Real-Time Assessment of Compost Maturity Using a Low-Cost CO₂ Sensor: A Comparative Evaluation of Microbial Starters

The composting process involves biochemical degradation in complex aerobic conditions, where carbon components are transformed into carbon dioxide (CO2). Fluctuations in CO2 emissions during composting serve as important indicators for determining the level of maturity and effectiveness of compost. This study employed a using a Randomized Complete Block Design (RCBD) consisting of a 4x7 factorial design. The first factor represented the variation in starter types, while the second factor corresponded to the differences in fermentation duration during composting. Four microbial starters were evaluated: EM4, eco-enzyme, Stardec, and Trichoderma. The fermentation time used for composting ranged from 1-7 days. This study observed the quality of compost element contents, including C-organic, N-total, P2O5, and K2O, along with the level of water content, pH, temperature, and CO2 emissions. The results showed that variation in starter types produced a significant effect (P<0.05) on C-organic (18.32–24.39%), P₂O₅ (1.91–5.05%), moisture content (23.55–56.84%), pH (6.10–7.00), and CO₂ emissions (5,083.30–17,733.80 ppm). In contrast, the fermentation period showed no significant effect (P>0.05) on all parameters, such as C-organic, N-total, P₂O₅, K₂O, moisture content, pH, and temperature, except CO2 emissions, which exhibited a significant difference (P<0.05). Nevertheless, there was a significant effect of the interaction between the starter type and fermentation time on CO₂ levels (P<0.05), indicating that the combination of the two factors influences the intensity of microbial activity during decomposition. Based on these results, it can be concluded that treatment with S3 starter and a fermentation time of 7 days produced the best results, characterized by the highest levels of CO₂ (13,553.44 ± 3,114.38 ppm), reflecting the optimal activity of the starter in decomposing organic matter. Significant correlations were observed among compost quality parameters, including a negative correlation between C-organic and both P₂O₅ (r = –0.345, P = 0.001) and CO2 emissions (r = –0.237, P = 0.030) and a positive relationship between N-total and K₂O (r = 0.386, P < 0.001). Moisture content showed a weak negative correlation with pH (r = –0.243, P = 0.026) and a weak positive correlation with CO₂ emissions (r = 0.227, P = 0.037). Building on recent advancements in sensor-based monitoring, CO2 sensors can provide real-time information on the level of activity of microorganisms in compost, while indicating the maturity stage of compost more accurately and efficiently than traditional methods.