Application of Methane Fermentation Technology in Pulp and Paper Iindustry: Treatment of a Mixture of Hardwood and Softwood Kraft Pulp Mill Evaporate Condensate

摘要

Recent development of methane fermentation technology has made wastewater treatment highly effective; therefore, this technology is applied widely in many industries. The advantages are recovering energy as biogas from organic compounds of wastewater and keeping residual sludge at a lower amount than an aerobic treatment system. It was decided to introduce methane fermentation technology to treat Kraft Pulp (KP) mill evaporate condensate because of its recent improvements. First, it was introduced in the Yufutsu mill, which produces only hardwood KP. This was the second case that methane fermentation was applied in a KP mill in the world. Next, the process was introduced in the Iwakuni mill, which produces hardwood and softwood KP. In this study, each mill's evaporate condensate was analyzed. It was found that the evaporate condensates from the hardwood and softwood KP mill contained more resin acids, diterpene and sesquiterpene than that from the hardwood KP mill. Because these substances might deteriorate methane fermentation, the optimum conditions to treat the hardwood and softwood KP mill's evaporate condensate were first investigated in a pilot plant. The evaporate condensate was able to be treated continuously and COD was removed stably, even at a high loading rate. Based on these results, we started using the process at the operation plant at the Iwakuni mill, which has been running successfully.