Correlation analysis and predicting modeling of pyrolysis gas based on landfill excavated waste pyrolysis characteristics.

The contribution of excavated waste to waste management is multifaceted, including minimization, non-hazardous disposal, access to useable land resources, improved waste management techniques and public environmental awareness, consistent with recent circular economy initiatives. Pyrolysis can be converted into tar, pyrolysis gas and char with recyclable utilization, enriching the application of pyrolysis technology in the field of excavation waste. In this study, the pyrolysis system includes horizontal tube furnace, gas collection device and Micro GC. The excavated waste was pyrolyzed at a temperature of 500∼900 °C with a heating rate of 10 °C/min. Pyrolysis gases include H2, CO, CO2, CH4, C2H4, C2H6 and C3H8. Pyrolysis was divided into four stages, the main decomposition range is 230∼500 °C, with a weight loss rate of 68.49% and a co-pyrolysis behavior. As the temperature increases, the tar and char decreased and the gas production increased significantly, and the pyrolysis gas reached 47.02% at 900 °C. According to Pearson correlation coefficient analysis, the generation of H2 and CO is positively correlated with temperature. Therefore, the target products can be influenced by changing the parameters, when considering the practical utilization of the excavated waste pyrolysis products. On this basis, the prediction models were built by polynomial fitting method. This model can reduce the experimental exploration cycle, reduce the cost, and accurately predict the pyrolysis gas, which has practical guidance for the application of pyrolysis industry, and provides a theoretical basis for the resource recycling and energy recovery of landfill.

Effective Se reduction by lactate-stimulated indigenous microbial communities in excavated waste rocks.

Waste rocks generated from tunnel excavation contain the metalloid selenium (Se) and its concentration sometimes exceeds the environmental standards. The possibility and effectiveness of dissolved Se removal by the indigenous microorganisms are unknown. Chemical analyses and high-throughput 16S rRNA gene sequencing were implemented to investigate the functional and structural responses of the rock microbial communities to the Se and lactate amendment. During anaerobic incubation of the amended rock slurries from two distinct sites, dissolved Se concentrations decreased significantly, which coincided with lactate degradation to acetate and/or propionate. Sequencing indicated that relative abundances of Desulfosporosinus burensis increased drastically from 0.025 % and 0.022% to 67.584% and 63.716 %, respectively, in the sites. In addition, various Desulfosporosinus spp., Symbiobacterium-related species and Brevibacillus ginsengisoli, as well as the Se(VI)-reducing Desulfitobacterium hafniense, proliferated remarkably. They are capable of incomplete lactate oxidation to acetate as only organic metabolite, strongly suggesting their involvement in dissimilatory Se reduction. Furthermore, predominance of Pelosinus fermentans that ferments lactate to propionate and acetate implied that Se served as the electron sink for its fermentative lactate degradation. These results demonstrated that the indigenous microorganisms played vital roles in the lactate-stimulated Se reduction, leading to the biological Se immobilization treatment of waste rocks.

Stabilization of heavy metals during co-pyrolysis of sewage sludge and excavated waste.

In this paper, excavated waste was added to sewage sludge for co-pyrolysis, aiming to stablize the heavy metals in sewage sludge. The effect of co-pyrolysis with various pretreatment (e.g. cooling, drying and hydrothermal pretreatment) on heavy metals stabilization was studied using orthogonal test. The results showed that the optimal conditions are 600 °C, nitrogen flow rate of 200 mL/min, mixing excavated waste with sewage sludge (25:75, wt%) and hydrothermal pretreatment. 90% of the heavy metals in the sewage sludge and excavated waste mixtures were transformed to biochars after co-pyrolysis. Moreover, the state of heavy metals changed from bio-available fractions to stable state, thereby reducing the potential ecological risk index (RI) from 116.8 to below 50, which represented a reduction in contamination levels and ecological risks from considerate to low. Finally, the study found that the synergy between hydrothermal and pyrolysis made full use of the moisture in sewage sludge and was more conducive to the solidification of heavy metals. This paper provides a good option to dispose multiple wastes and reduce their environmental risks.