The TKI Water Technology Power-to-Protein project involves the fixation of ammonium and carbon dioxide in the form of single-cell protein by hydrogen-oxidising bacteria. These bacteria are located in a reactor that is fed with raw materials from the wastewater cycle. Following a laboratory test-phase, the pilot-scale reactor was developed by KWR and Avecom. The reactor has been set up at the Enschede WWTP of the Vechtstromen Waterboard and, in four months’ time, will be moved to Waternet’s WWTP at Horstermeer.
Special reactor design
The reactor is fed with hydrogen (as the energy carrier) and oxygen (to feed the bacteria) from an electrolysis cell, carbon dioxide from gas cylinders, and ammonium from wastewater. The conversion in the reactor is very efficient: up to 70% of the dry-cell weight consists of the protein to be harvested. The project required close attention to the reactor design. The challenge was to produce an inherently safe design, that is: no hydrogen accumulation, while making maximum possible use of the oxygen. Besides this safety aspect, other central issues were the scaling-up of the reactor, a concept with continuous operational management, and an effective substance transfer . A patent request has been submitted for the reactor design.
Demonstration at two sites
The research focuses primarily on the operation of the concept and the analysis of the purity and nutritional value of the protein produced. In the period ahead, the pilot will be tested first at Vechtstromen Waterboard’s Enschede WWTP and then at Waternet’s Horstermeer WWTP. At both sites the connection will be made with the wastewater cycle through the use of ammonium sulphate as feedstock. This ammonium sulphate is produced using the Nijhuis Ammonia Recovery (NAR) pilot of the Nijhuis Water Technology company. The NAR pilot operates on the basis of air stripping at elevated temperatures, and is fed with centrate from the reject water which is rich in ammonium.
Nomination for the Enlightenmentz Process award
In 2017, Power-to-Protein was nominated for the Enlightenmentz Process award.