Bacterial Community Structure and Predicted Metabolic Function of Landfilled Municipal Solid Waste in China

Breakthrough times for barrier systems at typical municipal solid waste landfills in China

Landfill is the most common disposal method for municipal solid waste (MSW). Composite liners are widely used as bottom barriers in MSW landfills in China to minimize groundwater contamination with landfill leachate. However, little information is available on breakthrough times for bottom barrier systems used in landfills. In this study, breakthrough times for bottom barrier systems used in typical active MSW landfills in four Chinese cities (Hangzhou, Shanghai, Shenzhen, and Suzhou) were evaluated by numerically modelling chemical oxygen demand (COD) transport. The performances of the landfill bottom barrier systems were determined from the COD concentration of the leachate, the landfill operating period, and the leachate head. A leachate head of 0.3 m is specified in the relevant regulations. Using a leachate head of 0.3 m, the breakthrough times for the barrier systems in all of the four landfills were > 50 years. However, using the actual leachate heads, the breakthrough time for the barrier system in the Hangzhou landfill was only 27 years even though the barrier system was a compacted clay liner/geomembrane/geosynthetic clay composite liner. The results of this study provide reference data for designing and managing landfill barrier systems.

Coupled effect of microbiologically induced calcium carbonate and biofilms in leachate

Fouling and clogging are persistent challenges to the collection and treatment of leachate. The main components of fouling and clogging are calcium carbonate (CaCO₃) and biofilms. However, the relationships between CaCO₃ and biofilms remain to be clarified. In this study, the interaction between microbially induced CaCO₃ precipitation (MICP) and biofilms was investigated using Luria-Bertani (LB) or urea media. Results showed that the bacteria promoted the precipitation of CaCO₃ and the formation of a complex mixture of biofilms. The amount of formed CaCO₃ in the urea medium was 12.9 times of that in the LB medium. The high MICP potential in the urea medium was associated with increased pH and alkalinity. In addition, the clogging materials exhibited a layered structure and uneven distribution over the clogging width and depth profile. These results indicated the presence of nucleation sites of CaCO₃ on the surface of and inside the bacteria. This research provides insights into the regulation of MICP and biofilms through dynamic control of clogging and fouling.

Spatial Variation of Microbial Community Structure and Its Driving Environmental Factors in Two Forest Types in Permafrost Region of Greater Xing′an Mountains

Climate warming is accelerating permafrost degradation. Soil microorganisms play key roles in the maintenance of high-latitude permafrost regions and forest ecosystems’ functioning and regulation of biogeochemical cycles. In this study, we used Illumina MiSeq high-throughput sequencing to investigate soil bacterial community composition at a primeval Larix gmelinii forest and a secondary Betula platyphylla forest in a permafrost region of the Greater Xing’an Mountains. The Shannon diversity index tended to decrease and then increase with increasing soil depth, which was significantly higher in the L. gmelinii forest than in the B. platyphylla forest at 40–60 cm. Proteobacteria (19.86–29.68%), Acidobacteria (13.59–31.44%), Chloroflexi (11.04–27.19%), Actinobacteria (7.05–25.57%), Gemmatimonadetes (1.76–9.18%), and Verrucomicrobia (2.03–7.00%) were the predominant phyla of the bacterial community in two forest types. The relative abundance of Proteobacteria showed a decreasing trend in the B. platyphylla forest and an increasing trend in the L. gmelinii forest, whereas that of Chloroflexi increased and then decreased in the B. platyphylla forest and decreased in the L. gmelinii forest with increasing soil depth. The relative abundance of Acidobacteria was significantly higher in the B. platyphylla forest than in the L. gmelinii forest at 0–20 cm depth, whereas that of Actinobacteria was significantly higher in the L. gmelinii forest than in the B. platyphylla forest at 0–20 cm and 40–60 cm depth. Principal coordinate analysis (PCoA) and two-way analysis of variance (ANOVA) indicated that microbial community composition was more significantly influenced by forest type than soil depth. Redundancy analysis (RDA) showed that microbial community structure was strongly affected by soil physicochemical properties such as nitrate nitrogen (NO3−-N), pH, and total organic carbon (TOC). These results offer insights into the potential relationship between soil microbial community and forest conversion in high latitude permafrost ecosystems.