India faces a significant challenge in managing its municipal solid waste, including a substantial amount of vegetable market waste (VMCW). A large portion of this waste ends up in landfills, contributing to increased landfill loading and greenhouse gas emissions. Composting offers an effective alternative for managing this organic waste, converting it into a valuable soil amendment. Traditional composting methods, however, are time-consuming. This research aimed to accelerate the composting process of VMCW using enzyme-mediated aerobic composting. The study's significance lies in exploring a faster and more efficient composting technique to mitigate environmental problems associated with VMCW disposal and to produce a nutrient-rich compost. The hypothesis was that the use of a pre-cultured seed inoculum would significantly reduce the composting time while maintaining or improving the quality of the resulting compost. The large volume of VMCW generated daily in India necessitates efficient and rapid composting methods. This study intends to provide a solution by shortening the composting time and improving the quality of the end product.

Existing literature extensively documents the benefits of aerobic composting in managing organic waste. Studies have shown that composting reduces greenhouse gas emissions, enhances soil fertility, and improves soil productivity (Finstein et al., 1983; Kayhanian et al., 1992; Elving et al., 2010). Researchers have investigated various approaches to optimize the composting process, including the use of designed reactors and the addition of microorganisms to accelerate decomposition (Finstein et al., 1983; Kayhanian et al., 1992; Elving et al., 2010). The addition of seed inoculums to enhance microbial populations and enzyme activity has also been explored, resulting in shorter composting times and reduced odor emissions (He et al., 2013; Ohtaki et al., 1998). However, research on enzyme activation and biokinetic modeling in aerobic composting is relatively limited. This study builds upon existing research by developing and utilizing a novel pre-cultured seed inoculum designed to specifically degrade VMCW, aiming for a significant reduction in composting time.

The study employed a multi-stage process, beginning with the collection of VMCW from Tambaram Municipality, Chennai, India. Stratified random sampling ensured sample representativeness. The collected VMCW was subjected to a two-stage shredding process, reducing its size to approximately 0.5–0.6 cc. A specially designed and fabricated aerobic composting reactor made of SS316 (45 × 30 × 60 cm L × B × H) was used. The reactor incorporated a manual stirring lever and a continuous aeration system to maintain uniform mixing. A pre-cultured seed inoculum, prepared using jaggery and curd, was added to the reactor along with a bulking agent (rice husk) to enhance microbial activity. A 12 kg sample of shredded VMCW was mixed with the inoculum in a 16:1 ratio and placed in the reactor. Composting parameters such as pH, total solids (TS), volatile solids (VS), volume reduction, and temperature were monitored daily at various depths. Various analytical methods were used to characterize the VMCW and compost, including the determination of total solids, volatile solids, fixed solids, moisture content, organic matter, pH, and elemental composition (C, H, N, S) using a CHNS analyzer. The calorific energy value (CEV) was estimated using a formula proposed by Channiwala et al. (2002). X-ray diffraction (XRD) analysis was used to assess the structural changes during composting. Microbial growth was monitored using nutrient agar plates. Finally, biokinetic modeling was performed to analyze the efficiency of the inoculation process.

The study successfully reduced the aerobic composting time to 9 days from the traditional 45 days using the pre-cultured seed inoculum. A significant 42% reduction in organic matter (from 82 ± 2.83% to 40.82 ± 0.61%) and a substantial volume reduction from 0.012 m³ to 0.003 m³ were observed within 9 days. The resulting compost exhibited enhanced nutrient levels: 0.91% w/w nitrogen, 0.5% w/w phosphorus, and 1.029% w/w potassium. XRD analysis confirmed the transformation of the compost particle's crystal structure to an amorphous form and the mineralization of organic matter. Initial decomposition was carried out by mesophilic microorganisms, followed by a thermophilic stage reaching 54 ± 9.27 °C on the third day. The moisture content decreased significantly (64%) on the 3rd day due to high temperatures and microbial activity. The initial pH of 6.8 decreased to 6.23 on the second day due to rapid hydrolysis and increased hydrogen ion concentration, and gradually increased to 7.8 by the end. The C/N ratio decreased from 13.84 to 2.35, indicating compost maturity. A high correlation was observed between volatile solids and volume reduction (R² = 0.862) and between volatile solids and CEV (R² = 0.913). Microbial growth rate peaked on the 4th day (3.47 × 10⁶ CFU/g), aligning with high VS reduction, volume reduction, and optimal temperature, pH, and C/N ratio. Biokinetic modeling yielded Michaelis-Menten constant (Km) of 81.06 and limiting velocity reaction rate constant (Kcat) of 0.15.

The findings demonstrate the effectiveness of the pre-cultured seed inoculum in accelerating the VMCW composting process. The significant reduction in composting time, combined with improved nutrient levels in the resulting compost, offers a practical and environmentally sound solution for managing VMCW. The enhanced microbial activity, facilitated by the inoculum, led to faster degradation of organic matter and efficient nutrient mineralization. The high correlation between volatile solids, volume reduction, and CEV further supports the effectiveness of the approach. The study's success in producing mature compost with enriched NPK levels within 9 days offers a significant improvement over traditional methods, making it a viable and economically attractive alternative for VMCW management. This approach contributes to reducing landfill burden, mitigating greenhouse gas emissions, and producing a valuable fertilizer.

This study successfully demonstrated a novel approach for accelerating the aerobic composting of VMCW using a pre-cultured seed inoculum derived from jaggery and curd. The significantly reduced composting time, increased nutrient content, and efficient organic matter degradation highlight the potential of this method for sustainable waste management. Future research could explore scaling up this method for large-scale applications and further optimizing the inoculum formulation for improved performance and wider applicability.

The study was conducted on a laboratory-scale composting reactor. The results may not directly translate to large-scale composting operations. The specific composition of the VMCW might influence the composting process, necessitating further investigation with variations in waste composition. The study focused on VMCW; further research is required to determine the applicability of the developed technique to other types of organic waste.