The gas-to-liquid (GTL) process generates considerable amounts of wastewater that are highly acidic and characterized by its high chemical oxygen demand (COD) content, due to the presence of several organic pollutants, such as alcohols, ketones, aldehydes, and fatty acids. The presence of these organics in the process water may lead to adverse effect on the environment and aquatic life. Thus, it is necessary to reduce the COD content of GTL process water to an acceptable limit before discharging or reusing the treated water. Due to several advantages, biological treatment is often utilized as the main step in GTL process water treatment plants. In order to have a successful biotreatment process, it is required to choose effective and suitable bacterial strains that have the ability to degrade the organic pollutants in GTL process water. In this work, bacterial strains were isolated from the GTL process water, identified by 16S rRNA gene sequencing and then used in the biodegradation process. The detailed identification of the strains confirmed the presence of three organics-degrading bacteria identified as Alcaligenes faecalis, Stenotrophomonas sp., and Ochrobactrum sp. Furthermore, biodegradation experiments were carried out and confirmed that the pure culture as well as the mixed culture consortium of the bacterial strains has the ability to reduce the organic pollutants in GTL process water. However, the growth rate and biodegradation efficiency depend on the type of strains and the initial COD content. Indeed, the removal percentage and growth rate were enhanced after 7 days for all cultures and resulted in COD reduction up to 60%. Moreover, the mixed culture of bacterial strains can tolerate and treat GTL process water with a variety of ranges of COD contents.

Gas-to-liquid (GTL) technology involves the conversion of natural gas into several liquid hydrocarbon products. The Fischer-Tropsch (F-T) process is the most widely applied approach for GTL, and it is the main source of wastewater in the GTL process. The wastewater is generally characterized by high chemical oxygen demand (COD) and total organic carbon (TOC) content due to the presence of alcohol, ketones and organic acids. The discharge of this highly contaminated wastewater without prior treatment can cause adverse effects on human life and aquatic systems. This review examines aerobic and anaerobic biological treatment methods that have been shown to reduce the concentration of COD and organic compounds in wastewater. Advanced biological treatment methods, such as cell immobilization and application of nanotechnology are also evaluated. The removal of alcohol and volatile fatty acids (VFA) from GTL wastewater can be achieved successfully under anaerobic conditions. However, the combination of anaerobic systems with aerobic biodegradation processes or chemical treatment processes can be a viable technology for the treatment of highly contaminated GTL wastewater with high COD concentration. The ultimate goal is to have treated wastewater that has good enough quality to be reused in the GTL process, which could lead to cost reduction and environmental benefits.

This study investigates the characterization and the ability of polyvinyl alcohol (PVA) gel to be used in the area of wastewater treatment as biomass immobilization matrix. The PVA matrix was prepared through the freezing-thawing cross-linking process under several preparation conditions including freezing-thawing temperature and number of cycles. PVA morphology and pore structure were tested using SEM analysis. In addition, mechanical characterization of the PVA gel was carried out using compression tests. The optimum conditions for the preparation of PVA gel with high pore structure and mechanical strength were determined to be freezing at-20C and thawing at +20C, and this can be achieved at 4 or 8 iterative freezing-thawing cycles. The prepared PVA gel under these conditions can be utilized for biomass immobilization in the area of biological wastewater treatment.