Microbial and enzymatic dynamics during kitchen waste vermicomposting with contrasting carbon-rich substrates: Implications for biodegradation and quality

Abstract In sub-Saharan African cities, managing the growing volume of kitchen waste remains a critical challenge. This study evaluated the microbial and enzymatic profile during vermicomposting of organic kitchen waste (OKW) using the African earthworm Eudrilus eugeniae , specifically testing the impact of three carbon-rich amendments: grass clippings, sawdust, and cardboard waste. Conducted at the University of Yaounde I (Cameroon), the 60-day experiment compared five treatments (T0-, T0+, T1, T2, T3) to track microbial dynamics and the activity of five key enzymes (amylase, cellulase, protease, urease, and alkaline phosphatase) across three phases (Day 0, Day 30, and Day 60.). Morphological and biochemical identification revealed three species of bacteria, Azotobacter sp., Bacillus sp., and Actinomyces sp.; three species of fungi ( Fusarium sp., Penicillium sp. and Aspergillus sp.) and three faecal coliform strains ( Klebsiella sp., Escherichia coli . and Enterobacter sp.). The total coliform counts fell below WHO safety thresholds (< 1,000 CFU g⁻¹) in all treatments by day 60, validating the proces’s sanitation efficiency. Enzymatic kinetics varied significantly by phase: urease peaked during pre-composting, protease at day 30, while amylase, cellulase, and phosphatase reached maximum activity at maturity (day 60). Cardboard (T3) and sawdust (T2) amendments produced the most distinct enzymatic signatures, with T3 showing the highest cellulase activity (7208.65 ± 57.53 µg/g dry weight glucose). These findings indicate that the choice of carbon amendments significantly modulates microbial structure and enzymatic speed, directly influencing the biodegradation rate and the final quality of the vermicompost.