Research Programmes
TKI-watertechnology programme
Phase 1 - Desk study
2015: Implementation of the Power-to-Protein concept in the Amsterdam urban water cycle.
Partners: Waternet, AEB Amsterdam, Avecom and KWR.
Objective: Research the technical and economic feasibility of the Power-to-Protein concept in the water cycle of the city of Amsterdam.
Status: Completed
Summary
In 2014-2015, a survey study was conducted in the framework of the TKI Water Technology programme to assess the feasibility of coupling the Power-to-Protein concept to the wastewater cycle, and to test it for the case of the ‘urban zone of Amsterdam’ (phase 1). The study showed the enormous potential of the concept, which could annually produce 6,300 tons of protein from the ammonium in the reject water of the sludge treatment at the Amsterdam West WWTP. This could satisfy the (net) protein requirements of 36% of the residents of Amsterdam. It also concluded that the production of single-cell protein () had economic potential, which moreover depends greatly on the production costs of the raw materials – ammonium and hydrogen – and on the market price of the end product.
On the basis of the phase 1 study, a number of recommendations were made which will be taken up in the phase 2 research:
- Closer research is needed into the risk that – in the case of the ammonium, carbon dioxide and hydrogen (via bio-methane) sources – undesirable substances, including organic micropollutants and pathogens, might be introduced to the SCP reactor. This research is crucial for the necessary reprocessing steps, and therefore constitutes an important factor in the SCP production costs.
- The recommendation was made to carry out a pilot research project in which the coupling to the wastewater cycle is done for only one of the raw materials, and to add the other raw materials in the form of high-grade industrial gases or products. This would provide insights into the effects on the microbiology and toxicology of the microbiome in the reactor. It is evident that this pilot work should initially concentrate on the ammonia/ammonium raw material.
- The process of bringing SCP to the market as a novel food should be clarified in more detail with regard to the timeframe and costs.
Phase 2 - Pilot research
2015/2016/2017/2018
Partners: Waternet, Waterkracht, AEB Amsterdam, Barentz Foods, Avecom, Allied Waters and KWR.
Technology supplier: Nijhuis Water Technology provides the pilot for ammonia recovery (NAR-pilot) that will produce the ammoniasulphate as input for the Power-to-Protein pilot
Objective: Scaling up the Power-to-Protein concept to the production level of 1 kg per day, in which a direct coupling is made to the wastewater cycle, followed by an assessment of the quality of the protein produced and of the concept’s economic and environmental benefits.
Status: Completed
Summary
The work on Power-to-Protein was continued in phase 2 by designing and building a pilot plant reactor with an intended production capacity of about 1 kg SCP per day. As hydrogen is the energy source of the HOB microbiome, special attention had to be paid to the design and construction of the pilot plant so that operational safety can be assured. The pilot plant was used to demonstrate the production of SCP and to monitor the production process at two STPs in The Netherlands.
To feed the power-to-protein pilot with recovered ammonia an existing pilot scale ammonia recovery system was used. This pilot plant (NAR-pilot, Nijhuis Water Technology) is based on air stripping at elevated temperatures and pH followed by absorption of the stripped ammonia in a sulphuric acid solution. On both locations, the reject water of the sludge digestion plants was used as source for the ammonia recovery step. This step is significant for the overall economics of the PtP-concept. The different steps within the NAR-pilot were closely monitored, particularly in terms of pathogens transfer from the reject water to the final ammonium sulphate solution produced. For this purpose challenge tests were performed with three indicator microorganisms to prove sufficient virus, bacteria and protozoa removal.
The biomass produced in the PtP-pilot was analysed for protein content, amino acids composition and in-vitro digestibility. The environmental impact of SCP was evaluated by performing a Life Cycle Analysis using SimaPro software and the EcoInvent 3.0 database.
Main conclusions
- Ammonia recovery using air stripping at elevated temperatures and pH turns out to be technically and economically feasible. The total costs of € 2.18 per kgN can be further reduced to € 1.54 per kgN when waste heat is available on location. Challenge test results show high removal efficiencies for indicator organisms (see table 1.1.) indicating that transfer of faecal pathogens from the reject water to the recovered ammonia sulphate is very unlikely.
- The quality of the produced SCP in the pilot reactor is compared to the product from the lab scale test. The crude protein content is lower (49 % and 75 % respectively) and so are the concentrations of essential amino acids. The in-vitro digestibility of the produced SCP is comparable to that of fishmeal.
- LCA results indicate that – due to the amount of electricity necessary for the hydrogen (and oxygen) production - the source of electricity is the determining factor in the case of environmental impact of SCP. So the “greener” the power source the lower the impact. In figure 1.2 a comparison is made between SCP and conventional protein sources per kg crude product for “off shore wind’ as a common power source in the future. With the interpretation of these data it is important to understand that the crude protein content of SCP is substantial higher than that of meat.
- Pilot results in general indicate insufficient hydrogen transfer efficiency in the pilot reactor resulting in direct loss of hydrogen and a relatively low specific SCP production capacity. Indirectly the low gas transfer of gasses in the reactor has had a negative influence on SCP-quality as well. So optimisation of the reactor concept in general and the hydrogen transfer in particular are crucial for the continuation of the PtP-concept.
Phase 3 - Efficient mass transfer of hydrogen in bioreactors
2019/2020
Partners: Avecom, Allied Water and KWR
Objective: The aim of this research is to gain more insight into the substance transfer of hydrogen and other gases in bioreactors through literature study, modelling and bench-scale testing so that proteins from ammonium - originating from wastewater - can be produced.
Status: Completed
Summary
As phase 2 showed that optimisation of the reactor concept in general and the hydrogen transfer, in particular, are crucial, in this phase 3 study more insight was gained with regard to the mass transfer of hydrogen in bioreactors. The analysis in this study, based on literature review, knowledge exchange with experts and a modelling study targeted bubble column reactors in particular.
From the literature review conducted, it was established that bubble column and slurry bubble column reactors are suitable reactor types or configurations to achieve high performance in gas-to-liquid mass transfer and better gas hold-up. Such a conclusion was confirmed by experts who were consulted in a knowledge exchange meeting. Additionally, key design and operating parameters were also identified from literature and expert consultation to develop a CFD model that simulated the performance of the bubble column reactor under varying design and operating conditions. From the modelling study, it was concluded that the most important parameters to be considered with respect to improving performance were bubble size, pressure and aspect ratio. These key findings from the study supported the methodology followed by Avecom, providing additional confidence to Avecom and the project partners on the pilot-scale bubble column reactor currently in operation. Recommendations were also provided in what parameter values can be considered for the design and operations of a larger scale reactor, as envisioned to be pursued by Avecom and its project partners. Additionally, key recommendations regarding the monitoring of the operating parameters through the deployment of sensors were provided. With the availability of additional data, further calibration and validation of the current CFD model can be conducted to increase its prediction accuracy.
Main conclusions
- The bubble column or slurry bubble column reactors are preferred reactor configurations to achieve a high performance of gas-to-liquid mass transfer. Furthermore, specific to the mass transfer of hydrogen, bubble column reactors are more suitable.
- Key design and operating parameters have been identified from the literature and expert consultations for the development of the CFD model to simulate the performance of the bubble column reactor.
- From the modelling exercise and sensitivity analysis, it was concluded that the most important parameters to improve reactor performance are bubble size, pressure and aspect ratio. The aspect ratio is already close to the optimal value (~18) in the model, whereas increasing pressure and decreasing bubble size (<0.9mm) could lead to a better reactor performance. For instance, increasing the pressure from 1.3bar to 5 bars gives a yield 3 times faster.
- The preliminary stage of model development and simulations has offered key insights into the power-to-protein process in a bubble column bioreactor. Obtaining additional operating and monitoring data from the current pilot plant or a scale-up plant will assist in optimising the above key parameters both by improving the bioreactor design and operation as well as further calibrating and validating the CFD model developed.
The Wetsus programme
Parallel with TKI Water Technology
In parallel with the TKI Water Technology project, Wetsus conducts research into the development of the microbiome in the Power-to-Protein reactor, with a focus on safeguarding the growth process. A second Wetsus project concentrates on the process aspects, particularly on the development, over the long term, of an alternative to the air stripping of NH3 – for example, ammonia stripping through membrane electrolysis.
Partners: Avecom, DC Water (Washington, DC), University of Ghent
Status: First PhD project started in March '16, second PhD project is still to start.
Contact: Raquel Barbosa MSc., Dr.ir. Tom Sleutels
Summary
The aim of the first PhD project at Wetsus, executed by Raquel Barbosa with supervision of Prof.dr.ir. Nico Boon from UGhent, is to compose in vitro synthetic hydrogen oxidising multispecies communities/collaboromes (HOC) consisting of hydrogen oxidising bacteria as core populations and heterotrophic bacteria as satellites, that are selected towards interesting biotechnological endpoints, such as single cell protein, polyunsaturated fatty acids, polyhydroxybuteric acid, vitamins, amino acids and biopolymers, and to elucidate the crucial members and interaction mechanisms.
Initially, isolation will be used to dissect a mixed microbial community (enrichment of original sample) into culture collections of heterotrophs and hydrogen oxidising bacteria. Subsequently, different sets of isolates will be assembled and the best performing HOC will be selected by evaluating the performance (specific metabolite production) of the HOC in high-throughput essays.