture five years ago, but interest cooled as the algae industry moved toward producing higher-value, lower-volume products for pharmaceuticals, nutritional supplements, cosmetics and other products.

“The move to high-value products has allowed the algaculture industry to become firmly established, but producers remain heavily dependent on chemical fertilizers. Moving forward, they must address sustainability if they are to progress toward producing higher-volume products, ‘green’ petrochemical substitutes and fuels.”

Bhattacharjee said the algae industry’s reliance on chemical fertilizers is a double whammy for algae producers because it both reduces profit margins and puts them in competition with food producers for fertilizers. A 2012 National Research Council report found that “with current technologies, scaling up production of algal biofuels to meet even five percent of U.S. transportation fuel needs could create unsustainable demands for energy, water and nutrient resources.”

The 2012 report also pointed to wastewater-based cultivation as a potential way to make algae production sustainable. An added appeal is that the method could potentially address a looming environmental problem: nutrient pollution in U.S. waterways. According to the Environmental Protection Agency, nutrient pollution from excess nitrogen and phosphorus — the two primary components of chemical fertilizers — is “one of America’s most widespread, costly and challenging environmental problems.”

Wastewater treatment facilities currently have no cost-effective means of removing large volumes of nitrates or phosphorus from treated water, so algae production with wastewater has the potential of solving two problems at once, said study co-author Evan Siemann, Rice’s Harry C. and Olga K. Wiess Professor of BioSciences.

“The idea has been on the books for quite a while, but there are questions, including whether it can be done in open tanks and whether it will be adaptable for monoculture — a preferred process where producers grow one algal strain that’s optimized to yield particular products,” he said. “We were surprised at how little had been done to test these questions. There are a number of laboratory studies, but we found only one previous large-scale study, which was conducted at a wastewater facility in Kansas.”

Siemann said the Rice study was made possible by the participation of the Houston Department of Public Works and Engineering, which helped Rice’s research team set up a test involving 12 open-topped 600-gallon tanks at one of the city’s satellite wastewater treatment plants in July 2013. The tanks were fed with filtered wastewater from the plant’s clarifiers, which remove suspended solids from sewage. Various formulations of algae were tested in each tank. Some were monocultures of oil-rich algal strains and others contained mixed cultures, including some with local algal strains from Houston bayous. Some tanks contained fish that preyed upon algae-eating zooplankton.

“Prior research had suggested that diverse assemblages of algal species might perform better in open tanks and that fish might keep algae-eating zooplankton from adversely affecting yields,” Siemann said.

“We recorded prolific algal growth in all 12 tanks,” he said. “Our results are likely to be very encouraging to algae producers because the case they would prefer — monocultures with no fish and no cross-contamination — was the case where we saw optimal performance.”

Bhattacharjee said more research is needed to determine whether wastewater-based algaculture will be cost-effective and under what circumstances.

For instance, the algae in the Rice study was four times more effective at removing phosphorus than were the algae in the Kansas study. She said that could be because the Houston test was performed in summer and fall, and the tanks were about 30 degrees warmer on average than the tanks in Kansas.

“Using wastewater would be one of the best solutions to make algaculture sustainable,” she said. “If temperature is key, then cultivation may be more economical in the Southeast and Southwest.” She noted that other factors, like starting levels of nitrogen and phosphorus, might have caused a rate-limiting effect. “These are the kinds of questions future studies would need to address to optimize this process and make it more attractive for investors,” she said.

Siemann said he hopes to partner with the city for future studies to further investigate the use of wastewater for algaculture.

“We are excited to be collaborating with Rice to develop innovative, sustainable approaches that remove excess nutrients from wastewater while producing algae-based biofuels, all to the benefit of Houston’s bayous,” said Carol La Breche, supervising engineering of wastewater operations at the Beltway Lab of the Houston Department of Public Works and Engineering.