Maximizing profits in residual streams: from waste to value

Lars Angenent, Professor in Biological and Environmental Engineering at Cornell University, in the USA, pleads for a multi-disciplinary approach within environmental sciences. ‘We should connect different disciplines within the field to achieve more efficient production and extraction of valuable substances from waste’, he says. ‘At the same time, we should aim for maximizing returns.’

Angenent graduated for his M.Sc. at ETE in the nineties and moved to the USA where he completed his Ph.D. at Iowa State University in anaerobic wastewater treatment. In 2008 he moved to Cornell University as an associate professor, where he currently has a full professor position. He is focusing his research on the production of valuable compounds from waste.  According to him, the Netherlands are an example for the USA in the way the Dutch treat waste: recovery and reuse of valuable compounds is already more common and more sophisticated. During the last decades, some crucial technologies with lasting impacts on the field of environmental technology were designed by ETE. ‘A breakthrough was undoubtedly the ´Upflow Anaerobic Sludge Blanket´ (UASB) reactor, invented by former ETE professor Gatze Lettinga. But also the Thiopaques, developed by ETE professor Cees Buisman and Paques BV, had a major impact’, Angenent states. In the UASB concept, microorganisms digest wastewater using anaerobic fermentation. The technology has been spread around the world, resulting in the education of many people in wastewater cleaning. The Thiopaques adds an important step to the UASB reactor by recovering sulfur from anaerobically digested wastewater, a valuable raw material. A more recent ETE breakthrough-development, discovered by Kirsten Steinbusch, a Ph.D. scientist of ETE, is the production of the substance caproate by chain elongation. This valuable molecule is formed by microorganisms from organic waste and can be upgraded to chemicals. ‘This technology is going to considerably change the field again‘, Angenent says.


Maximizing profit
According to Angenent, a key to advance the field even more is to see waste as a source of, for example, future chemical production. Scientists in environmental technology can learn a lot from multinationals. For example, oil companies process their crude oil in a way that is commercially most beneficial. ‘Like Shell, we should aim for the highest returns from processing waste’, Angenent says. ‘We should recover as many compounds as possible, reuse them in economically best ways, while maximizing profit.’ For example, wastewater should not only be purified, but the remaining nutrients should be recovered and reused as well. The best way to achieve this is to combine the use of different technologies. This methodology is still in its infancy, but at ETE some initial steps have been made: the recovery of nitrogen and phosphorous as struvite, using a simple precipitation reaction. Struvite crystals should be further purified and processed to increase their application and value, Angenent thinks. Also the formation of phosphorous granules during anaerobic digestion of wastewater, discovered by Taina Tervahauta, a Ph.D. scientist of ETE, is a promising discovery that should be developed further. Angenent: ´In this particular example it is important to think about creating the highest value from these granules. For example, microorganisms could be grown on CO2 from biogas and use these phosphorous granules and nitrogen from another recovery technology as a feed source. The microorganisms could subsequently be dried and added to animal feed.’ 

Easier extraction
In line with his views, Angenent’s main long-term research goal is to utilize products resulting from waste treatment as efficient as possible, while maximizing their value. To achieve this, his research focuses on the development of extraction and biorefinery technologies to produce useful compounds from waste streams. To facilitate extraction, an important strategy is to use microorganisms to increase the molecular size of useful end products, because the bigger the molecule, the easier it is to separate and extract it. ‘For example, microorganisms convert complex organic wastes into acetate and butyrate, small molecules with a carbon chain of only 2 and 4 C-atoms’, Angenent explains. ‘Adding ethanol to the reaction mixture results in the microbiological elongation of these small molecules into bigger molecules with 6 and 8 C-atoms.’ In several steps, microbiota convert acetate eventually into caproate. This larger, valuable, molecule can be used as a ‘platform chemical’ to make many products, including biofuels. It can be extracted from the microorganisms by integration with an extraction technology that was recently performed by Angenent’s research group. Angenent: ‘In this research we have combined knowledge about microbiological conversions, with extraction and biorefinery technologies, resulting in a higher value product.’