Submerged bed versus unsaturated flow reactor: A pressurized hydrogenotrophic denitrification reactor as a case study

The paper compares the main features of a submerged bed reactor (SuBR) with bubbling and recirculation of gas to those of an unsaturated flow reactor (uSFR) with liquid recirculation. A novel pressurized closed-headspace hydrogenotrophic denitrification system characterized by safe and economic utilization of H2 gas was used for the comparison. Under similar conditions, denitrification rates were lower in the SuBR as a result of a lower effective biofilm surface area and overall gas-liquid mass transfer coefficient kLa. Similar values of effluent DOC were achieved for both reactors, although effluent suspended solids concentration of the SuBR were substantially higher. On the other hand, the required cleaning frequency in the SuBR was 2.5 times lower. Moreover, the SuBR is expected to reduce the recirculation energy consumption by 0.35 kWh/m3 treated. •Two modes of pressurized hydrogenotrophic denitrification reactor were compared.•The unsaturated-flow mode with liquid recirculation presented higher rates and kLα.•The unsaturated-flow mode with liquid recirculation presented lower effluent TSS.•The operation under saturated-flow mode with gas recirculation was more stable.•Energy consumption of gas recirculation is expected to be significantly lower.