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Hayashi, K., T. Washio, K. Kojima, Y. Masaki, A. Kanayama, T. Hamai, M. Kobayashi, et al.
Proceedings of the International Mine Water Association (IMWA) Conference, 15-19 July, Perm, Russia, 2019

A passive treatment system was developed to remove metal ions contained in acid mine drainage (AMD) as sulfides by using sulfate-reducing bacteria (SRB). A 300-day field test conducted on anaerobic reactors filled with rice bran and rice husk successfully remediated AMD with hydraulic retention time (HRT) of 50 hours. A pilot-scale demonstration began in November 2016 at an abandoned mine site in Japan on AMD that contains iron and zinc ions. The passive treatment system consisted of two reactors. AMD was first introduced into an iron oxidation reactor filled with rice husk to promote iron oxidation and capture iron oxides. The reactor had a flow rate of ~5.2 L/min and an HRT of 2.5 hours. AMD was introduced as a shower to increase dissolved oxygen. Total iron in this reactor was decreased from 30-40 mg/L to < 10 mg/L. The anaerobic reactor contained three layers to reduce sulfate ions and metal ions as sulfides: a bottom limestone layer, middle rice husk/limestone/soil layer for SRB reaction, and a top rice bran layer. The anaerobic reactor had a flow rate of ~2.6 L/min and an HRT of 30 hours. The rice husk layer was later thickened to promote more effective zinc removal. After the layer was thickened, zinc concentration measured ~0 mg/L in nonfiltered effluent samples. See pages 195-198:

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