A Novel Submerged Photocatalytic Oscillatory Membrane Reactor for Effluent Water Polishing
Abstract
With water scarcity being identified as a serious challenge around the world, wastewater recycling is paramount for effective water management. To achieve effective water reuse while maintaining low treatment cost, process-intensification (PI) of tertiary treatment technologies is imperative.
In this research, multilayer process-intensification approaches are investigated for effluent water polishing. Initially, the performance of a hybrid submerged photocatalytic membrane reactor (SPMR) was investigated. In a SPMR, both pollutant degradation and catalyst separation (from the permeate) occur in a single modular unit.
The design was enhanced by imparting periodic shear at the membrane surface via membrane oscillation acting as a second intensification layer. The performance of the developed submerged photocatalytic oscillatory membrane reactor (SPOMR) was evaluated using antipyrine as a model micropollutant (MP). Central Composite Design (CCD) and response surface analysis were used to analyze the effect of oscillation intensity and aeration rate on antipyrine removal and membrane flux. The optimum operating parameters were determined using composite desirability function and were then used to quantify the removal of three other micropollutants. Micropollutant degradation in presence of humic acid (HA) and secondary wastewater (SW) as background matrices was also characterized. Up to 90% MP removal was achieved in Milli-Q water and the performance of the reactor was significantly affected in presence of HA and SW.
To further improve the system performance, a third intensification layer was implemented using immobilized activated carbon (AC) as an additional adsorption layer in a “hybrid adsorptive-photocatalytic oscillatory membrane reactor" design. The system performance was assessed using diclofenac (DCF) as a model pollutant and the electrical energy per unit order (EEO) was determined. Membrane Oscillation helped in alleviating fouling and increasing the photocatalytic efficiency of the system and using AC as an additional adsorption layer nearly doubled the DCF removal rate. However, the performance of the system declined overtime mainly due to exhaustion of AC and decrease in TiO2 photocatalytic efficiency.
In addition, a mathematical model was developed to understand the forces acting on the catalyst particles near the membrane vicinity at various aeration rates and membrane oscillations. The model helped in predicting the operating conditions for fouling alleviation at various permeate flow rates.
In conclusion, significant process intensification can be achieved using the proposed approaches and could offer a promising potential as a final water polishing step.