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The study of the effect of the mechanism of urea addition to sewage sludge and sawdust-composting substrates on methane production is still limited. In the present study, the systematic investigation of the effect of urea addition (0.18, 0.9 and 1.8 kg) on methane production is discussed through the dynamics of physical properties, enzymes, and the microbial community during composting. The results showed that high urea addition (1.8 kg) suppressed methane production, with a lower rate and a shorter duration of warming in the thermophilic phase, but significantly enhanced cellulase activity, urease, and peroxidase, and promoted the degradation of organic carbon, as well as the loss of nitrogen. A high addition of urea stimulated the growth and reproduction of Sinibacillus, Pseudogracilibacillus, Sporosarcina, and Oceanobacillus. The random forest model indicated that the top six independent determinants of CH4 emissions were Methanobacterium, temperature, organic matter (OM), Methanospirillum, and NH4+-N. Furthermore, structural equation modeling displayed that NH4+-N, O2, and pH were the main physicochemical properties affecting CH4 emissions. Methanobacterium, Methanosarcina, and Methanosphaera were the main archaea, and Bacillaceae were the main bacteria affecting CH4 emissions. This study provides new insights and a theoretical basis for optimizing urea addition strategies during composting. [ABSTRACT FROM AUTHOR]

Particle deposition often takes place in a gas turbine and it varies the surface roughness which has a great impact on flow and heat transfer characteristics. The accurate prediction of particle deposition and roughness caused by deposition is very important. In this study, one algorithm is proposed to calculate the roughness height resulting from the deposited particles which is predicted by the critical viscosity deposition model. The effect of roughness is coupled into governing turbulent equations through the specific dissipation by UDF. The particle deposition law, the corresponding roughness height, and its effects are discussed. The results show that the particles deposit along the leading edge and the deposition extends to the rear part after a strip of no-deposition region on the pressure side. On the suction side, there is much less deposition. The deposition on the tip is significantly affected by the tip flow characteristics including tip separation vortex and leakage vortex. The deposition is becoming more with the diameter of particle. The roughness height corresponding to the deposition is calculated and has similar pattern with deposition. Moreover, the number of particles deposited on the rough wall is more than that in other areas with time. This leads to more and more particles accumulated in the areas over time to form the roughness surface which then enhances the heat transfer. In return, the temperature influences the deposition and the roughness, all of which are undesirable in a turbine. [ABSTRACT FROM AUTHOR]