As the World’s population increases so does the demand for Earth’s resources and the waste we produce. It is predicted that there will be excess of 9 billion people on the planet by mid-century, and some of the biggest future challenges include supplies of food, freshwater and a source of alternative and renewable energy. It is our actions today that will determine how successful we will be! More people means more wastewater; economic growth means more industrial effluents; and increasing agricultural productivity is in some part the consequence of enhanced fertiliser use. Ultimately, this leads to increased nutrients such as phosphorus and nitrogen in our water systems and it is here where the problems become more evident. Algae are feeding on the extra nutrients, and blooms are on the increase worldwide. They render water undrinkable, adversely impact fisheries and the tourism industry, damage the ecology and wildlife, and toxic blooms can also be a severe health hazard. Climate change exacerbates the problem by favouring the growth of algal blooms.
Current methods for remediation are not cost effective
Methods to remediate algal-bloom inflicted water systems include new policy and legislation on the control of nutrient run-off from industry, sewage and agriculture. However, the biotic and abiotic complexity of natural water systems means internal loading i.e. nutrients released from the sediment can delay rehabilitation for several decades. Similarly, efforts to lock nutrients in the sediment using alum are not perceived as a long-term solution. Bio-manipulation has had varied success, but controlling the outcome of introducing foreign species or augmenting with native species is very difficult and can generate new problems.
An attractive option is to remove the biomass. However, removing the biomass efficiently is a challenge. It would have to be concentrated before its removal and algal harvesting in the biofuel industry can be performed by sedimentation, dissolved air flotation (DAF), induced air flotation (IAF), membrane filtration and centrifugal dewatering. DAF is traditionally considered to be too costly for the scale that is required, until now.
Microbubble technology offers more cost effective solution
A low-pressure offset technique with the promise of cheap microbubble generation has been designed and is already being applied in various research sectors. Unlike conventional dispersed air mechanisms that depend to no avail on diffuser structure for the generation of microbubbles, fluidic oscillation pinches off the bubble at the infant stage. Microflotation (MF) is a flotation separation technique that entails the application of sub-100 µm sized bubbles generated by fluidic oscillation for the removal of colloidal particles; for example, algae cells from the liquid continuous phase. Essentially, it is a type of bubble column powered by the fluidic oscillator.
Traditional bubble based separation systems are expensive to operate simply because their mechanisms include additional operations with high energy demand such as in DAF and Induced Air Flotation (Jameson flotation cell for instance). Both techniques require pumping gas and liquid for bubble production. Given that the density difference between both fluids is approximately 1000-fold, pumping liquid consumes a 1000 times more energy than pumping gas. In microflotation, only gas is pumped, and microbubbles push just enough gas to displace water, so use only a thousandth the amount of energy. Essentially, you can get the same effect as in a standard DAF system, but save 90-95% of your capital and operating costs, as large saturators or pumps are not required.
Algae as a biofuel offers complementary revenue stream for cleaning up algal blooms
Although this breakthrough in biomass removal has the potential to vastly lower costs, the economic competiveness of these processes has historically slowed their progress with cultivation and harvesting costs simply too high. In remediation of lakes by recovery of algal biomass, this process cost is eliminated. The question becomes, is there a hidden economic incentive in cleaning up algal blooms? The secret to making biomass removal even more cost effective is to find complementary revenue streams within the process.
This could be especially rewarding as algae has been suggested as a possible source of bio-fuels. Algae store energy in the form of lipids, which can be readily converted to bio-diesel and jet fuel. Algal lipids are not just a source for fuel generation. Lipids can be used in cosmetic, pharmaceutical and nutraceutical manufacture. Algal protein can be used for animal feed or food supplements. The cellular carbohydrates can be converted to ethanol and methanol. The biomass can also be directly fed into anaerobic digesters to produce methane, which itself can be converted to heat and electricity. Phosphorous can also be retrieved for fertiliser, although, the biomass could directly be used and help to restore structure in eroded soils.
Professor Zimmerman is currently in discussions with officials in China to deliver CO2 flue gas through microbubbles, to help remove algae and hence, nutrients from a heavily polluted freshwater lake in Kunming Province. The main driver is to provide clean drinking water to the state; however, the costs for doing so are drastically reduced as the algae biomass can be sent to a processing plant to make value added commodities, e.g. fuel. Pilot-scale tests are required to model the process and aid prediction and controllability. Understanding the impact on biodiversity and ecosystem function would also be essential.
We are currently working with our partner AECOM to find other water related applications. However, China represents a possible major market for this new technology. The government has made tackling the drinking water supply problem, one of its main priorities. They have pledged to invest £400 billion to tackle predicted shortages, and provide support for the formation of 50 environmental protection service companies with revenues in excess of RMB1 billion. Considering over 40% of Chinese rivers are known to be badly polluted, this is not a trivial challenge. For more on this please see our review of the 2012 State of the Environment Report.
In an age when we are beginning to fully understand how crucial it is to protect the environment, combined with challenges to sustain the growing human population, innovative technology is required more than ever. Algal blooms are becoming more prevalent globally as a direct result of human waste and our carelessness. Preventative measures are paramount to avoid further ecological damage. However, the drivers for cleaning up algal blooms can often be economical and, therefore, fixing these broken ecosystems with financial incentives could assist in this principal goal.