Maturing and spectral characteristics of large-scale duck manure composting under different ventilation strategies

Objectives Given the inherent challenges in handling duck manure, effective ventilation measures is pivotal for the success of industrial composting process of duck manure. This pioneering investigation aims to assess the maturity and stability of compost derived from the challenging composition of duck manure and mushroom waste. The study further scrutinized the efficacy and efficiency of various ventilation strategies in promoting the decomposition and transformation of organic matter during composting.

Methods Duck manure and mushroom waste were blended in dry weight ratio of 2∶1 (C/N ratio about 21.15) for composting experiment. The composts were in trapezoidal piles in volume of 5.6 m³ per pile, and pipes were installed for ventilation. Four ventilation duration treatments were included, as 10, 20, 30, and 60 min/d (denoted as C1, C2, C3, and C4, respectively). The changes that occurred during composting were investigated through physiochemical properties, recording of UV-visible spectroscopy, X-ray diffraction (XRD), and infrared spectroscopy (IR).

Results On the 5^th and 6^th day, compost mixtures entered thermophilic phase, which lasted 17 days and reached 50℃ on 15^th. pH climbed quickly from 8.5 to 12.3 in first 5 days due to duck manure protein breakdown, then progressively declined over next 20 days, precipitating between days 28 and 38 and then gently dropping until the compost concluded. After the high-temperature phase (day 17), compost piles C1, C2, C3, and C4 lost 45.9%, 46%, 44.7%, and 43% of their starting MC. C3 and C4 exhibited much lower TC values than C1 and C2. UV absorption decreased with wavelength in all composts. Peaks in cellulose fraction X-ray diffractograms (2θ = 26.56°). These samples had more crystalline and "amorphous" cellulose, xylan, and other polysaccharides. Nitrates and carboxylic chemicals absorbed faster than aromatic or unsaturated molecules in the 200−220 nm spectral range. Double bonds C=C, C=O, and N=N caused the latter group's absorption at 250−300 nm. The absorption rate of compost is subject to variation contingent upon either initial C/N ratio or the duration of the composting process. Conversely, the absorbance at 460−480 nm indicates the humification of organic materials. Low ratios of Q2/6 or Q4/6 indicate humification process and condensation of organic matter into aromatic compounds. In IR, throughout the composting process, there is a noticeable alteration in the intensity of all bands associated with organic or inorganic functional groups. The infrared spectra exhibited a broad peak with a central wavenumber of 3400 cm⁻¹, indicating the presence of stretching vibrations associated with hydroxyl (OH) groups and water molecules. Within the spectral range of 3000 to 2800 cm⁻¹, an observable phenomenon can be observed that pertains to hydrophobic characteristics exhibited by organic compounds. The presence of bands at 2900−2850 cm⁻¹ can be attributed to the stretching vibrations of C−H aliphatic groups and aldehyde group (CHO). IR of the initial compost samples and C1, C2, C3 and C4 significantly changed during composting. There was a significant change in absorption bands due to these changes, indicating a change in structures that contribute to absorption. As a result, C3 and C4 exhibit a higher degree of stability during composting.

Conclusions Over the 65 days of composting, the compost temperature kept varying, with ventilating 60 min/d reaching the highest temperature and 60 min/d at the lowest. pH levels decreased over time due to increased ventilation, resulting in lower values for ventilating 30～60 min/d. The C/N ratio decreased gradually, indicating increased cellulose activity. XRD spectra demonstrated reduced peak intensity, reflecting cellulose decomposition. Ventilating 30～60 min/d treatment exhibited higher compost maturity, highlighting the importance of ventilation in successful composting.