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A novel anaerobic DIGESTer solution in AIR transport for on-board safe and efficient waste management

Periodic Reporting for period 2 - DIGESTAIR (A novel anaerobic DIGESTer solution in AIR transport for on-board safe and efficient waste management)

Reporting period: 2020-04-01 to 2021-09-30

Digestair aims to implement an Anaerobic Digestion prototype ready for aircraft testing that will allow the sewage and waste valorization that are generated in commercial flights.
The main general conclusions of the project are as follows: it is possible to design a waste treatment system on board an aircraft for biomethane production, but further studies are needed to determine the technical and economic feasibility of the solution. The major challenge is to couple the times required for the treatment of the aircraft waste with the flight periods and the management of the biomethane generated. Computer simulation tools make it possible to study the process for different system operation scenarios: short flights, long flights, with different occupancy levels, etc. Finally, the solution would be easier to implement on ships, due to their size and longer operating times.
The main achievement during the project period has been the construction completion of the DIGESTAIR prototype and its commissioning with real waste, as planned in the DOA. The steps required to achieve this goal are summarized below:
(i) Completion of the assembly of all the components.
(ii) Completion of the installation of the electrical panel and the wiring and automation of all the components of the prototype.
(iii) Programming of the operating automatisms in the PLC (Programmable Logic Controller) of the prototype.
(iv) First operating tests of critical units using water: vacuum transfer system, pasteurization, membrane filtration system.
(v) Inoculum collection and conditioning. Specifically, inoculum was collected from the anaerobic digestion plant for the treatment of the organic fraction of municipal solid waste in San Sebastian. The inoculum has been characterized, and it has been necessary to sieve it, filter it and make a partial dilution to remove undesired contaminants.
(vi) The individual waste streams have been adequately characterized and the BMP tests results showed a higher biogas and methane potential for food waste > bioplastic > manure, where the highest methane production was obtained at mesophilic temperature.
(vii) Collection of waste to be treated in the experimental prototype: food waste from catering, biodegradable plastics and cardboard, pig slurry as "black water", and preparation of the influent mixture according to the previous study carried out to determine the composition of waste generated on board.
(viii) Start-up of the prototype with the conditioned inoculum and the prepared waste mixture.
(ix) Experimental validation of the prototype fed with real waste, similar to that generated in aircraft.
(x) Construction of the calibration layout of the mathematical simulation model: the model that will was used to calibrate the anaerobic co-digestion was constructed by using the WEST® simulation platform under the Plant-Wide Modelling (PWM) methodology developed by Ceit.
(xi) Calibration/Validation of the model: The experimental calibration of the model has consisted in the estimation of the values of the unknown parameters of the mathematical model that make their predictions and reproduces the experimental observations as much as possible.
(xii) Construction of the global DIGESTAIR solution model: the model that have been used to reproduce the functioning of the whole system was constructed by using the WEST® simulation platform under the PWM methodology.
(xiii) Scenario analysis by simulation: Once the anaerobic digestion was calibrated, it was possible to carry out the simulation studies. This evaluation has been based on the following aspects: (1) Determination of the feasibility of proposed technologies -DIGESTAIR solution- to treat the waste generated during the flight; (2); Definition of the optimal theoretical operating conditions of the two-stage anaerobic digestion configuration and the membrane configuration; (3) Comparison of the performance of such treatments in different conditions (different types of flights); (4) Assessment of the transferability of the ADP to other applications such as cruises.
Regarding the exploitation plan, the cost-benefits analysis has been done taking into account three periods: the industrialization period, the entry into market (short & mid-term comprising product launch and references creation) and settlement and consolidation in the market (sales period). In addition, R&D efforts from this project till industrialization would be added to embrace the overall remaining envisage activities since now and finishing with DIGESTAIR maturity enough to propose industrialization. This phase is envisaged to encompass about two years. During the industrialization period, the outcomes of DIGESTAIR will be brought from a TRL6 to a TRL8. This means important expenses in engineering, and material and subcontracting. It will also last another two years.
Finally, numerous dissemination actions have been carried out during the project, including a presentation at 3 international conferences, an article in the most widely read newspaper in Spain and a radio interview.
AD technologies are a well-known for on-ground applications. The project development relied on the extended experience that is documented on the field of AD technology, which is represented by numerous full-scale or industrial applications and commercial AD plants that are currently running for: municipal solid waste treatment, municipal sewage sludge treatment, agro-food waste treatment or on-site domestic waste treatment.
The innovation of this initiative was to transfer existing technology to air transport. Due to the novelty of this concept, there were no references in the market about similar systems. The patents that the A/C manufacturers are applying for are usually optimizations of traditional collecting systems for sewage and galley waste:
The goal of the project was to develop an ADP ready for testing in an A/C environment. Taking into account the starting point, it can be considered a kick-off TRL of 3. After completion of the project, the targeted TRL 4 has been reached.
The feasibility of the idea is demonstrated at least for several scenarios by simulations. Flight duration is a key vector, driving the bio-chemical process. Medium and especially long range flights seem to be suitable for implementing AD reactors.
An anaerobic digestion process at laboratory scale and environment served to validate the mechanical system. It mounts current existing system on A/C such as vacuum suction for lavatories to manage waste.
The use of AD products (mainly methane) as alternative energy source, reducing carbon footprint, has been initially discarded. Biogas production during flights is not significant enough to propose a new engine generation just for this purpose. This line of R&D and its implications would be realistic once biogas engines implementation will be mature.
Therefore, the project focuses on the system implementation of a system for management and treatment of waste.
Example Layout WEST simulation platform
Real prototype design 3D_v2
Mathematical model_Example_acetogenesis
Example Model Calibration
Example Experimental BMP test results
Design of the unitary components of the prototype
Real prototype design 3D_v1
Schematic diagram of the prototype