Fate of organic fractions of greywater in combined process of vacuum-ultraviolet (VUV/UV)/ozone pre-oxidation with enhanced coagulation

Pre-ozonation is often used as an effective method to assist coagulation in removing organic contaminants. In this study, a new process that combining ozone (O-3) with vacuum ultraviolet (VUV/UV) process (VUV/UV/O-3) is investigated to enhance the removal of organic matters in greywater from public buildings or household. The influence of organic characteristics (molecular weight distribution, hydrophobicity, and fluorescence) in grey water on VUV/UV/O-3 enhanced coagulation has not been fully studied. Herein, organic matters of greywater were separated and classified, and fates of organic fractions by VUV/UV/O-3 enhanced coagulation were clarified. Greywater contains tryptophan-like and tyrosine-like proteins, and terrestrially derived humic-like substances. The highest UV254, LAS, DOC and CODCr removal efficiency from greywater could reach up to 47.54%, 58.92%, 17.96% and 15.76% in VUV/UV/O-3 enhanced coagulation, respectively. The removal efficiency of tryptophanlike and tyrosine-like in filtrates of varied molecular weight ranges by VUV/UV/O-3 enhanced coagulation was 93.59%-98.13% and 89.86%-95.53%, respectively. VUV/UV/O-3 enhanced coagulation was effective for the removal of bio-polymers, humic substances and low molecular weight acid <=& nbsp;30 kDa, while it was insignificant for that of 0.22 mu m 100 kDa. Particle size of flocs increased significantly in filtrates obtained from increasing membrane pore size, indicating that macromolecular organic matter was more likely to form flocs. Finally, the VUV/UV/O-3 could improve coagulation on the removal of varied organic pollutants and improve sedimentation by changing the flaky flocs to dense ones. Therefore, the results demonstrate VUV/UV/O-3 is an effective pre oxidation method to enhance the effect of coagulation on greywater treatment.