The interaction between temperature and citric acid treatment in the anaerobic fermentation of Chinese cabbage waste

Temperature is a crucial environmental factor for recycling Chinese cabbage waste. Herein, we evaluated the impacts of temperatures (15, 25 and 35 °C) on the effects of citric acid treatment (1.11% dry matter) on the anaerobic fermentation of Chinese cabbage waste. The results indicated that citric acid treatment improved the acetic acid concentration, reduced the ammonia nitrogen levels, upregulated lipid metabolism, and increased the Lactobacillus and Pediococcus abundances but reduced the Weissella, Naumovozyma, Monascus and Alternaria abundances during the anaerobic period. After aerobic exposure, citric acid treatment during the anaerobic period at 15 and 35 °C improved aerobic stability, reduced organic acid degradation, inhibited ammonia nitrogen formation, upregulated replication and repair pathways, enhanced the competition among fungi, and increased the Acetobacter, Naumovozyma and Kazachstania abundances but reduced the Bacillus, Pseudomonas and Trichosporon abundances; citric acid treatment during the anaerobic period at 25 °C enhanced aerobic deterioration, resulted in a 77.12% (p < 0.05) increase in the pH value and a 167.71% (p < 0.05) increase in the ammonia nitrogen content, upregulated amino acid metabolism, enhanced commensalism or mutualism between bacteria and fungi, and enriched Zygosaccharomyces and Bacillus. Collectively, citric acid treatment at 15 and 35 °C improved short-chain fatty acid production, improved aerobic stability and reduced alkaline pollutant generation during Chinese cabbage waste fermentation, whereas at 25 °C, it exacerbated aerobic deterioration, which was associated with variations in dominant microbes, microbiome topologies and functional pathways.