A lab scale pellet reactor (PR) was designed and fabricated to carry out extensive investigations on the removal efficiency of the hardness of groundwater.  The groundwater of 2200 – 2600 mg/L hardness was collected from Abdulla Ibnalhassan wells area located at the west desert of Al-Shinafiyah district (70 km to the southwest of Al-Dewaniyah city, Iraq). Both hydrodynamic parameters of the pellet reactor (porosity and fluidized bed height) and the parameters of calcium carbonate crystallization process (calcium carbonate equilibrium, pellet size, and density) were modeled and compared with the experimental results of the lab scale pellet reactor. The comparison showed that fair agreement between modeled and measured results was observed. The removal efficiency of both calcium and magnesium ions were 62.5-99% and 83-99% respectively. The removal efficiency was found to be strongly dependent on pH and the ratio of NaOH solution flow rate to the groundwater flow rate in the pellet reactor.

Overall gas-liquid mass transfer coefficients of oxygen gas (KLa) at different axiallocations of the riser and downcomer of a split-column Airlift Photobioreactor wereinvestigated using FOXY Fiber Optic oxygen sensor supported by NeoFox viewer software.The effect of bubble dynamics on mass transfer was considered. A 4-point optical probe wasused to measure local interfacial area (a) and other bubble dynamics parameters for both theriser and the downcomer of a split-column airlift photobioreactor. Having both overall masstransfer (KLa) and interfacial area (a) measured at different locations, local oxygen masstransfer coefficient (KL) can be determined for each location along the riser and thedowncomer of the airlift bioreactor. Effects of different operating conditions (0.3 – 2.8 cm/ssuperficial gas velocity) on both mass transfer and bubble dynamics of the riser and thedowncomer have been investigated for air-water system. It was found that both local masstransfer and gas-liquid interfacial area are considerably varying from the bottom to the top ofthe riser and the downcomer of the bioreactor. It was found that local mass transfer coefficientvaries by 100% from the bottom to the top of the riser at low superficial gas velocity (1 cm/s)and by 30% at relatively high velocities (2-2.8 cm/s). The Trend of the variation of the KLa inthe downcomer section of the column is very different from that of the riser, as it was noticedthat insignificant mass transfer takes place at the lower part of the downcomer. The results ofmass transfer and bubble dynamics in the riser and the downcomer of the studied conditionswill be presented and discussed.