Heavy Metal Removal via Phycoremediation

Acid Rock Drainage (ARD) is a growing environmental problem and is characterized by acidic, heavy metal-laden water. Here we consider the use of algae to remediate ARD and heavy metal pollution. Algae species candidates that remediate heavy metals from impacted waters with a 90% efficiency while sustaining highly acidic, metal-laden conditions were explored. The following phycoremediation candidates were selected, cultivated, and intended to be tested for their metal-sorption capacity and ideal operational conditions: Spirulina platensis, Cladophora glomerata, a sample from mine water, and a sample local to New Orleans, Louisiana. Due to the unexpected remote-only working constraints, only the local sample was tested for its metal removal efficiency on synthetic multi-metal mine water and at only one operational condition: contact time. Optimum contact times varied upon the different metals: 75 minutes (Al), 15 minutes (As), 60 minutes (Cu), and 30 minutes (Fe, Mn, and Zn).After practicing phycoremediation in the lab, a full-scale system for mass-cultivation of algae and treatment of acid rock drainage with an influent flow rate of 10 GPM was designed. An ORWP was selected for the mass-cultivation of the algae and the required pond area was determined to be 700 m
²
. For the treatment system, a sequencing batch reactor (SBR) design was selected with three batch reactors each with a volume of 1500 gallons to account for a 10 GPM flow per tank per cycle. To separate the biomass from the treated mine water, a concurrent inclined settling system and flocculant was chosen. A mass balance was applied to the system to find the flow of biomass exiting and the amount of truckloads per year required for disposal of the biomass. From a cost analysis, the estimated capital and annual costs of a full-scale ARD treatment phycoremediation system is estimated to be $361,943 and $244,821/year, respectively.