Characteristics of developed granules containing phototrophic aerobic bacteria for minimizing carbon dioxide

Abstract

Aerobic wastewater treatment has contributed to the greenhouse gases (GHG) emission in the atmosphere, which can cause global warming. The GHG consists of six major gases particularly carbon dioxide (CO2). Existing biological system of the wastewater treatment needs to be reviewed in order to minimize the emission of GHG especially CO2. Some findings had shown that photosynthetic bacteria can be employed for CO2 utilization during the wastewater treatment processes. The aim of this study was to characterize phototrophic microbial granule in order to minimize CO2. Synthetic wastewater was used throughout this study to obtain the aerobic granules. A 3-L bioreactor phototrophic Sequencing Batch Reactor (SBRP) was applied to produce phototrophic aerobic granular sludge (AGSP) and the biomass concentration increased from 3 to 14gL-1. Such growth has resulted in a maximum settling velocity of 40mh-1 with granule average size of ~ 2.0mm. The high settling velocity was found to be attributed by the smooth, compact, and regular characteristics of the aerobic granules. High magnification microscopic analysis revealed that AGSP was dominated by cocci-shaped bacteria embedded within the extracellular polymeric substances (EPS). Detailed observation on the structure of the AGSP showed the presence of 30µm of cavity to allow nutrients and gas exchanges within the aerobic granule. Scanning Electron Microscope-Energy-Dispersive X-ray (SEM-EDX) examination showed AGSP composed of different types of inorganic and organic compounds. AGSP achieved 92% of CO2 reduction and 84% of chemical oxygen demand (COD) removal.