A mixed microbial community for the treatment of free cyanide and Thiocyanate containing wastewater

Abstract

Industrial wastewater management pertaining to the mining industry has become increasingly stringent, with companies being required to develop environmentally benign wastewater management practices worldwide. The industries that utilise cyanide compounds for the recovery of precious and base metals in a process known as the cyanidation process, have contributed substantially to environmental deterioration and potable water reserve contamination due to the discharge of poorly treated, or untreated, cyanide containing wastewater. Hence, a biotechnological approach was undertaken in this study to remediate free cyanide (CN-) and thiocyanate (SCN-), which are the major chemical contaminants which are normally found in cyanidation wastewaters. Furthermore, this biotechnological approach was investigated to understand the fundamental aspects of using this approach such that the information gathered can be utilized in pilot plant studies. Therefore, bioprospecting of potential CN- and SCN--degrading organisms was undertaken using two approaches; (i) culture-dependent approach and (ii) culture-independent approach. Using the culture-dependent approach, Pseudomonas aeruginosa STK 03, Exiguobacterium acetylicum and Bacillus marisflavi were isolated from an oil spill site and river sediment samples, respectively. STK 03 was evaluated for the biodegradation of CN- and SCN- under alkaline conditions. The organism had a CN- degradation efficiency of 80% and 32% from an initial concentration of 250 and 450 mg CN-/L, respectively. Additionally, the organism was able to degrade SCN-, achieving a degradation efficiency of 78% and 98% from non- and CN- spiked cultures, respectively. Furthermore, the organism was capable of heterotrophic nitrification but was unable to denitrify aerobically, with the autotrophic degradation of CN- by STK 03 being abortive.