# Application of Near-Infrared Spectroscopy for Monitoring and/or Control of Composting Processes
## 5 Use of NIR Spectroscopy to Monitor and/or Control the Composing Process
Window composing (manual composting technology, Figure 3) was performed using 4 m high and 8 m diameter piles composed of 68% olive pomace, 24% goat manure, 6% olive tree pruning, and 2% chicken excrement mixed with sawdust for a one year. The results indicated that the FT-NIR and FT-MIR combination of data is especially dependent on molecular modifications occurring both during and following the composting procedure, and PCA analysis of the merged spectra indicated that the changes below 175 \({}^{\circ}\)C are mostly caused by water loss, whereas heating above 225 \({}^{\circ}\)C causes a drop in the aliphatic groups. Both examples confirm that the NIRS operational technique is relatively easy and nondestructive, and the measurement takes just a few minutes and can be used for the continuous monitoring of the composting process, as presented for the chicken manure samples in Figure 5 [71]. Another example of the efficient usage of handheld near-spectroscopy for the monitoring of industrial composting processes was presented by [PERSON] et al. [74]. The authors stated the potential of the used handheld NIR in the accurate detection of the contents of (i) moisture, (ii) total nitrogen, (iii) total carbon, and (iv) organic matter as well the ratio of C/N and changes in electrical conductivity during the composting process. Their results showed that NIR spectroscopy described the moisture content with the highest accuracy, followed by total nitrogen and organic matter. The possibility of the rapid measurement of moisture content during the composting process is considered very important, taking into account that the composting process efficiency depends on moisture control. Developments in the NIR instrumentation production led to the production of high performance portable NIR spectrometers [75]. The use of portable devices for in-field measurements opens up new opportunities by allowing the direct measurement of critical parameters. These devices offer various benefits, including lower costs, enhanced safety for the environment and workers, and improved  
Figure 5: NIR spectra of chicken manure samples during composting presented by [PERSON] et al. [71]. Different line colors present different days of composting. technique accuracy by conserving the sample and eliminating its travel. Similarly, [PERSON] et al. [75] investigated the ability of a field-portable NIR spectrophotometer to identify the nutrient content of unprocessed, stored (not turned), and composted cattle feedlot manure. NIRS was discovered to be helpful in two distinct manners. SIMCA (Figure 4), utilizing spectral data alone, revealed that stockpiling the manure did not considerably alter it, whereas compost was considerably distinct from the raw or stored manure. Second, usable calibrations for total carbon (C), organic carbon, total nitrogen (N), the carbon/nitrogen ratio (C/N), sulphur (S), potassium (K), and pH were created by merging spectral and compositional data depicting raw, stored, and composted cattle manure for both years. These calibrations can be used to forecast these constituents in fresh samples in real time. The data available in the literature also show that NIR spectroscopy can be used for the estimation of available nitrogen in poultry manure compost [76]. Second derivative spectra and multiple regression analysis were applied to establish highly precise calibration models for total nitrogen and uric acid nitrogen in compost. According to [PERSON] et al. [77], under the same measurement settings, the performance of the laboratory and portable NIR devices is equivalent. Nonetheless, depending on the measurement settings and sample characteristics, NIR spectrometers in the field may confront additional issues inherent in situ measurements, which may bring undesirable fluctuations into the spectra that have to be removed by applying some of the spectra preprocessing methods. [PERSON] et al.