Pilot-scale test of Passive Treatment System for AMD in Japan
Hayashi, Kentaro; Washio, Tsubasa; Kojima, Kazuhiro; Hamai, Takaya; Masaki, Yusei; Kanayama, Akihiro; Sowanaka, Masahiro; Masuda, Nobuyuki; Kobayashi, Mikio; Sakata, Takeshi
Japan Oil, Gas and Metals National Corporation, Japan
An energy and cost saving biological passive treatment system for acid mine drainage (AMD) developed by Japan Oil, Gas and Metals National Corporation (JOGMEC) is a vertical flow anaerobic process that utilizes sulfate-reducing bacteria (SRB) with rice husk as the substrate and rice bran as the organic resource of SRB. Both rice husk and rice bran are “Agricultural Waste (Agri-Waste)” in Japan. This unique passive treatment process is called “JOGMEC Process”. In addition to this process, an aerobic process of iron oxidation and removal that utilizes iron-oxidizing bacteria is applied to treat high iron content AMD. In Japan and many other countries, flat areas available for mine drainage treatment are limited due to geographic conditions. Therefore, it is necessary to introduce a compact passive treatment system with the short hydraulic retention time (HRT). Since 2016, pilot-scale tests have been carrying out at an abandoned mine site in Japan. Concentrations of dissolved metal ions in AMD of the mine are 35 - 40 mg/L iron (mainly ferrous ion), 16 - 20 mg/L zinc, and 5 - 12 mg/L copper, and the value of pH is 3.5. As the AMD contains a high concentration of iron, it is firstly removed with the aerobic process of oxidation and removal, and then the other metal ions have been removed with the anaerobic process in the subsequent stage. During the test term, the inside temperature of the anaerobic process reactor dropped to around 4°C although the atmospheric temperature dropped to around -15°C in the winter. The performance of removal of metal ions in aerobic and anaerobic process has been stably maintained even in the lowest temperature. However, zinc content in particulate compounds in the effluent gradually increased, but dissolved zinc ion concentration, which went through the membrane filter, was adequately low. These phenomena were probably caused by inadequate trapping particulate zinc sulfides in the reactor. Therefore, the reactor of anaerobic process was more expanded and thickened. In consequence, the condition of reactor was stably improved, and particulate zinc sulfides were removed more. Optimization of the bioreactor thickness and the semi-passive process to which ethanol is directly added are further studied for development of a more compact and efficient process.