Paper mills consume a lot of water, so wastewater treatment in these factories is a very important environmental issue. In order to solve these waste water, it is necessary to separate in the sedimentation tank and use a flocculant to settle the suspended solids (SS). In the process of solving, control the pH value by referring to the pH analyzer to maintain it at an appropriate level. In the past, it was necessary to clean the pH analyzer frequently because the fibers and attachments in the wastewater would adhere to the electrode.