Co-conversion of gaseous carbon dioxide and a high strength aqueous organic contaminant (phenol) to methane via a UASB reactor

More economical and efficient means are required to decrease or to recover greenhouse gases (GHG) exhausted into the environment, and to decrease the amount of wastewater that is degrading the water bodies worldwide. Therefore the objective of this research is to develop a system that will treat both carbon dioxide and a high strength wastewater; for this purpose an Up-flow Anaerobic Sludge Blanket (UASB) reactor was used. Previous studies showed that carbon dioxide could be converted to methane with organic acids. In this study, the addition of carbon dioxide will act as the co-substrate needed in order to treat higher concentrations of the toxic pollutant phenol in wastewater without any recirculation of the effluent. This is based on previous studies that showed that higher concentrations (1260 mg/L phenol) can be treated if a co-substrate is added. An anaerobic biomass used for this experiment was taken from two reactors treating sucrose and acetic acid. Then, it was acclimated by increasing stepwise the concentration of phenol, while reducing the concentration of sucrose and/or acetic acid. Methanogenic activity tests were performed to evaluate the toxicity limits of phenol toward the biomass. Two sets of two reactors were used. The first set contained the biomass acclimated with sucrose; the second set contained the biomass acclimated with acetic acid. Control reactors had phenol added as the carbon source; whereas in the other reactors, carbon dioxide was added as the co-substrate. The parameters monitored were chemical oxygen demand, volatile suspended solids, methane content of the biogas and production, phenol concentrations, alkalinity, and dissolved carbon dioxide. It was shown that both CO 2 and phenol could be degraded in an UASB reactor with reduction values that ranged from 86-88% and 86-94% respectively. Total COD reduction ranged from 92-97% and methane content in the biogas ranged from 64-70%. The biomass showed a steady organic content throughout the experiment after a sudden decrease during the acclimation period. Overall, the reactors with the best performances were R4 (acetic acid-fed biomass with CO 2 ) and R2 (sucrose-fed biomass with CO 2 ) although this last one showed some performance similarities with R3 (acetic acid-fed biomass without CO 2 ) and the reactor which was more prone to loading shock was R1. Carbon dioxide, a waste gas, poses a great advantage in the anaerobic process since it was proven to be a good co-substrate in the biodegradation of a high strength wastewater, with a higher methane recovery. Adding carbon dioxide to UASB reactors in order to boost degradation instead of releasing it to the environment is a good remediation proposal