In this paper, the mixed integer linear programming (MILP) for solving unit commitment (UC) problems in a hybrid power system containing thermal, hydro, and wind power have been studied. To promote its efficiency, an improved MILP approach has been proposed, while the symmetric problem in MILP formulas has been solved by reforming hierarchical constraints. Experiments on different scales have been conducted to demonstrate the effectiveness of the proposed approach. The results indicate a dramatic efficiency promotion compared to other popular MILP approaches in large scale power systems. Additionally, the proposed approach has been applied in UC problems of the hybrid power system. Two indexes, fluctuation degree and output degree, have been proposed to investigate the performance of renewable energy sources (RES). Several experiments are also implemented and the results show that the integration of pumped hydroelectric energy storage (PHES) can decrease the output of thermal units, as well as balance wind power fluctuation according to the load demand.

This study presents an investigation on the effect of heavy metals on the production of biogas during the process of anaerobic digestion (AD) of olive mill waste (OMW). The poisonous effect and the inhibitory influence of Fe, Ni, Pb, Zn, Cu, and Cr on the digestion process are investigated and determined. Biomethanation potential tests are performed for this sake. Adding some of the heavy metals to the AD decreases the efficiency of biogas production and methane concentration and decreases the reduction in the VS, the TCOD, the SCOD, and the organic acid load. A critical increase in the total organic acid and inhibition of methanogenic bacteria was observed due to its toxicity. The toxicity of the heavy metals can be arranged according to increasing order: Cu > Ni > Pb > Cr > Zn > Fe, which leads to rapid poisoning of the active microorganisms. Iron may also exhibit stimulatory effects, but with a low rate and at a certain level. The conclusions of this work are important for the industry and help to understand how to carefully manage the presence of heavy metals in the digestate.

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