| Abstract: | Aims to investigate the performance of the pilot-scale reclamation plant for coal gasification wastewater (CGW) using ultrafiltration and reverse osmosis with appropriate pretreatment alternatives, different pre-treatment alternatives- coagulation, adsorption, and ozonation methods were employed to treat the secondary effluent of coal gasification wastewater (SECGW) in a pilot-scale pressurized membrane system. The performance was compared to choose the most suitable pre-treatment alternative for the SECGW reclamation. Ozone reaction achieved highest COD removal efficiency (79.6%-91.0%), resulting in the stable normalized parameters of the subsequent ultrafiltration and reverse osmoses. In contrast, the coagulation and adsorption processes achieved only 32.8%-45.7% and 53.1%-64.6% decreases in COD, respectively. The residual organic pollutants in the reverse osmosis feed water led to an increase in normalized pressure drop and a decrease in normalized permeability (or membrane transference coefficient). The hydrophobic fraction was the main constituent (approx. 70% of DOC) in pretreated SECGW, and the hydrophobic-neutral fraction contributed mostly to the UV absorbance (53%). Fluorescence excitation emission matrices revealed that ozonation removed most of the hydrophobic and aromatic proteins such as tyrosine and tryptophan which dominated in raw wastewater. The recalcitrant compounds such as phenolic compounds, heterocyclic compounds, especially long-chain hydrocarbons, which were easily attached to the membrane surface and contributed to organic fouling, could be oxidized and mineralized by ozone. Among the three pretreatments, ozonation showed highest removal efficiencies of hydrophobic and aromatic proteins, therefore resulting in highest normalized permeability. |
