Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Chemical and Biochemical Engineering

Collaborative Specialization

Environment and Sustainability

Supervisor

Ray, Madhumita B.

2nd Supervisor

Gomaa, Hassan

Co-Supervisor

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.

Summary for Lay Audience

With an increase in global population and economies growing around the world, production of chemicals is expected to increase proportionately. At present, more than 100,000 chemicals are registered in Europe and most of them get transported into water bodies thereby polluting water resources.

Emerging contaminants namely pharmaceuticals, personal care products (PPCPs) etc. are constantly detected in trace concentrations and their presence in water has been associated to a numerous harmful effects on both humans and aquatic life. In order to recycle water for various purposes, removal of these compounds is of utmost importance and an effective technology for treatment of these emerging contaminants is proposed.

This thesis reports the performance of a novel photocatalytic oscillatory membrane reactor for effluent water polishing. The reactor is a hybrid system employing photocatalysis and an oscillatory membrane in a single modular unit. While photocatalysis is capable of degrading pollutants and mineralizing them to CO2, the membrane helps in keeping the catalyst in the system with oscillations alleviating membrane fouling. These three processes work in tandem and synergizes the overall process. In later stages of this thesis, an additional (immobilized) layer of adsorbent was added to the system, further enhancing the efficiency of the process. The results obtained indicate that up to 90 % removal of pollutant was achieved and the performance of the system declined in presence of background organics in water. The operational cost of the system was estimated to be 2.2-4.4 $/m3.

The technology investigated in this research is effective in removing trace contaminants from water and hence can be used from water recycling purposes.

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