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Novel monitoring and process control system <br/>for efficient production of VFA and biogas in anaerobic digestion plant

Final Report Summary - OPTI-VFA (Novel monitoring and process control system <br/>for efficient production of VFA and biogas in anaerobic digestion plant)

Executive Summary:
OPTI-VFA was a two year applied research project, which commenced in September 2013 and finished in August 2015, and was funded under the “Research for SMEs” programme of the European Commission’s Seventh Framework Programme (FP7).
The project aimed to develop an OPTI-VFA pre-commercial prototype based on Fabry-Perot based spectrometer together with the ATR probe and an automatic control solution that provides real-time measurements of volatile fatty acid (VFA) profiles from the anaerobic digestion (AD) process as well as a more efficient process control tool. This system enables more efficient control of both volatile fatty acids and biogas production. The project outputs represent a breakthrough in terms of improved understanding and ability to control the complex AD process. A successful OPTI-VFA tool for measuring the total VFA amount as well as a number of critical VFAs during the AD process, involving no sampling and providing the results in real-time would offer significant strategic benefits to the SMEs within the consortium, once the results become available in the marketplace.

Project Context and Objectives:
OPTI-VFA was a two year applied research project, which commenced in September 2013 and finished in August 2015, and was funded under the “Research for SMEs” programme of the European Commission’s Seventh Framework Programme (FP7).
The number of operating agricultural anaerobic digestion (AD) plants has remained insupportable low, despite the numerous environmental advantages of AD process. The main challenges in the traditional biogas production are high investment costs of digesters, low profitability of biogas and energy production as well as the stability problems of operation especially in co-digestion plants. In this process scheme, the more efficient process control provides an approach to reduce the size and price of newly-built digesters, or to improve the performance and profitability of existing AD plants.
Another possibility is to switch from biogas production to VFA recovery in agroindustrial anaerobic digesters by means of OPTI-VFA on-line monitoring. Although thousands of anaerobic digesters located all over the EU have been running for years with the aim of producing methane-rich biogas, the economic feasibility of an important number of existing facilities may be seriously threatened by the new national legislation related to renewable energy. As most other commodity chemicals, VFA are currently being produced from fossil fuels through chemical synthesis, so there is a potential to shift AD by-products from simple intermediates to valuable end-products, thus reducing the dependency of the chemical industry sector on non-renewable fossil fuels. Cost-effective production of VFA will create new markets by providing novel opportunities for the chemical industry.
To this end, OPTI-VFA project aimed to develop an affordable, reliable on-line tool for the rapid monitoring of VFA profiles and an automatic control solution for the anaerobic digestion (AD) process. The OPTI-VFA measurement system consists of a spectrometer, ATR probe and chemometric models for VFAs. A commercial FT-IR and the built Fabry-Perot based prototype were used as a spectrometer in the project. Gas chromatography of VFA analysis was also chosen as the reference measurement for the development and validation of the calibration models of the OPTIVFA measurement systems. Chemometric models were developed to predict VFA concentrations based on FT-IR/ATR spectral data. The biowaste containing garden waste and kitchen waste from households was employed as substrate for a 2-phase conventional anaerobic digestion system to examine the optimization of biogas production, the validation of the performance of the OPTIVFA measurement system and the validation of the control strategy. The developed OPTI-VFA measurement system was also validated in a full scale biogas plant. As opposed to existing reference analytical methods, OPTI-VFA requires no sample preparation and provides the results in real-time. An OPTI-VFA prototype for measuring specific VFAs was developed, built and successfully tested in a laboratory scale.

Project Results:
The first phase of the project focused on defining the technological needs and aspirations of end users, as well as the expectations of the SMEs within the consortium, and both the industry and research partners worked closely together to define the industrial specifications. The most important parameters to monitor and control during the AD process were defined.
The literature reports indicate that AD reactors in most biogas plants were operated under suboptimal condition to avoid process failure. The results of the questionnaire survey, the on-site visits of biogas plants, and reviewing the literature reports and patents all indicated that there is a need of a cost-effective and user-friendly online VFA monitoring system, which would be very beneficial in the improvement of the performance of AD digesters for either biogas production and/or VFA production and the enhancement of the capacity of the plants.
Following the definition of system specification, laboratory research conducted in WP 1 and 2 evaluated the performance of the proposed FT-IR/ATR technology for the measurement of different VFAs.
A feasibility study was performed at laboratory scale with several experimental set-ups. Spectral measurements were carried out on purposely-prepared model compound solutions, as well as on real AD samples. Calibration of the FT-IR instrument was carried out with calibration samples prepared according to a statistically sound orthogonal mixture design based on spiked samples extracted from an industrial AD process. Two novel spectroscopic calibration methodologies, namely the science-based calibration (SBC), and a parsimonious model based on absorbance values from only four wavelengths channels, were tested and their performances were compared to that of the standard partial least squares (PLS) regression methodology. Based on assessment on an independent test set and on process data, both novel methods proved to be equivalent with PLS in the quantification of the total VFA level, and, with the added simplicity and robustness, they were demonstrated to be strong candidates for use in the calibration of a VFA sensor based on infrared spectroscopy.
Optical, electrical, mechanical and software design and manufacturing of the OPTI-VFA pre-competitive prototype have been completed. The specifications for the piezo actuated Fabry-Perot Interferometer (PFPI) mirrors were prepared based on simulations and instrument requirements. The built prototype is essentially a fiber optic mid-infrared spectrometer, which comprises two arms equipped with Fabry-Perot interferometers and detectors. The prototype wavelength calibration and performance tests have been carried out for both PFPI arms. The prototype could reliably measure typical VFAs.
A general simulation-based methodology has been developed to design and validate automatic controllers for conventional Anaerobic Digesters. Using this methodology, a probing control strategy has been designed to diagnose the status of the AD reactor and, based on that, automatically drive the process to its maximum treatment capacity in spite of external disturbances. The probing control strategy has been satisfactorily validated in a lab-scale AD reactor. Similarly, a simulation-based procedure has been developed to concurrently deal with the dimensioning of the plant components (tanks, reactor, gas holder) and the design of the control solution.
The prototype was demonstrated internally to the consortium members at different stages of development. The OPTI-VFA system was also demonstrated for wider audience. The validation of the OPTI-VFA system for monitoring VFAs under high VFA and low VFA conditions took place at the facilities of the project’s industrial partner ATTERO in the Netherlands during 2015. The performance of the control strategy was demonstrated and validated in the laboratory scale 2-phase system. The online VFA monitoring system was capable of detecting accurately the dynamic profile of some VFAs species (acetic and propionic acid) and total VFA in the AD process, and would be very conducive to steering VFA production in AD processes and obtaining the desired VFA spectra. OPTI-VFA system was also able to quantify the concentrations of ammonia and bicarbonate in the liquid, which are also important indication parameters in anaerobic digestion processes.
Given that this project delivered a pre-competitive prototype system, post project development work would be needed to industrialise the precompetitive output to a commercial system that is market exploitable. The Consortium is confident that there is potential for developing an affordable instrument for quantifying VFAs, ammonia and bicarbonate as well a reliable control system for biogas production.

Potential Impact:
The OPTI-VFA project has delivered to precompetitive prototype scale an affordable PFPI-ATR tool for monitoring VFAs along the biogas and VFA production processes as well as a control solution for improving biogas production. A major feature of the system is that no sample pretreatment e.g. filtration is required. Further development and industrialization work is required in order to arrive at a fully commercial system, with a particular recommendation being the minimizing the effect of the optical fibres as well as the effects of ambient humidity and temperature to instrumentation in an anaerobic digestion process.
Moreover the potential for system to be used in the monitoring of fermentable sugar production e.g. in lignocellulosic biorefineries, which are being commercialized globally and the fermenting of wine, beer, distilled beverages, brandies, sweet liquors, and juices is high, enhances the exploitation possibilities of the OPTI-VFA project results.
There are numerous socio-economic impacts that will be derived from the results of this OPTI-VFA research project. Central to the expected socio-economic impact, is the boosting of the competitiveness of companies operating along the AD chain. The number of AD plants in Europe has been estimated to be approx. 40 000 in 2020. The major impact of the developed OPTI-VFA comes to the end-user AD operators by increased profitability. The modest estimation is that throughput of waste in the digesters could be increased by 10% that in turn would increase the production of biogas approximately with the same factor. Another possibility is to switch from biogas production to VFA recovery in agroindustrial anaerobic digesters by means of OPTI-VFA on-line monitoring. The OPTI-VFA project will be helpful in achieving a more sustainable society, that is: efficient use of all organic residues, such as recuperation of VFAs from organic residue, and simultaneous reduction of organic waste emissions. After digestion, waste has considerably less odour problems, reduced acidity as well as reduced pathogen and pesticides content. Fossil fuels can be compensated by biogas and thus the amount of emissions can be decreased. Also the methane emissions will be decreased, when the methane produced as a disintegration product during AD process will be utilized as energy in a closed process.
A key importance was given to the management of the intellectual properties and in agreement of the dissemination of non-confidential information throughout the project. The project developed significant know-how that will be exploitable by the SMEs. A preliminary business plan, as well as a post project development work, has been laid out. The synergistic role of the partners covering the whole supply and value chain has been discussed. E.g. the simulation methodology together with the control solution will allow the participating SME to offer this result in a great diversity of AD plants (not only in farm-scale AD plants but also in sludge treatment anaerobic digesters, AD plants treating industrial wastewaters, etc.).
The OPTI-VFA project has been actively disseminated by all partners throughout the project, through a variety of channels e.g. the project website, press releases, leaflets, and a number of attendance to conferences and meetings and to the defined target audiences. Post-project, OPTI-VFA will continue to be disseminated, especially as a means for facilitating project-project exploitation of the results.

List of Websites:
www.opti-vfa.eu
For further information please contact:
D.Tech. Katariina Rahkamaa-Tolonen
VTT Technical Research Centre of Finland Ltd
Kaitoväylä 1
90571 Oulu
Finland