Relating bacterial dynamics and functions to gaseous emissions during composting of kitchen and garden wastes

Highlights: • Garden waste addition at 15% (wet weight) notably improved kitchen waste composting. • NH₄⁺, temperature, oxygen content and EC significantly impact gaseous emissions. • Anaerobes in raw kitchen waste contributed significantly to CH₄ and N₂O emissions. • Co-composting garden and kitchen wastes reduced bacteria with gaseous emissions. • FAPROTAX analysed microbial functions to decipher the reduced gaseous emissions. This study aims to relate bacterial dynamics to gaseous emissions during the composting of kitchen and garden wastes. High-throughput sequencing and Functional Annotation of Prokaryotic Taxa (FAPROTAX) were used to analyse the bacterial community and potential functions during composting, respectively. Results show that the addition of garden waste up to 15% of the total wet weight of composting materials notably mitigated gaseous emissions and improved maturity during kitchen waste composting. Ammonium nitrogen, temperature, oxygen content, and electrical conductivity were identified as critical factors to impact gaseous emissions. The bacterial community analysis indicated that the proliferation of anaerobes during the storage of kitchen waste induced the dramatic emission of methane (CH₄) and nitrous oxide (N₂O) at the beginning of composting. Adding garden waste could effectively amend the physiochemical properties of composting materials to reduce the relative abundance of microbes (e.g. Desulfotomaculum and Caldicoprobacter) that contributed to gaseous emissions, but enrich those (e.g. Bacillus and Pseudoxanthomonas) for organic biodegradation. Further analysis by FAPROTAX corroborated that adding garden waste could effectively inhibit relevant microbial metabolisms (e.g. fermentation, nitrite/nitrate respiration and sulphate respiration) and thus alleviate the emission of greenhouse gases and odours during kitchen waste composting.