Trace elements are important components to increase biomethane production performance. Their reactor-specific required concentrations should be determined for each application. In this study, the effects of trace element addition on biogas and biomethane production in an anaerobic reactor treating paper industry wastewater were investigated. The study was conducted by operating multiple batch reactors and using the Box-Behnken experiment design method. The biogas and biomethane responses (R-2 values) were 0.9506 and 0.9374, respectively, indicating that the Box-Behnken model was significant. While influent COD and VSS were 2594 +/- 180.8 and 2885 +/- 16.45 mg/L, optimum Fe, Cu, Ni, Co, and Mg concentrations were 196.8, 0.01, 1.30, 1.31, and 50.63 mg/L, respectively. For biogas and biomethane production, 11 +/- 0.27% and 18 +/- 0.45% increases were observed in reactors with trace elements added, compared to the control, respectively. Biogas and biomethane production rates were also monitored with 15-day kinetic studies. From day 9 to 15, the reactor with trace elements added became superior to the control group by means of daily biogas and biomethane production. The microbial community of the reactor biomass was investigated with 16S V3-V4 rRNA targeted metagenomic analysis and the dominant species was Methanosaeta thermophila (an acetate utilizing bacteria) with a rate of 38.05%.