| Summary: | This study provides a performance comparison of arsenic, cadmium and zinc treatment at mildly
acid to neutral pH in an anaerobic bioreactor (ABR) column experiment operated at 4°C and
25°C. The materials and contaminants were based on a field scale system operated by Nature
Works Remediation Corp. for Teck Cominco Metals Ltd. in Trail, BC. The majority of arsenic
was removed within the oxic zones of the ABR columns. Although it was thought that arsenic
removal at this stage was attributed to sorption to iron, it is now known to be zinc arsenate. The
work showed cadmium and zinc removal improved in relation to the extent of anoxic conditions
in the columns. In the most anaerobic zone of the columns (i.e., characterized by good sulphate
reducing bacteria (SRB) activity) effective zinc removal required a stable SRB population, but
was not necessarily temperature dependent. However, there was a direct and significant impact to
microbial activity as a result of a temperature change. The work suggested that internal
monitoring of DO and SRB can provide valuable information with respect to significant metal
removal mechanisms, and the active volume in which metal sulphides can be significantly
generated. The information can be used to: troubleshoot an under-performing system, and make
appropriate amendments to improve system performance.
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