One of the important factors to consider for anaerobic digestion is the lipid content of organic waste. Indeed, a large quantity of lipids makes it possible to produce more gas: this is called the methane potential, but too large a quantity can also inhibit the process. Organic waste is often very heterogeneous and of different origins (eg agriculture, food industry, canteens), which is why it must be characterized before being recycled. Currently, the lipid content of the waste is measured by the Soxhlet method, which is based on chemical extraction coupled with a separation of the various constituents of the waste in order to analyze them. However, this method is time consuming, takes several hours per sample, and requires a highly polluting petroleum-based chemical solvent.
INRAE ââresearchers are interested in the application of NMR (Nuclear Magnetic Resonance), a non-invasive and non-destructive analysis technique where the molecules of a sample, placed in a magnetic field and excited by radio frequency, emit a signal to identify them. and quantified. NMR is already widely used in the pharmaceutical and food industries, but so far it has been little used to analyze waste. The research team focused on low-field NMR, which is cheaper and uses smaller, portable equipment.
The researchers analyzed 48 samples of organic waste from different origins (eg agricultural waste, green waste, collective catering and private waste). They used NMR coupled with chemometry, a mathematical method that extracts as much information as possible from the emitted signal. These results were then compared with those obtained with the Soxhlet method. The study shows that NMR analysis coupled with chemometry is highly predictive of the lipid content of organic waste. Not only does it avoid a long pre-calibration procedure, but it is more precise and has better repeatability than the Soxhlet method. Above all, the NMR analysis is much faster (less than a minute per sample) and environmentally friendly compared to the Soxhlet method. Scientists are now looking to improve the process, in particular by eliminating the waste drying step, in order to have a transportable analysis technique that can be directly applied to anaerobic digestion sites.
Reference: Picard S, Cambert M, Roger JM, et al. Determination of the lipid content of organic waste by nuclear magnetic resonance in the time domain. Waste management. 2022; 138: 41-48. doi: 10.1016 / j.wasman.2021.11.013
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