Development and Evaluation of Nanoparticles-based Biocatalysts for the Treatment of Gas-to-Liquid (GTL) Process Water

One of the main sources of wastewater in Qatar's Gas-To-Liquid (GTL) process water is the reaction water from the Fischer-Tropsch (F-T) unit. This water is characterized by its high acidity and high COD content. The application of immobilized bacteria in polymeric matrix, such as polyvinyl alcohol (PVA) gel has gained attention due to its effectiveness in addressing diverse environmental challenges. The immobilization system employs various biomasses for the biodegradation of organic water pollutants, such as hydrocarbons commonly found in process water and industrial wastewater.

This study explores the amalgamation of nano-biotechnology in the bio-treatment of contaminated water, with a specific emphasis on GTL process water. It involves the development of a Spouted Bed Bioreactor (SBBR) utilizing indigenous biomasses adaptable to Qatar's environment and applied within an immobilized system. These bioreactors can advance bioprocesses to manage various environmental challenges in the Qatari gas industry, including contaminated water treatment and recycling. This study's overarching goal is to create efficient biocatalysts using locally available bacteria adapted to the environment and employ these biocatalysts for GTL process water treatment. It involves several stages, including the isolation and characterization of organic-degrading bacteria, testing of nanoparticles as reinforcement for Polyvinyl Alcohol (PVA) gel matrices, and the design and utilization of a Spouted Bed Bioreactor (SBBR) system for continuous biological treatment. It also investigates the influence of external and internal mass transfer on the biodegradation of organic pollutants in GTL process water, assessing the impact of mixing intensity using immobilized bacteria in PVA/TiO2 bio-carriers. Key findings encompass variations in external mass transfer coefficients, boundary layer thickness, and the examination of maximum oxygen and Chemical Oxygen Demand (COD) fluxes.

The research findings encompassed the isolation of three organic-degrading bacterial strains from GTL process water, offering promising alternatives to conventional activated sludge systems for efficient organic pollutant removal. These versatile strains demonstrated the ability to work independently or in mixed cultures, achieving a remarkable 60% COD reduction even in the complex GTL process water composition. Additionally, PVA nanocomposites with TiO2 nanoparticles were introduced as effective matrices for biomass immobilization, maintaining biodegradation performance. The study optimized batch biological treatment using Response Surface Methodology, providing a predictive model for improved treatment. The continuous biological treatment system for GTL process water showed distinct responses to organic and hydraulic shock loads, with hydraulic shocks having a more significant impact; however, the system demonstrated robust stability and quick recovery in both scenarios. System stability was negatively affected by fluctuations in air flow rate, resulting in reduced dissolved oxygen levels and decreased organic removal efficiency. Despite these challenges, the continuous biological treatment approach proved effective in achieving significant COD reduction and system stabilization, with optimal outcomes observed under specific operational conditions. Continuous biological treatment effectively reduced COD by 78% under varying conditions, showing the system's resilience. Lastly, external mass transfer primarily influenced biodegradation, with implications for scaling up similar treatment systems in various wastewater processes.