A novel approach to exploit indigenous mining algal-microbes in a photo-rotating biological contactor for heavy metal removal from acid mine drainage

Abstract

Extremophilic acidic microbial biofilms, that thrive in acidic mine drainages (AMD), are well known as natural metal-resistant biosorbents for removing heavy metals throught active and passive cellular functions. To benefit from the resistant and cleansing nature of these microorganisms and to develop a system applicable to mining sites, an indigenous AMD biofilm was immobilized in a laboratory scale photo-rotating biological contactor (PRBC) to investigate its heavy metal removal potential from AMD. The microbial consortium used for biofilm development contained filamentous green micro-algae, bacteria, fungi and yeasts, collected from AMD and the Sarcheshmeh copper mine in Iran. The PRBC was operated with synthesised AMD representing the multi-ion and acidic composition of the wastewater (composing 18 elements with a pH of 3.5+0.3) from which the microbial consortium was collected. Light, nutrient dosing and rotational speeds were optimised to encourage biofilm development. Electron microscopy was used to monitor the development of the algal-microbial biofilm on the PROBC discs over a 60 day batch mode operation. The PRBC was then run continuously with a 24 h hydraulic residence time (HRT) over a ten week period. The weekly average of water analysis results demonstrated the ability for the algal-microbial biofilm to remove 15-50% of various metals in the order of Cu> Ni> Mn> Zn> Sb> Cr> Co> Al. These results clearly indicate the significant potential for indigenous AMD biofilm to be exploited within a PRBC for AMD treatment.