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Agricultural crops and forest residues are of valuable resources to produce biofuel due to anaerobic digestion. But, the recalcitrance nature of these lignocellulose residues limits its enzymatic degradation. Therefore, efficient pretreatments prior to anaerobic digestion are essential. Hydrothermal-chemical pretreatments using Phenol (Ph), Sodium Hydroxide (SH), and Phosphoric Acid (PA), and combined pretreatments included Ph+SH and Ph+PA as chemical pretreatments were used for spruce wood. The samples were put into the autoclave at 134ºC for 20 min. Acid hydrolysis, FTIR and SEM analyses were carried out. The results indicated that all pretreatments were effective lignin removal having the highest value for Ph (42.362%). Adding Ph to PA increased lignin removal from 1.580% to 6.112%. Mixing Ph to SH represented the same trend in changing structure of spruce wood as compared to individually SH. All results proposed that when Ph contributed in binary pretreatment with SH and PA, it could be more effective on the morphological changes of spruce wood. In general, Ph was more effective on changing the crystalline structure of spruce wood than the others. After that, Ph+SH was more effective compared to Ph+PA on structural changes. In comparison between alkali and acidic pretreatments, SH represented more structural change in spruce wood than PA one. To decreased toxicity of Ph, it is recommended to use the combination of Ph with SH as infectious pretreatment instead of individually Ph. Because, this increases the biodegradation power of SH while the toxicity of Ph decreases. The results are very important in biogas production systems. [ABSTRACT FROM AUTHOR]