Use of an algal consortium of five algae in the treatment of landfill leachate using the high-rate algal pond system

Abstract

Five species of microalgae Chlorella vulgaris, Scenedesmus quadricauda, Euglena gracilis, Ankistrodesmus convolutus and Chlorococcum oviforme, were screened for their ability to grow in treated landfill leachate (TL) using shake flask cultures. The treated leachate had undergone previous treatment through mechanical aeration in treatment ponds at the landfill site. The five algae, except for C. oviforme, were able to grow in medium containing up to 50% TL. Two high-rate algal ponds (HRAP) equipped with paddlewheel were used for the semi-continuous cultures. A mixture of the five algae was used to inoculate one of two HRAPs for secondary treatment of TL. The other HRAP was filled with natural lake water containing mixed populations of algae. A volume of 400 mL (1%) from both ponds were removed daily and replaced with TL. The leachate loading rate was increased to 2% (0.8 L day⁻¹) on day 197 and then to 4% (1.6 L day⁻¹) on day 309, providing hydraulic retention time of 100, 50 and 25 days, respectively. Although higher biomass was obtained in the HRAP containing the consortium of five algae, there was no significant difference in reduction of pollutants between the two ponds. The HRAPs produced algal biomass ranging from 2.00 to 5.54 g dry weight L⁻¹ with significant reduction in chemical oxygen demand (91.0%), ammoniacal nitrogen (99.9%) and orthophosphate (86.0%) contents. The HRAP offers a potential treatment system for TL which is simple, low cost, flexible in use and requiring low maintenance.