Impact of temperature on the performance of compost-based landfill biocovers

Integrating bioprocess and metagenomics studies to enhance humic acid production from rice straw

Rice straw burning annually (millions of tons) leads to greenhouse gas emissions, and an alternative solution is producing humic acid with high added-value. This study aimed to examine the influence of a microbial consortium and other additives (chicken manure, urea, olive mill waste, zeolite, and biochar) on the composting process of rice straw and the subsequent production of humic acid. Results showed that among the fungal species, Thermoascus aurantiacus exhibited the most prominent impact in expediting maturation and improving compost quality, and Bacillus subtilis was the most abundant bacterial species based on metagenomics analysis. The highest temperature, C/N ratio reduction, and amount of humic acid production (Respectively in lab 61 °C, 54.67%, 298 g kg-1 and in pilot level 65 °C, 72.11%, 310 g kg-1) were related to treatments containing these microorganisms and other additives except urea. Consequently, T. aurantiacus and B. subtilis can be employed on an industrial scale as compost additives to further elevate quality. Functional analysis showed that the bacterial enzymes in the treatments had the highest metabolic activities, including carbohydrate and amino acid metabolism compared to the control. The maximum enzymatic activities were in the thermophilic phase in treatments which were significantly higher than that in the control. The research emphasizes the importance of identifying and incorporating enzymatically active strains that are suitable for temperature conditions, alongside the native strains in decomposing materials. This strategy significantly improves the composting process and yields high-quality humic acid during the thermophilic phase.

Manipulating soil microbial community assembly by the cooperation of exogenous bacteria and biochar for establishing an efficient and healthy CH4 biofiltration system

Manipulating the methanotroph (MOB) composition and microbial diversity is a promising strategy to optimize the methane (CH4) biofiltration efficiency of an engineered landfill cover soil (LCS) system. Inoculating soil with exogenous MOB-rich bacteria and amending soil with biochar show strong manipulating potential, but how the two stimuli interactively shape the microbial community structure and diversity has not been clarified. Therefore, three types of soils with active CH4 activities, including paddy soil, river wetland soil, and LCS were selected for enriching MOB-dominated communities (abbreviated as B_PS, B_RWS, and B_LCS, respectively). They were then inoculated to LCS which was amended with two distinct biochar. Besides the aerobic CH4 oxidation efficiencies, the evolution of the three microbial communities during the MOB enrichment processes and their colonization in two-biochar amended LCS were obtained. During the MOB enriching, a lag phase in CH4 consumption was observed merely for B_LCS. Type II MOB Methylocystis was the primary MOB for both B_PS and B_LCS; while type I MOB dominated for B_RWS and the major species were altered by gas concentrations. Compared to biochar, a more critical role was demonstrated for the bacteria inoculation in determining the community diversity and function of LCS. Instead, biochar modified the community structures by mainly stimulating the dominant MOB but could induce stochastic processes in community assembly, possibly related to its inorganic nutrients. Particularly, combined with biochar advantages, the paddy soil-derived bacteria consortiums with diverse MOB species demonstrated the potent adaption to LCS niches, not only retaining the high CH4-oxidizing capacities but also shaping a community structure with more diverse soil function. The results provided new insights into the optimization of an engineered CH4-mitigation soil system by manipulating the soil microbiomes with the cooperation of exogenous bacteria and biochar.