A study by researchers in the biotechnology department at Rice University in Houston has found that growing single strains of oil-rich algae in wastewater could be “a viable production method to procure algal biomass for biodiesel production,” as well as a means of cleaning wastewater.
“Algae offer a tangible promise to fulfill the need for an alternative source of energy,” the researchers said. It can “produce a variety of high value compounds such as biodiesel and biofertilizer, without contributing to atmospheric carbon dioxide.”
In their study, “Low algal diversity systems are a promising method for biodiesel production in wastewater fed open reactors,” the researchers detailed their method of cultivating algae using wastewater as a medium.
They used 12 open-top plastic tanks, operated as continuous-flow reactors, to grow different lipid-rich algae and natural algal phytoplankton samples. They grew three strains of algae -- Spirulina platensis, Chlorella and Scenesdesmus obliques.
The method is less expensive than cultivating algal blooms in outdoor ponds, and has the added benefit of removing 90 percent of nitrates and more than 50 percent of phosphorus from the water, which in turn could “reduc[e] high nutrient loads in downstream watersheds,” they said.
At intervals of 15 days, the researchers sampled and measured variables including water quality and nutrient removal in the water being put into and being drained from tanks, and algal production as total suspended solids -- as well as factors such as dissolved oxygen, pH, temperature, and total dissolved solids.
They found that the tanks were “productive in terms of energy rich biomass suitable for biodiesel production, and “moreover, rates of nutrient removal were high.”
While it has previously been assumed that using diverse algal assemblages lead to more productive and more stable open reactors, the researchers found that their monocultures were stable, resistant to invasion and could produce "significant biomass."
They acknowledged that “the results of this pilot experiment are not equivalent to establishing long-term, large-scale, commercial efforts. However, they add to the set of demonstrations that algal biomass can be grown in open tank bioreactors using wastewater as a nutrient source for biodiesel production.”
In a recent interview with SciDev.Net, Meenakshi Banerjee Bhattacharjee, co-author of the study, said the method “would work very well in a country like India where the climate is suitable for algal growth and where there are many indigenous strains.”