Cold Water Starch Dissolution Bioreactors: Role in Treating Heap Leached Wastewater from Precious Metal and REE Ores
Sodium cyanide, like other soluble cyanide salts, is among the most rapidly acting of all known poisons. Acting on mitochondrial cytochrome oxidase and hence blocking electron transport, NaCN is a potent inhibitor of respiration. This causes decreased oxidative metabolism and oxygen utilization followed by Lactic acidosis resulting from anaerobic metabolism. An oral dosage as small as 200 300 mg can be fatal. At abandoned mines, it is postulated that the alkaline cyanide wastewater from heap leaching of precious metals can be microbially degraded if alkaliphilic bacteria and a suitable microbial substrate can provided. The facultative alkaliphile pseudoalcaligenes CECT5344 was identified as being capable of degrading cyanide and metal complexed cyanides in wastewater with a pH of up to 11. The aim was to provide a self generating continuous source of a suitable, low cost microbial substrate in anaerobic conditions. "Bitter" Bambusa vulgaris (bamboo) chips from freshly harvested 1 and 2 year old plants were submerged in neutral (pH 7) cold water for 15 days. This process dissolved starch which was then leached from the bamboo. The system acted as a cold water anaerobic bioreactor because (1) anaerobes produced alcohol using the leached bamboo sugars, (2) starch dissolution and release was perpetuated. The starch dissolution was attributed to reactions between alkalis from the intrinsic alakloids in the cells of "bitter" bamboo, and the alcohols produced by yeast fermentation. This slow release, continuous source of starch is a potential substrate for degradative anaerobes exposed to the cyanide in wastewater from heap leaching. Moreover, this nutrient source can be applied to heavy metal detoxification of acidic wastewater such as those from REE heap leaching, after neutralization by SRB's.